Class 10 Biological Science Textbook NCERT

Biology
Smt. Kasula Rama Mani MSc, MEd.
Prof. in Biology, SCERT, AP
Dr. Ch.V.S. Ramesh Kumar
Faculty, SCERT-AP

Asst. Subject Co-Ordinator
Dr. Y. Giri Babu Yadav,
Professor, SCERT, AP
Smt. S. Bhanumathi
Lecturer, SCERT, AP
Smt. V. Sarada Devi
Lecturer, SCERT, AP
Sri Sk. Mohammad Gouse
Assessment Cell, SCERT, AP
Dr. T.V.S. Ramesh
School Assistant (BS), ZPHS, Nagula Vellaturu, Chejerla (M)
SPSR Nellore Dist.
Smt. S. Uma Maheswari
School Assistant (BS), ZPHS, IPPILI, Srikakulam (M), Srikakulam Dist.
Sri P. Satya Prakash
School Assistant (BS), ZPHS, Konda Gumpam, Nellimarla (M),
Vizianagaram Dist.
Sri. Y. Hemasundara Rao
H.M, Govt. High School,
Seethampeta, Seethampeta (M)
Parvathipuram Manyam Dist.
Sri Nusum Chinna Moula
School Assistant (BS), MVRR ZPPHS,
Narasapuram, Indukurpet (M) SPSR Nellore Dist.
Smt. S. Uma Maheswari
School Assistant (BS), ZPHS, IPPILI,
Srikakulam (M), Srikakulam Dist.
Sri P. Satya Prakash
School Assistant (BS), ZPHS,
Konda Gumpam, Nellimarla (M),
Vizianagaram Dist.
Sri. N. Kumaraswamy
H.M, ZPHS, Rompivalasa,
Pathapatnam (M), Srikakulam Dist.
Smt. K. Manjula
School Assistant, (BS) ZPHS
Palasamudram, Gorantla (M)
Sri Satya Sai Dist.

CHAIRMAN, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS
J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee Inter University Centre for
Astronomy & Astrophysics (IUCCA), Ganeshbhind,
Pune University, Pune
CHIEF ADVISOR
Rupamanjari Ghosh, Professor, School of Physical Sciences, Jawaharlal Nehru University, New Delhi
MEMBERS
Anjni Koul, Lecturer, Department of Education in Science and Mathematics (DESM), NCERT, New
Delhi
Anupam Pachauri, 1317, Sector 37, Faridabad, Haryana
Anuradha Gulati, TGT, CRPF Public School, Rohini, Delhi
Asfa M. Yasin, Reader, Pandit Sunderlal Sharma Central Institute of Vocational Education, NCERT,
Bhopal
Charu Maini, PGT, DAV School, Sector 14, Gurgaon, Haryana
Dinesh Kumar, Reader, DESM, NCERT, New Delhi
Gagan Gupta, Reader, DESM, NCERT, New Delhi
H.L. Satheesh, TGT , DM School, Regional Institute of Education, Mysore
Madhuri Mahapatra, Reader, Regional Institute of Education, Bhubaneswar, Orissa
Puran Chand, Joint Director, Central Institute of Educational Technology, NCERT, New Delhi
S.C. Jain, Professor, DESM, NCERT, New Delhi
Sujatha G.D., Assistant Mistress, V.V.S. Sardar Patel High School, Rajaji Nagar, Bangalore
S.K. Dash, Reader, DESM, NCERT, New Delhi
Seshu Lavania, Reader, Department of Botany, University of Lucknow, Lucknow
Satyajit Rath, Scientist, National Institute of Immunology, JNU Campus, New Delhi
Sukhvir Singh, Reader, DESM, Regional Institute of Education, Ajmer, Rajasthan
Uma Sudhir, Eklavya, Indore
MEMBER-COORDINATOR
Brahm Parkash, Professor, DESM, NCERT, New Delhi

Director
National Council of Educational
Research and Training
New Delhi
20 November 2006
The National Curriculum Framework (NCF) 2005, recommends that children’s life at
school must be linked to their life outside the school. This principle marks a departure from the
legacy of bookish learning which continues to shape our system and causes a gap between
the school, home and community. The syllabi and textbooks developed on the basis of NCF
signify an attempt to implement this basic idea. They also attempt to discourage rote
learning and the maintenance of sharp boundaries between different subject areas. We
hope these measures will take us significantly further in the direction of a child-centred system
of education outlined in the National Policy on Education (1986).
The success of this effort depends on the steps that school principals and teachers will
take to encourage children to reflect on their own learning and to pursue imaginative
activities and questions. We must recognise that, given space, time and freedom, children
generate new knowledge by engaging with the information passed on to them by adults.
Treating the prescribed textbook as the sole basis of examination is one of the key reasons why
other resources and sites of learning are ignored. Inculcating creativity and initiative is
possible if we perceive and treat children as participants in learning, not as receivers of a fixed
body of knowledge.
These aims imply considerable change in school routines and mode of functioning.
Flexibility in the daily time-table is as necessary as rigour in implementing the annual calendar
so that the required number of teaching days are actually devoted to teaching. The methods
used for teaching and evaluation will also determine how effective this textbook proves for
making children’s life at school a happy experience, rather than a source of stress or
boredom. Syllabus designers have tried to address the problem of curricular burden by
restructuring and reorienting knowledge at different stages with greater consideration for
child psychology and the time available for teaching. The textbook attempts to enhance this
endeavour by giving higher priority and space to opportunities for contemplation and
wondering, discussion in small groups, and activities requiring hands-on experience.
The National Council of Educational Research and Training (NCERT) appreciates the
hard work done by the textbook development team responsible for this book. We wish to
thank the Chairman of the advisory group in science and mathematics, Professor J.V. Narlikar
and the Chief Advisor for this book, Professor Rupamanjari Ghosh, School of Physical
Sciences, Jawaharlal Nehru University, New Delhi, for guiding the work of this committee.
Several teachers contributed to the development of this textbook; we are grateful to them
and their principals for making this possible. We are indebted to the institutions and
organisations which have generously permitted us to draw upon their resources, material and
personnel. We are especially grateful to the members of the National Monitoring Committee,
appointed by the Department of Secondary and Higher Education, Ministry of Human
Resource Development under the Chairmanship of Professor Mrinal Miri and Professor G.P.
Deshpande, for their valuable time and contribution. As an organisation committed to
systemic reform and continuous improvement in the quality of its products, NCERT welcomes
comments and suggestions which will enable us to undertake further revision and refinement.

Dr. B. Pratap Reddy
Director, SCERT
Andhra Pradesh

The Government of Andhra Pradesh has unleashed a new era in school education by
introducing extensive curricular reforms from the academic year 2020-21. The Government
has taken up curricular reforms intending to enhance the learning outcomes of the children
with focus on building solid foundational learning and to build up an environment
conducive for an effective teaching-learning process. To achieve this objective,
Government of Andhra Pradesh has decided to implement the NCERT curriculum for Class
10th from the academic year 2024-25 to reach the global standards.
As a part of the curriculum reform, SCERT, Andhra Pradesh has translated the NCERT
content of Biological Science into Telugu language with the consent of NCERT and
developed it into Bilingual textbook. QR codes are incorporated in the beginning of each
lesson to enrich the content of the subject and to enable learning outside the classroom. In
this textbook, lessons on the themes like Living world and Natural Resources are incorporated
under Biological Science. In order to reinforce the concepts, several projects and activities
are given to inculcate scientific temperament. Each lesson is provided with eye catching
illustrations to engage the children. The salient features of the lessons are given under the title
“What you have learnt” for the review of the important concepts. Questions are framed for
each lesson to recapitulate the conceptual understanding. To achieve competencies
required drawings, activities, project works, model making are given in the content. Do you
know, More to know, Think it over are given in the text book to give additional information. An
effort has been made to relate the scientific concepts with the real-life events thereby
developing and promoting scientific temperament. “Exercises” have been given for
assessment which helps students to scale-up further in their learning of concepts.
We are grateful to our Honourable Chief Minister Sri Y.S. Jagan Mohan Reddy for being
our source of inspiration to carry out this extensive reform in the Education Department. We
extend our gratitude to our Honourable Minister of Education Sri Botcha Satyanarayana for
striving towards qualitative education. Our special thanks to Sri Praveen Prakash, IAS, Principal
Secretary to Govt., School Education, Sri S. Suresh Kumar, IAS, Commissioner of School
Education, Sri B. Srinivasa Rao, IAS, State Project Director, Samagra Shiksha A.P, for their
constant motivation and guidance.
We convey our special thanks to the NCERT for their cooperation and assistance in
adopting their curriculum. We also thank our translators, editors and layout designers for their
contribution in the development of this textbook. We invite constructive feedback from the
teachers and the parents in further refinement of the textbook.

This textbook of Science for Class X is a continuation of our attempt in the Class IX
Science textbook to comply with the guidelines of the National Curriculum Framework-
2005. We had to work within a limited time frame and also had our own constraints coming
in the way of this radical change. The revised and re-structured syllabus for Class X covers
selected topics in the broad themes of — Materials, The World of the Living, How Things
Work, Natural Phenomena and Natural Resources. We have interpreted the syllabus to
present a coherent coverage of scientific concepts related to our daily life on the select
topics. It is an integrated approach to science at this level, with no sharp divisions into
disciplines such as Physics, Chemistry, Biology and Environmental Science.
There has been a conscious attempt to address the relevant social concerns in this
science textbook wherever possible — the concerns for people with special needs, the
issues of gender discrimination, energy and environment have found their natural place in
this book. Students have been encouraged to get into the debates on some of the
management concerns (for sustainable development, for example) so that they can
arrive at their own decisions after a scientific analysis of all the facts.
This book has some features which are meant to enhance its effectiveness. The
theme of each chapter has been introduced with examples from daily life, and if possible,
by a relevant activity that the students have to perform. The entire approach of the book
is, in fact, activity-based, i.e., the students are required to construct knowledge
themselves from these activities. The emphasis is not on definitions and technical terms,
but on the concepts involved. Special care has been taken so that the rigour of science is
not lost while simplifying the language. Difficult and challenging ideas, which are not to be
covered at this stage, have often been placed as extra material in the boxes in light
orange. The excitement of doing science comes from pursuing the unknown — the
students would have the opportunity to think and explore somewhat beyond the syllabus
and may feel the urge to continue their scientific expedition at higher levels. All such box
items, including brief biography of scientists, are, of course, non-evaluative.
Solved examples are provided, wherever felt necessary, to clarify a concept. The
in-text questions after a main section are for the students to check their understanding of
the topic. At the end of each chapter, there is a quick review of the important points

covered in the chapter. We have introduced some multiple choice questions in the
exercises. There are problems of different difficulty levels answers to the multiple-choice
questions and numericals, and hints for the difficult questions are included at the end of
the book.
This book has been made possible because of the active participation of many
people. I wish to thank Professor Krishna Kumar, Director, NCERT, Prof. G. Ravindra, Joint
Director, NCERT, and Professor Hukum Singh, Head, Department of Education in Science
and Mathematics, NCERT, specially for their keen interest in the development of the book
and for all the administrative support. I wish to put on record my sincere appreciation for Dr
Anjni Koul, the member-coordinator of the textbook development committee, for her
extraordinary commitment and efficiency. It has been a real pleasure working with my
textbook development team and the review committee. The chosen editorial team
worked extremely hard, on tight deadlines, to bring the book close to the shape that we
dreamt of. Fruitful discussions with some members of the MHRD Monitoring Committee
helped in providing the final touches to the book. I do not have the words to acknowledge
the professional and personal inputs I received from some of my close friends during the
preparation of this book. We warmly welcome comments and suggestions for
improvement from our readers.
RUPAMANJARI GHOSH
Professor of Physics
School of Physical Sciences
Jawaharlal Nehru University
New Delhi

The National Council of Educational Research and Training (NCERT), besides
expressing its gratefulness towards the members of the Textbook Development
Committee for their contribution in the development of the Science Textbook for Class X,
also acknowledges the contribution of the following members for reviewing, editing,
refining, and finalisation of the manuscript of the book. Kanhiya Lal, Principal (Retd.),
Directorate of Education, NCT, Delhi; Ranveer Singh, Lecturer, Sarvodaya Bal Vidyalaya,
Timarpur, Delhi; Bharat Poorey, Professor (Retd.), Govt. Post Graduate College, Indore;
Gagandeep Bajaj, Lecturer, S.P.M. College, Delhi University, Delhi; Ravinder Kaur, TGT,
Kendriya Vidyalaya, Rohini, Delhi; Renu Puri, TGT, N.C. Jindal Public School, New Delhi;
Sarita Kumar, Reader, Acharya Narendra Dev College, Delhi University, Delhi; Shashi
Prabha, Lecturer, DESM, NCERT, Delhi; Rashmi Sharma, Lecturer, NERIE, Shillong; Sushma
Jaireth, Reader, DWS, NCERT, New Delhi; Y.P. Purang, Addl. Director of Education (Retd.),
NCT, Delhi; Neeta Agarwal, TGT, D.L.D.A.V. Model School, Pitampura, Delhi; Roma Anand,
TGT, D.L.D.A.V., Pitampura, Delhi; Veer Pal Singh, Reader, DEME, NCERT, New Delhi and
S.L. Varte, Lecturer, DESM, NCERT, New Delhi.
The Council also acknowledges the valuable contribution of Sunita Farkya
(Professor, DESM), Pushplata Verma (Assistant Professor, DESM), K.C. Tripathi (Professor, DEL)
and Jatindra Mohan Misra (Professor, DEL) in updating Chapter 16 titled "Sustainable
Management of Natural Resources", and also in the review of this textbook.
The contribution of R.S. Sindhu, Professor (Retd.), DESM; V.P. Srivastava, Professor
(Retd.), DESM; R.K. Parashar, Rachna Garg (Professors, DESM); V.V. Anand, Professor
(Retd.), RIE Mysore; S.V. Sharma (Professor, RIE Mysore); V.P. Singh (Professor, RIE Ajmer); R.
Joshi, Associate Professor (Retd.), DESM; C.V. Shimray, Ruchi Verma (Associate Professors,
DESM); Ram Babu Pareek (Associate Professor, RIE Ajmer); A.K. Srivastava, Rejaul Karim
Barbhuiya, Pramila Tanwar (Assistant Professors, DESM); R.R. Koireng (Assistant Professor,
DCS); V. Tangpu (Assistant Professor, RIE Mysore) and Akhileshwar Mishra (Head Master,
DMS, RIE Bhubaneswar), in the review of this textbook in 2017-18 are acknowledged.
Special thanks are due to Hukum Singh, Professor and Former Head, DESM, NCERT,
New Delhi, for providing all academic and administrative support.
The Council also gratefully acknowledges the support provided by the APC Office
of DESM, administrative staff of DESM; Deepak Kapoor, Incharge, Computer Station,
DESM; Saima and Arvind Sharma, DTP Operators and Rajesh Handa, Illustrator; Mohd.
Qamar Tabrez and Musarrat Parveen, Copy Editors; Seema Yadav, Proof Reader.
The efforts of the Publication Department, NCERT are also highly appreciated.

In view of the COVID-19 pandemic, it is imperative to reduce content load on students.
The National Education Policy 2020, also emphasises reducing the content load and
providing opportunities for experiential learning with creative mindset. In this background,
the NCERT has undertaken the exercise to rationalise the textbooks across all classes.
Learning Outcomes already developed by the NCERT across classes have been taken
into consideration in this exercise.
Contents of the textbooks have been rationalised in view of the following:
Ÿ Overlapping with similar content included in other subject areas in the same class
Ÿ Similar content included in the lower or higher class in the same subject
Ÿ Difficulty level
Ÿ Content, which is easily accessible to students without much interventions from
teachers and can be learned by children through self-learning or peer-learning
Ÿ Content, which is irrelevant in the present context
This present edition, is a reformatted version after carrying out the changes given above.

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H
ow do we tell the difference
between what is alive and what is
not alive? If we see a dog running, or a cow
chewing cud, or a man shouting loudly on the
street, we know that these are living beings.
What if the dog or the cow or the man were
asleep? We would still think that they were
alive, but how did we know that? We see them
breathing, and we know that they are alive.
What about plants? How do we know that they
are alive? We see them green, some of us will
say. But what about plants that have leaves of
colours other than green? They grow over time,
so we know that they are alive, some will say. In
other words, we tend to think of some sort of
movement, either growth-related or not, as
common evidence for being alive. But a plant
that is not visibly growing is still alive, and
some animals can breathe without visible
movement. So using visible movement as the
dening characteristic of life is not enough.
Movements over very small scales will
be invisible to the naked eye – movements of
molecules, for example. Is this invisible
molecular movement necessary for life? If we
ask this question to professional biologists,
they will say yes. In fact, viruses do not show
any molecular movement in them (until they
infect some cell), and that is partly why there is
a controversy about whether they are truly alive
or not.
Why are molecular movements needed
for life? We have seen in earlier classes that
living organisms are well-organised structures;
they can have tissues, tissues have cells, cells
have smaller components in them, and so on.
Because of the effects of the environment, this
organised, ordered nature of living structures is
very likely to keep breaking down over time. If
order breaks down, the organism will no longer
be alive. So living creatures must keep
repairing and maintaining their structures.
Since all these structures are made up of
molecules, they must move molecules around
all the time.
What are the maintenance processes in
living organisms?Let us explore.
5.1 WHAT ARE LIFE PROCESSES?
The maintenance functions of living
organisms must go on even when they are not
doing anything particular. Even when we are
just sitting in class, even if we are just asleep,
this maintenance job has to go on. The
processes which together perform this
maintenance job are life processes.
Since these maintenance processes are
needed to prevent damage and break-down,
energy is needed for them. This energy comes
from outside the body of the individual
organism. So there must be a process to transfer
a source of energy from outside the body of the
organism, which we call food, to the inside, a
process we commonly call nutrition. If the body
size of the organisms is to grow, additional raw
material will also be needed from outside.
Since life on earth depends on carbon-based
molecules, most of these food sources are also
carbon-based. Depending on the complexity of
these carbon sources, different organisms can
then use different kinds of nutritional
processes.
The outside sources of energy could be
quite varied, since the environment is not under
the control of the individual organism. These
sources of energy, therefore, need to be broken
down or built up in the body, and must be nally
converted to a uniform source of energy that
can be used for the various molecular
movements needed for maintaining living
structures, as well as to the kind of molecules
the body needs to grow. For this, a series of
chemical reactions in the body are necessary.
Oxidising-reducing reactions are some of the
most common chemical means to break-down
molecules. For this, many organisms use
oxygen sourced from outside the body. The
process of acquiring oxygen from outside the
body, and to use it in the process of break-down
of food sources for cellular needs, is what we
call respiration.
In the case of a single-celled organism,
no specic organs for taking in food, exchange
of gases or removal of wastes may be needed
because the entire surface of the organism is in
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
6 7
contact with the environment. But what
happens when the body size of the organism
increases and the body design becomes more
complex? In multi-cellular organisms, all the
cells may not be in direct contact with the
surrounding environment. Thus, simple
diffusion will not meet the requirements of all
the cells.
We have seen previously how, in multi-
cellular organisms, various body parts have
specialised in the functions they perform. We
are familiar with the idea of these specialised
tissues, and with their organisation in the body
of the organism. It is therefore not surprising
that the uptake of food and of oxygen will also
be the function of specialised tissues. However,
this poses a problem, since the food and oxygen
are now taken up at one place in the body of the
organisms, while all parts of the body need
them. This situation creates a need for a
transportation system for carrying food and
oxygen from one place to another in the body.
When chemical reactions use the carbon
source and the oxygen for energy generation,
they create by-products that are not only
useless for the cells of the body, but could even
be harmful. These waste by-products are
therefore needed to be removed from the body
and discarded outside by a process called
excretion. Again, if the basic rules for body
design in multi-cellular organisms are
followed, a specialised tissue for excretion will
be developed, which means that the
transportation system will need to transport
waste away from cells to this excretory tissue.
Let us consider these various processes,
so essential to maintain life, one by one.
1.Why is diffusion insufcient to meet the
oxygen requirements of multi-cellular
organisms like humans?
2.What criteria do we use to decide whether
something is alive?
3.What are outside raw materials used for by
an organism?
4.What processes would you consider
essential for maintaining life?
5.2 NUTRITION
When we walk or ride a bicycle, we are
using up energy. Even when we are not doing
any apparent activity, energy is needed to
maintain a state of order in our body. We also
need materials from outside in order to grow,
develop, synthesise protein and other
substances needed in the body. This source of
energy and materials is the food we eat.
How do living things get their food?
The general requirement for energy and
materials is common in all organisms, but it is
fullled in different ways. Some organisms use
simple food material obtained from inorganic
sources in the form of carbon dioxide and
water. These organisms, the autotrophs, include
green plants and some bacteria. Other
organisms utilise complex substances. These
complex substances have to be broken down
into simpler ones before they can be used for
the upkeep and growth of the body. To achieve
this, organisms use bio-catalysts called
enzymes. Thus, the heterotrophs survival
depends directly or indirectly on autotrophs.
Heterotrophic organisms include animals and
fungi.
5.2.1 Autotrophic Nutrition
Carbon and energy requirements of the
autotrophic organism are fullled by
photosynthesis. It is the process by which
autotrophs take in substances from the outside
and convert them into stored forms of energy.
This material is taken in the form of carbon
dioxide and water which is converted into
carbohydrates in the presence of sunlight and
chlorophyll. Carbohydrates are utilised for
providing energy to the plant. We will study
how this takes place in the next section. The
carbohydrates which are not used immediately
are stored in the form of starch, which serves as
the internal energy reserve to be used as and
when required by the plant. A somewhat similar
situation is seen in us where some of the energy
derived from the food we eat is stored in our
body in the form of glycogen.
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
8 9
Let us now see what actually happens during
the process of photosynthesis. The following
events occur during this process –
(I) Absorption of light energy by
chlorophyll.
(ii) Conversion of light energy to
chemical energy and splitting of water
molecules into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to
carbohydrates.
These steps need not take place one after
the other immediately. For example, desert
plants take up carbon dioxide at night and
prepare an intermediate which is acted upon by
the energy absorbed by the chlorophyll during
the day.
Let us see how each of the components
of the above reaction are necessary for
photosynthesis.
If you carefully observe a cross-section of
a leaf under the microscope (shown in Fig. 5.1),
you will notice that some cells contain green dots.
These green dots are cell organelles called
chloroplasts which contain chlorophyll. Let us do
an activity which demonstrates that chlorophyll
is essential for photosynthesis.
Activity 5.1
gTake a potted plant with variegated leaves
– for example, money plant or crotons.
gKeep the plant in a dark room for three
days so that all the starch gets used up.
gNow keep the plant in sunlight for about
six hours.
gPluck a leaf from the plant. Mark the green
areas in it and trace them on a sheet of
paper.
gDip the leaf in boiling water for a few
minutes.
gAfter this, immerse it in a beaker
containing alcohol.
gCarefully place the above beaker in a
water-bath and heat till the alcohol begins
to boil.
gWhat happens to the colour of the leaf?
What is the colour of the solution?
gNow dip the leaf in a dilute solution of
iodine for a few minutes.
gTake out the leaf and rinse off the iodine
solution.
gObserve the colour of the leaf and
compare this with the tracing of the leaf
done in the beginning (Fig. 5.2).
gWhat can you conclude about the presence
of starch in various areas of the leaf?
(a)
(b)
Now, let us study how the plant obtains carbon
dioxide. In Class IX, we had talked about stomata
(Fig. 5.3) which are tiny pores present on the
surface of the leaves. Massive amounts of
gaseous exchange takes place in the leaves
through these pores for the purpose of
photosynthesis. But it is important to note here
that exchange of gases occurs across the surface
of stems, roots and leaves as well. Since large
amounts of water can also be lost through these
stomata, the plant closes these pores when it does
Figure 5.2 Variegated leaf
(a) before and (b) after starch test
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
10 11
Activity 5.2
gTake two healthy potted plants which are
nearly the same size.
gKeep them in a dark room for three days.
gNow place each plant on separate glass
plates. Place a watch-glass containing
potassium hydroxide by the side of one
of the plants. The potassium hydroxide
is used to absorb carbon dioxide.
gCover both plants with separate bell-jars
as shown in Fig. 5.4.
gUse vaseline to seal the bottom of the
jars to the glass plates so that the set-up is
air-tight.
gKeep the plants in sunlight for about two
hours.
gPluck a leaf from each plant and check
for the presence of starch as in the above
activity.
gDo both the leaves show the presence of
the same amount of starch?
gWhat can you conclude from this
activity?
not need carbon dioxide for photosynthesis. The
opening and closing of the pore is a function of
the guard cells. The guard cells swell when water
ows into them, causing the stomatal pore to
open. Similarly the pore closes if the guard cells
shrink.
Based on the two activities performed above, can
we design an experiment to demonstrate that
sunlight is essential for photosynthesis?
So far, we have talked about how autotrophs
meet their energy requirements. But they also
need other raw materials for building their body.
Water used in photosynthesis is taken up from the
soil by the roots in terrestrial plants. Other
materials like nitrogen, phosphorus, iron and
magnesium are taken up from the soil. Nitrogen
is an essential element used in the synthesis of
proteins and other compounds. This is taken up
in the form of inorganic nitrates or nitrites. Or it is
taken up as organic compounds which have been
prepared by bacteria from atmospheric nitrogen.
5.2.2 Heterotrophic Nutrition
Each organism is adapted to its environment.
The form of nutrition differs depending on the
type and availability of food material as well as
how it is obtained by the organism. For
example, whether the food source is stationary
(such as grass) or mobile (such as a deer),
would allow for differences in how the food is
accessed and what is the nutritive apparatus
used by a cow and a lion. There is a range of
strategies by which the food is taken in and
used by the organism. Some organisms break-
down the food material outside the body and
then absorb it. Examples are fungi like bread
moulds, yeast and mushrooms. Others take in
whole material and break it down inside their
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
12 13
Figure 5.5
Nutrition in Amoeba
bodies. What can be taken in and broken down
depends on the body design and functioning.
Some other organisms derive nutrition from
plants or animals without killing them. This
parasitic nutritive strategy is used by a wide
variety of organisms like cuscuta (amar-bel),
ticks, lice, leeches and tape-worms.
5.2.3 How do Organisms obtain their
Nutrition?
Since the food and the way it is obtained differ,
the digestive system is different in various
organisms. In single-celled organisms, the food
may be taken in by the entire surface. But as the
complexity of the organism increases, different
parts become specialised to perform different
functions. For example, Amoeba takes in food
using temporary nger-like extensions of the
cell surface which fuse over the food particle
forming a food-vacuole (Fig. 5.5). Inside the
food-vacuole, complex substances are broken
down into simpler ones which then diffuse into
the cytoplasm. The remaining undigested
material is moved to the surface of the cell and
thrown out. In Paramoecium, which is also a
unicellular organism, the cell has a denite
shape and food is taken in at a specic spot.
Food is moved to this spot by the movement of
cilia which cover the entire surface of the cell.
5.2.4 Nutrition in Human Beings
The alimentary canal is basically a long tube
extending from the mouth to the anus. In Fig.
5.6, we can see that the tube has different parts.
Various regions are specialised to perform
different functions. What happens to the food
once it enters our body? We shall discuss this
process here.
Activity 5.3
gTake 1 mL starch solution (1%) in two test
tubes (A and B).
gAdd 1 mL saliva to test tube A and leave
both test tubes undisturbed for 20-30
minutes.
gNow add a few drops of dilute iodine
solution to the test tubes.
gIn which test tube do you observe a colour
change?
gWhat does this indicate about the
presence or absence of starch in the two
test tubes?
gWhat does this tell us about the action of
saliva on starch?
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
14 15
We eat various types of food which has to pass
through the same digestive tract. Naturally the
food has to be processed to generate particles
which are small and of the same texture. This is
achieved by crushing the food with our teeth.
Since the lining of the canal is soft, the food is
also wetted to make its passage smooth. When
we eat something we like, our mouth ‘waters’.
This is actually not only water, but a uid called
saliva secreted by the salivary glands. Another
aspect of the food we ingest is its complex
nature. If it is to be absorbed from the
alimentary canal, it has to be broken into
smaller molecules. This is done with the help of
biological catalysts called enzymes. The saliva
contains an enzyme called salivary amylase
that breaks down starch which is a complex
molecule to give simple sugar. The food is
mixed thoroughly with saliva and moved
around the mouth while chewing by the
muscular tongue.
It is necessary to move the food in a
regulated manner along the digestive tube so
that it can be processed properly in each part.
The lining of canal has muscles that contract
rhythmically in order to push the food forward.
These peristaltic movements occur all along the
gut.
From the mouth, the food is taken to the
stomach through the food-pipe or oesophagus.
The stomach is a large organ which expands
when food enters it. The muscular walls of the
stomach help in mixing the food thoroughly
with more digestive juices.
The digestion in stomach is taken care of
by the gastric glands present in the wall of the
stomach. These release hydrochloric acid, a
protein digesting enzyme called pepsin, and
mucus. The hydrochloric acid creates an acidic
medium which facilitates the action of the
enzyme pepsin. What other function do you
think is served by the acid? The mucus protects
the inner lining of the stomach from the action
of the acid under normal conditions. We have
often heard adults complaining about ‘acidity’.
Can this be related to what has been discussed
above?
The exit of food from the stomach is
regulated by a sphincter muscle which releases
it in small amounts into the small intestine.
From the stomach, the food now enters the
small intestine. This is the longest part of the
alimentary canal which is tted into a compact
space because of extensive coiling. The length
of the small intestine differs in various animals
depending on the food they eat. Herbivores
eating grass need a longer small intestine to
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€dŸ«Å£”VŸäsÁ+

ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
16 17
The small intestine is the site of the
complete digestion of carbohydrates, proteins
and fats. It receives the secretions of the liver
and pancreas for this purpose. The food coming
from the stomach is acidic and has to be made
alkaline for the pancreatic enzymes to act. Bile
juice from the liver accomplishes this in
addition to acting on fats. Fats are present in the
intestine in the form of large globules which
makes it difcult for enzymes to act on them.
Bile salts break them down into smaller
globules increasing the efciency of enzyme
action. This is similar to the emulsifying action
of soaps on dirt that we have learnt about in
Chapter 4. The pancreas secretes pancreatic
juice which contains enzymes like trypsin for
digesting proteins and lipase for breaking down
emulsied fats. The walls of the small intestine
contain glands which secrete intestinal juice.
The enzymes present in it nally convert the
proteins to amino acids, complex
carbohydrates into glucose and fats into fatty
acids and glycerol.
Digested food is taken up by the walls of
the intestine. The inner lining of the small
intestine has numerous nger-like projections
called villi which increase the surface area for
absorption. The villi are richly supplied with
blood vessels which take the absorbed food to
each and every cell of the body, where it is
utilised for obtaining energy, building up new
tissues and the repair of old tissues.
The unabsorbed food is sent into the
large intestine where its wall absorb more water
from this material. The rest of the material is
removed from the body via the anus. The exit of
this waste material is regulated by the anal
sphincter.
More to Know!
Dental caries
Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins when
bacteria acting on sugars produce acids that softens or demineralises the enamel. Masses of
bacterial cells together with food particles stick to the teeth to form dental plaque. Saliva cannot
reach the tooth surface to neutralise the acid as plaque covers the teeth. Brushing the teeth after
eating removes the plaque before the bacteria produce acids. If untreated, microorganisms may
invade the pulp, causing inammation and infection.
Activity 5.4
1. What are the differences between
autotrophic nutrition and heterotrophic
nutrition?
2. Where do plants get each of the raw
materials required for photosynthesis?
3. What is the role of the acid in our
stomach?
4. What is the function of digestive
enzymes?
5. How is the small intestine designed to
absorb digested food?
gTake some freshly prepared lime water in
a test tube.
gBlow air through this lime water.
gNote how long it takes for the lime water
to turn milky.
gUse a syringe or pichkari to pass air
through some fresh lime water taken in
another test tube (Fig. 5.7).
gNote how long it takes for this lime water
to turn milky.
gWhat does this tell us about the amount of
carbon dioxide in the air that we breathe
out?
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allow the cellulose to be digested. Meat is
easier to digest, hence carnivores like tigers
have a shorter small intestine.
5.3 RESPIRATION

ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
18 19
Activity 5.5
gTake some fruit juice or sugar solution
and add some yeast to this. Take this
mixture in a test tube tted with a one-
holed cork.
gFit the cork with a bent glass tube. Dip the
free end of the glass tube into a test tube
containing freshly prepared lime water.
gWhat change is observed in the lime
water and how long does it take for this
change to occur?
gWhat does this tell us about the products
of fermentation?
We have discussed nutrition in
organisms in the last section. The food material
taken in during the process of nutrition is used
in cells to provide energy for various life
processes. Diverse organisms do this in
different ways – some use oxygen to break-
down glucose completely into carbon dioxide
and water, some use other pathways that do not
involve oxygen (Fig. 5.8). In all cases, the rst
step is the break-down of glucose, a six-carbon
molecule, into a three-carbon molecule called
pyruvate. This process takes place in the
cytoplasm. Further, the pyruvate may be
converted into ethanol and carbon dioxide. This
process takes place in yeast during
fermentation. Since this process takes place in
the absence of air (oxygen), it is called
anaerobic respiration. Break- down of pyruvate
using oxygen takes place in the mitochondria.
This process breaks up the three-carbon
pyruvate molecule to give three molecules of
carbon dioxide. The other product is water.
Since this process takes place in the presence of
air (oxygen), it is called aerobic respiration.
The release of energy in this aerobic process is a
lot greater than in the anaerobic process.
Sometimes, when there is a lack of oxygen in
our muscle cells, another pathway for the
break-down of pyruvate is taken. Here the
pyruvate is converted into lactic acid which is
also a three-carbon molecule. This build-up of
lactic acid in our muscles during sudden
activity causes cramps.
Figure 5.8
Break-down of glucose by various pathways
Figure 5.7
(a) Air being passed into lime water with a pichkari/
syringe, (b) air being exhaled into lime water
The energy released during cellular
respiration is immediately used to synthesise a
molecule called ATP which is used to fuel all
other activities in the cell. In these processes,
ATP is broken down giving rise to a xed
amount of energy which can drive the
endothermic reactions taking place in the cell.
ATP : ATP is the energy currency for most cellular processes. The energy released during the
process of respiration is used to make an ATP molecule from ADP and inorganic phosphate.
More to Know!
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
20 21
Endothermic processes in the cell then use this ATP to drive the reactions. When the terminal phosphate
linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released.
Think of how a battery can provide energy for many different kinds of uses. It can be used to obtain
mechanical energy, light energy, electrical energy and so on. Similarly, ATP can be used in the cells for
the contraction of muscles, protein synthesis, conduction of nervous impulses and many other activities.
Since the aerobic respiration pathway
depends on oxygen, aerobic organisms need to
ensure that there is sufcient intake of oxygen.
We have seen that plants exchange gases
through stomata, and the large inter-cellular
spaces ensure that all cells are in contact with
air. Carbon dioxide and oxygen are exchanged
by diffusion here. They can go into cells, or
away from them and out into the air. The
direction of diffusion depends upon the
environmental conditions and the requirements
of the plant. At night, when there is no
photosynthesis occurring, CO2 elimination is
the major exchange activity going on. During
the day, CO2 generated during respiration is
used up for photosynthesis, hence there is no
CO2 release. Instead, oxygen release is the
major event at this time.
Animals have evolved different organs
for the uptake of oxygen from the environment
and for getting rid of the carbon dioxide
produced. Terrestrial animals can breathe the
oxygen in the atmosphere, but animals that live
in water need to use the oxygen dissolved in
water.
Activity 5.6
gObserve sh in an aquarium. They open
and close their mouths and the gill-slits
(or the operculum which covers the gill-
slits) behind their eyes also open and
close. Are the timings of the opening and
closing of the mouth and gill-slits
coordinated in some manner?
gCount the number of times the sh opens
and closes its mouth in a minute.
gCompare this to the number of times you
breathe in and out in a minute.
Since the amount of dissolved oxygen is
fairly low compared to the amount of oxygen in
the air, the rate of breathing in aquatic organisms
is much faster than that seen in terrestrial
organisms. Fishes take in water through their
mouths and force it past the gills where the
dissolved oxygen is taken up by blood.
Terrestrial organisms use the oxygen in
the atmosphere for respiration. This oxygen is
absorbed by different organs in different
animals. All these organs have a structure that
increases the surface area which is in contact
with the oxygen-rich atmosphere. Since the
exchange of oxygen and carbon dioxide has to
take place across this surface, this surface is
very ne and delicate. In order to protect this
surface, it is usually placed within the body, so
there have to be passages that will take air to
this area. In addition, there is a mechanism for
moving the air in and out of this area where the
oxygen is absorbed.
In human beings (Fig. 5.9), air is taken
into the body through the nostrils. The air
passing through the nostrils is ltered by ne
hairs that line the passage. The passage is also
lined with mucus which helps in this process.
From here, the air passes through the throat and
into the lungs. Rings of cartilage are present in
the throat. These ensure that the air-passage
does not collapse.
More to Know!
gUsing tobacco directly or any product of tobacco in the form of cigar, cigarettes, bidis,
hookah, gutkha, etc., is harmful. Use of tobacco most commonly affects the tongue, lungs,
heart and liver. Smokeless tobacco is also a major risk factor for heart attacks, strokes,
pulmonary diseases and several forms of cancers. There is a high incidence of oral cancer in
India due to the chewing of tobacco in the form of gutkha. Stay healthy; just say NO to tobacco
and its products!
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
22 23
Within the lungs, the passage divides
into smaller and smaller tubes which nally
terminate in balloon-like structures which are
called alveoli (singular–alveolus). The alveoli
provide a surface where the exchange of gases
can take place. The walls of the alveoli contain
an extensive network of blood-vessels. As we
have seen in earlier years, when we breathe in,
we lift our ribs and atten our diaphragm, and
the chest cavity becomes larger as a result.
Because of this, air is sucked into the lungs and
lls the expanded alveoli. The blood brings
carbon dioxide from the rest of the body for
release into the alveoli, and the oxygen in the
alveolar air is taken up by blood in the alveolar
blood vessels to be transported to all the cells in
the body. During the breathing cycle, when air
Figure 5.9 Human respiratory system
is taken in and let out, the lungs always contain
a residual volume of air so that there is
sufcient time for oxygen to be absorbed and
for the carbon dioxide to be released.
When the body size of animals is large,
the diffusion pressure alone cannot take care of
oxygen delivery to all parts of the body. Instead,
respiratory pigments take up oxygen from the
air in the lungs and carry it to tissues which are
decient in oxygen before releasing it. In
human beings, the respiratory pigment is
haemoglobin which has a very high afnity for
oxygen. This pigment is present in the red
blood corpuscles. Carbon dioxide is more
soluble in water than oxygen is and hence is
mostly transported in the dissolved form in our
blood.
Do you Know!
Smoking is injurious to health.
Lung cancer is one of common causes of deaths in the world. The upper part of respiratory tract
is provided with small hair-like structures called cilia. These cilia help to remove germs, dust
and other harmful particles from inhaled air. Smoking destroys these hair due to which germs,
dust, smoke and other harmful chemicals enter lungs and cause infection, cough and even lung
cancer.
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g If the alveolar surface were spread out, it would cover about 80 m2. How much do you think
the surface area of your body is? Consider how efcient exchange of gases becomes because
of the large surface available for the exchange to take place.
g If diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a
molecule of oxygen to get to our toes from our lungs. Aren’t you glad that we have
haemoglobin?
1. What advantage over an aquatic organism does a terrestrial organism have with regard to
obtaining oxygen for respiration?
2. What are the different ways in which glucose is oxidised to provide energy in various
organisms?
3. How is oxygen and carbon dioxide transported in human beings?
4. How are the lungs designed in human beings to maximise the area for exchange of gases?
5.4 TRANSPORTATION
5.4.1 Transportation in Human Beings
Activity 5.7
gVisit a health centre in your locality and
nd out what is the normal range of
haemoglobin content in human beings.
gIs it the same for children and adults?
gIs there any difference in the
haemoglobin levels for men and women?
gVisit a veterinary clinic in your locality.
Find out what is the normal range of
haemoglobin content in an animal like
the buffaloor cow.
gIs this content different in calves, male
and female animals?
gCompare the difference seen in male and
female human beings and animals.
gHow would the difference, if any, be
explained?
We have seen in previous sections that
blood transports food, oxygen and waste
materials in our bodies. In Class IX, we learnt
about blood being a uid connective tissue.
Blood consists of a uid medium called plasma
in which the cells are suspended. Plasma
transports food, carbon dioxide and
nitrogenous wastes in dissolved form. Oxygen
is carried by the red blood corpuscles. Many
other substances like salts, are also transported
by the blood. We thus need a pumping organ to
push blood around the body, a network of tubes
to reach all the tissues and a system in place to
ensure that this network can be repaired if
damaged.
Our pump — the heart
The heart is a muscular organ which is as big as
our st (Fig. 5.10). Because both oxygen and
carbon dioxide have to be transported by the
blood, the heart has different chambers to
prevent the oxygen-rich blood from mixing
with the blood containing carbon dioxide. The
carbon dioxide-rich blood has to reach the
lungs for the carbon dioxide to be removed, and
the oxygenated blood from the lungs has to be
brought back to the heart. This oxygen-rich
blood is then pumped to the rest of the body.
We can follow this process step by step
(Fig. 5.11). Oxygen-rich blood from the lungs
comes to the thin-walled upper chamber of the
heart on the left, the left atrium. The left atrium
relaxes when it is collecting this blood. It then
contracts, while the next chamber, the left
ventricle, relaxes, so that the blood is
transferred to it. When the muscular left
Figure 5.10
Schematic sectional view of the human heart

ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
26 27
ventricle contracts in its turn, the blood is
pumped out to the body. De-oxygenated blood
comes from the body to the upper chamber on
the right, the right atrium, as it relaxes. As the
right atrium contracts, the corresponding lower
chamber, the right ventricle, dilates. This
transfers blood to the right ventricle, which in
turn pumps it to the lungs for oxygenation.
Since ventricles have to pump blood into
various organs, they have thicker muscular
walls than the atria do. Valves ensure that blood
does not ow backwards when the atria or
ventricles contract.
Oxygen enters the blood in the lungs
The separation of the right side and the left side
of the heart is useful to keep oxygenated and de-
oxygenated blood from mixing. Such
separation allows a highly efcient supply of
oxygen to the body. This is useful in animals
that have high energy needs, such as birds and
mammals, which constantly use energy to
maintain their body temperature. In animals
that do not use energy for this purpose, the body
temperature depends on the temperature in the
environment. Such animals, like amphibians or
many reptiles have three-chambered hearts,
and tolerate some mixing of the oxygenated
and de-oxygenated blood streams. Fishes, on
the other hand, have only two chambers to their
hearts, and the blood is pumped to the gills, is
oxygenated there, and passes directly to the rest
of the body. Thus, blood goes only once
through the heart in the sh during one cycle of
passage through the body. On the other hand, it
goes through the heart twice during each cycle
in other vertebrates. This is known as double
circulation.
More to Know!
Blood pressure
The force that blood exerts against the wall of a vessel is called blood pressure. This pressure is
much greater in arteries than in veins. The pressure of blood inside the artery during ventricular
systole (contraction) is called systolic pressure and pressure in artery during ventricular diastole
(relaxation) is called diastolic pressure. The normal systolic pressure is about 120 mm of Hg and
diastolic pressure is 80 mm of Hg.
Blood pressure is measured with an instrument called sphygmomanometer. High blood pressure
is also called hypertension and is caused by the constriction of arterioles, which results in
increased resistance to blood ow. It can lead to the rupture of an artery and internal bleeding.
Figure 5.11
Schematic representation of transport and
exchange of oxygen and carbon dioxide
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
28 29
The tubes – blood vessels
Arteries are the vessels which carry
blood away from the heart to various organs of
the body. Since the blood emerges from the
heart under high pressure, the arteries have
thick, elastic walls. Veins collect the blood from
different organs and bring it back to the heart.
They do not need thick walls because the blood
is no longer under pressure, instead they have
valves that ensure that the blood ows only in
one direction.
On reaching an organ or tissue, the
artery divides into smaller and smaller vessels
to bring the blood in contact with all the
individual cells. The smallest vessels have
walls which are one-cell thick and are called
capillaries. Exchange of material between the
blood and surrounding cells takes place across
this thin wall. The capillaries then join together
to form veins that convey the blood away from
the organ or tissue.
Maintenance by platelets
What happens if this system of tubes develops a
leak? Think about situations when we are
injured and start bleeding. Naturally the loss of
blood from the system has to be minimised. In
addition, leakage would lead to a loss of
pressure which would reduce the efciency of
the pumping system. To avoid this, the blood
has platelet cells which circulate around the
body and plug these leaks by helping to clot the
blood at these points of injury.
Lymph
There is another type of uid also involved in
transportation. This is called lymph or tissue
uid. Through the pores present in the walls of
capillaries some amount of plasma, proteins
and blood cells escape into intercellular spaces
in the tissues to form the tissue uid or lymph. It
is similar to the plasma of blood but colourless
and contains less protein. Lymph drains into
lymphatic capillaries from the intercellular
spaces, which join to form large lymph vessels
that nally open into larger veins. Lymph
carries digested and absorbed fat from intestine
and drains excess uid from extra cellular
space back into the blood.
5.4.2 Transportation in Plants
We have discussed earlier how plants take in
simple compounds such as CO2 and
photosynthesise energy stored in their
chlorophyll-containing organs, namely leaves.
The other kinds of raw materials needed for
building plant bodies will also have to be taken
up separately. For plants, the soil is the nearest
and richest source of raw materials like
nitrogen, phosphorus and other minerals. The
absorption of these substances therefore occurs
through the part in contact with the soil, namely
roots. If the distances between soil-contacting
organs and chlorophyll-containing organs are
small, energy and raw materials can easily
diffuse to all parts of the plant body. But if these
distances become large because of changes in
plant body design, diffusion processes will not
be sufcient to provide raw material in leaves
and energy in roots. A proper system of
transportation is therefore essential in such
situations.
Energy needs differ between different
body designs. Plants do not move, and plant
bodies have a large proportion of dead cells in
many tissues. As a result, plants have low
energy needs, and can use relatively slow
transport systems. The distances over which
transport systems have to operate, however, can
be very large in plants such as very tall trees.
Plant transport systems will move
energy stores from leaves and raw materials
from roots. These two pathways are
constructed as independently organised
conducting tubes. One, the xylem moves water
and minerals obtained from the soil. The other,
phloem transports products of photosynthesis
from the leaves where they are synthesised to
other parts of the plant. We have studied the
structure of these tissues in detail in Class IX.
Transport of water
In xylem tissue, vessels and tracheids of the
roots, stems and leaves are interconnected to
form a continuous system of water-conducting
channels reaching all parts of the plant. At the
roots, cells in contact with the soil actively take
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
30 31
¿£Ôá«+5.8Activity 5.8
gTake two small pots of approximately
the same size and having the same
amount of soil. One should have a plant
in it. Place a stick of the same height as
the plant in the other pot.
gCover the soil in both pots with a plastic
sheet so that moisture cannot escape by
evaporation.
gCover both sets, one with the plant and
the other with the stick, with plastic
sheets and place in bright sunlight for
half an hour.
gDo you observe any difference in the
two cases?
Provided that the plant has an adequate
supply of water, the water which is lost through
the stomata is replaced by water from the xylem
vessels in the leaf. In fact, evaporation of water
molecules from the cells of a leaf creates a
suction which pulls water from the xylem cells
of roots. The loss of water in the form of vapour
from the aerial parts of the plant is known as
transpiration.
Thus, transpiration helps in the absorption and
upward movement of water and minerals
dissolved in it from roots to the leaves. It also
helps in temperature regulation. The effect of
root pressure in transport of water is more
important at night. During the day when the
stomata are open, the transpiration pull
becomes the major driving force in the
movement of water in the xylem.
Transport of food and other substances
So far we have discussed the transport of water
and minerals in plants. Now let us consider how
the products of metabolic processes,
particularly photosynthesis, are moved from
leaves, where they are formed, to other parts of
the plant. This transport of soluble products of
photosynthesis is called translocation and it
occurs in the part of the vascular tissue known
as phloem. Besides the products of
photosynthesis, the phloem transports amino
acids and other substances. These substances
are especially delivered to the storage organs of
roots, fruits and seeds and to growing organs.
The translocation of food and other substances
takes place in the sieve tubes with the help of
adjacent companion cells both in upward and
downward directions.
Unlike transport in xylem which can be largely
explained by simple physical forces, the
translocation in phloem is achieved by utilising

energy. Material like sucrose is transferred into
phloem tissue using energy from ATP. This
increases the osmotic pressure of the tissue
causing water to move into it. This pressure
moves the material in the phloem to tissues
which have less pressure. This allows the
phloem to move material according to the
plant’s needs. For example, in the spring, sugar
stored in root or stem tissue would be
transported to the buds which need energy to
grow.
Figure 5.12
Movement of water during
transpiration in a tree
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up ions. This creates a difference in the
concentration of these ions between the root
and the soil. Water, therefore,moves into the
root from the soil to eliminate this difference.
This means that there is steady movement of
water into root xylem, creating a column of
water that is steadily pushed upwards.
However, this pressure by itself is
unlikely to be enough to move water over the
heights that we commonly see in plants. Plants
use another strategy to move water in the xylem
upwards to the highest points of the plant body.
–

ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
32 33
Figure 5.13
Excretory system in human beings Figure 5.14
Structure of a nephron
We have already discussed how organisms get
rid of gaseous wastes generated during
photosynthesis or respiration. Other metabolic
activities generate nitrogenous materials which
need to be removed. The biological process
involved in the removal of these harmful
metabolic wastes from the body is called
excretion. Different organisms use varied
strategies to do this. Many unicellular
organisms remove these wastes by simple
diffusion from the body surface into the
surrounding water. As we have seen in other
processes, complex multi-cellular organisms
use specialised organs to perform the same
function.
like in the lungs, is a cluster of very thin-walled
blood capillaries. Each capillary cluster in the
kidney is associated with the cup-shaped end of
a coiled tube called Bowman’s capsule that
collects the ltrate (Fig. 5.14). Each kidney has
large numbers of these ltration units called
nephrons packed close together. Some
substances in the initial ltrate, such as glucose,
amino acids, salts and a major amount of water,
are selectively re-absorbed as the urine ows
along the tube. The amount of water re-
absorbed depends on how much excess water
there is in the body, and on how much of
dissolved waste there is to be excreted. The
urine forming in each kidney eventually enters
5.5.1 Excretion in Human Beings
The excretory system of human beings (Fig.
5.13) includes a pair of kidneys, a pair of
ureters, a urinary bladder and a urethra.
Kidneys are located in the abdomen, one on
either side of the backbone. Urine produced in
the kidneys passes through the ureters into the
urinary bladder where it is stored until it is
released through the urethra.
How is urine produced? The purpose of making
urine is to lter out waste products from the
blood. Just as CO is removed from the blood in
2
the lungs, nitrogenous waste such as urea or
uric acid are removed from blood in the
kidneys. It is then no surprise that the basic
ltration unit in the kidneys,
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1. What are the components of the transport
system in human beings? What are the
functions of these components?
2. Why is it necessary to separate
oxygenated and deoxygenated blood in
mammals and birds?
3. What are the components of the transport
system in highly organised plants?
4. How are water and minerals transported in
plants?
5. How is food transported in plants?
5.5 EXCRETION

ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
34 35
a long tube, the ureter, which connects the
kidneys with the urinary bladder. Urine is
stored in the urinary bladder until the pressure
of the expanded bladder leads to the urge to
More to Know!
Articial kidney (Hemodialysis)
Kidneys are vital organs for survival. Several factors
like infections, injury or restricted blood ow to kidneys
reduce the activity of kidneys. This leads to
accumulation of poisonous wastes in the body, which
can even lead to death. In case of kidney failure, an
articial kidney can be used. An articial kidney is a
device to remove nitrogenous waste products from the
blood through dialysis.
Articial kidneys contain a number of tubes with a semi-
permeable lining, suspended in a tank lled with
dialysing uid. This uid has the same osmotic pressure
as blood, except that it is devoid of nitrogenous wastes.
The patient’s blood is passed through these tubes.
During this passage, the waste products from the blood pass into dialysing uid by diffusion. The
puried blood is pumped back into the patient. This is similar to the function of the kidney, but it is
different since there is no re-absorption involved. Normally, in a healthy adult, the initial ltrate
in the kidneys is about 180 L daily. However, the volume actually excreted is only a litre or two a
day, because the remaining ltrate is re-absorbed in the kidney tubules.
Think it over!
Organ donation
Organ donation is a generous act of donating
an organ to a person who suffers from non-
function of organ(s). Donation of an organ
may be done by the consent of the donor and
his/her family. Anyone regardless of age or
gender can become an organ and tissue donor.
Organ transplants can save or transform the
life of a person. Transplantation is required
because recipient’s organ has been damaged
or has failed by disease or injury. In organ
transplantation the organ is surgically
removed from one person (organ donor) and
transplanted to another person (the recipient).
Common transplantations include corneas,
kidneys, heart, liver, pancreas, lungs,
intestines and bone marrow. Most organ and
tissue donations occur just after the donor has
pass it out through the urethra. The bladder is
muscular, so it is under nervous control, as we
have discussed elsewhere. As a result, we can
usually control the urge to urinate.
5.5.2 Excretion in Plants
Plants use completely different strategies for
excretion than those of animals. Oxygen itself
can be thought of as a waste product generated
during photosynthesis! We have discussed
earlier how plants deal with oxygen as well as
CO2. They can get rid of excess water by
transpiration. For other wastes, plants use the
fact that many of their tissues consist of dead
cells, and that they can even lose some parts
such as leaves. Many plant waste products are
stored in cellular vacuoles. Waste products may
be stored in leaves that fall off. Other waste
products are stored as resins and gums,
especially in old xylem. Plants also excrete
some waste substances into the soil around
them.
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died or when the doctor declares a person
brain dead. But some organs such as kidney,
part of a liver, lung, etc., and tissues can be
donated while the donor is alive.
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
36 37
1. Describe the structure and functioning of nephrons.
2. What are the methods used by plants to get rid of
excretory products?
3. How is the amount of urine produced regulated?
What you have learnt
gMovement of various types can be taken as an indication of life.
gMaintenance of life requires processes like nutrition, respiration, transport of materials
within the body and excretion of waste products.
gAutotrophic nutrition involves the intake of simple inorganic materials from the
environment and using an external energy source like the Sun to synthesise complex high-
energy organic material.
gHeterotrophic nutrition involves the intake of complex material prepared by other
organisms.
gIn human beings, the food eaten is broken down by various steps along the alimentary canal
and the digested food is absorbed in the small intestine to be sent to all cells in the body.
gDuring the process of respiration, organic compounds such as glucose are broken down to
provide energy in the form of ATP. ATP is used to provide energy for other reactions in the
cell.
gRespiration may be aerobic or anaerobic. Aerobic respiration makes more energy available
to the organism.
gIn human beings, the transport of materials such as oxygen, carbon dioxide, food and
excretory products is a function of the circulatory system. The circulatory system consists of
the heart, blood and blood vessels.
gIn highly differentiated plants, transport of water, minerals, food and other materials is a
function of the vascular tissue which consists of xylem and phloem.
gIn human beings, excretory products in the form of soluble nitrogen compounds are
removed by the nephrons in the kidneys.
gPlants use a variety of techniques to get rid of waste material. For example, waste material
may be stored in the cell-vacuoles or as gum and resin, removed in the falling leaves, or
excreted into the surrounding soil.
EXERCISES
1. The kidneys in human beings are a part of the system for
(a) nutrition. (c) excretion.
(b) respiration. (d) transportation.
2. The xylem in plants are responsible for
(a) transport of water. (c) transport of amino acids.
(b) transport of food. (d) transport of oxygen.
3. The autotrophic mode of nutrition requires
(a) carbon dioxide and water. (c) sunlight.
(b) chlorophyll. (d) all of the above.
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ANDHRA PRADESH | Biology : Life Processes €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :Jeç¿ìjáT\T
38 39
4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm. (c) chloroplast.
(b) mitochondria. (d) nucleus.
5. How are fats digested in our bodies? Where does this process take place?
6. What is the role of saliva in the digestion of food?
7. What are the necessary conditions for autotrophic nutrition and what are its by-products?
8. What are the differences between aerobic and anaerobic respiration? Name some organisms
that use the anaerobic mode of respiration.
9. How are the alveoli designed to maximise the exchange of gases?
10. What would be the consequences of a deciency of haemoglobin in our bodies?
11. Describe double circulation of blood in human beings. Why is it necessary?
12. What are the differences between the transport of materials in xylem and phloem?
13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to
their structure and functioning.
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6
Control and
Coordination

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I
n the previous chapter, we looked at
life processes involved in the
maintenance functions in living organisms.
There, we had started with a notion we all have,
that if we see something moving, it is alive.
Some of these movements are in fact the result
of growth, as in plants. A seed germinates and
grows, and we can see that the seedling moves
over the course of a few days, it pushes soil
aside and comes out. But if its growth were to
be stopped, these movements would not
happen. Some movements, as in many animals
and some plants, are not connected with
growth. A cat running, children playing on
swings, buffaloes chewing cud – these are not
movements caused by growth.
Why do we associate such visible
movements with life? A possible answer is that
we think of movement as a response to a change
in the environment of the organism. The cat
may be running because it has seen a mouse.
Not only that, we also think of movement as an
attempt by living organisms to use changes in
their environment to their advantage. Plants
grow out into the sunshine. Children try to get
pleasure and fun out of swinging. Buffaloes
chew cud to help break up tough food so as to be
able to digest it better. When bright light is
focussed on our eyes or when we touch a hot
object, we detect the change and respond to it
with movement in order to protect ourselves.
If we think a bit more about this, it
becomes apparent that all this movement, in
response to the environment, is carefully
controlled. Each kind of a change in the
environment evokes an appropriate movement
in response. When we want to talk to our friends
in class, we whisper, rather than shouting
loudly. Clearly, the movement to be made
depends on the event that is triggering it.
Therefore, such controlled movement must be
connected to the recognition of various events
in the environment, followed by only the
correct movement in response. In other words,
living organisms must use systems providing
control and coordination. In keeping with the
general principles of body organisation in
multicellular organisms, specialised tissues are
used to provide these control and coordination
activities.
6.1 ANIMALS – NERVOUS SYSTEM
In animals, such control and
coordination are provided by nervous and
muscular tissues, which we have studied in
Class IX. Touching a hot object is an urgent and
dangerous situation for us. We need to detect it,
and respond to it. How do we detect that we are
touching a hot object? All information from our
environment is detected by the specialised tips
of some nerve cells. These receptors are usually
located in our sense organs, such as the inner
ear, the nose, the tongue, and so on. So
gustatory receptors will detect taste while
olfactory receptors will detect smell.
This information, acquired at the end of
the dendritic tip of a nerve cell [Fig. 6.1 (a)],
sets off a chemical reaction that creates an
electrical impulse. This impulse travels from
the dendrite to the cell body, and then along the
axon to its end. At the end of the axon, the
electrical impulse sets off the release of some
chemicals. These chemicals cross the gap, or
synapse, and start a similar electrical impulse in
a dendrite of the next neuron. This is a general
|Ÿ³+6.1
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Figure 6.1
(a) Structure of neuron,
(b) Neuromuscular junction
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
44 45
scheme of how nervous impulses travel in the
body. A similar synapse nally allows delivery
of such impulses from neurons to other cells,
such as muscles cells or gland [Fig. 6.1 (b)].
It is thus no surprise that nervous tissue
is made up of an organised network of nerve
cells or neurons, and is specialised for
conducting information via electrical impulses
from one part of the body to another.
Look at Fig. 6.1 (a) and identify the parts
of a neuron (i) where information is acquired,
(ii) through which information travels as an
electrical impulse, and (iii) where this impulse
must be converted into a chemical signal for
onward transmission.
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Activity 6.1
gPut some sugar in your mouth. How does
it taste?
gBlock your nose by pressing it between
your thumb and index nger. Now eat
sugar again. Is there any difference in its
taste?
gWhile eating lunch, block your nose in
the same way and notice if you can fully
appreciate the taste of the food you are
eating.
Is there a difference in how sugar and
food taste if your nose is blocked? If so, why
might this be happening? Read and talk about
possible explanations for these kinds of
differences. Do you come across a similar
situation when you have a cold?
6.1.1 What happens in Reex Actions?
‘Reex’ is a word we use very commonly
when we talk about some sudden action in
response to something in the environment. We
say ‘I jumped out of the way of the bus
reexly’, or ‘I pulled my hand back from the
ame reexly’, or ‘I was so hungry my mouth
started watering reexly’. What exactly do we
mean? A common idea in all such examples is
that we do something without thinking about it,
or without feeling in control of our reactions.
Yet these are situations where we are
responding with some action to changes in our
environment. How is control and coordination
achieved in such situations?
Let us consider this further. Take one of
our examples. Touching a ame is an urgent
and dangerous situation for us, or in fact, for
any animal! How would we respond to this?
One seemingly simple way is to think
consciously about the pain and the possibility
of getting burnt, and therefore move our hand.
An important question then is, how long will it
take us to think all this? The answer depends on
how we think. If nerve impulses are sent
around the way we have talked about earlier,
then thinking is also likely to involve the
creation of such impulses. Thinking is a
complex activity, so it is bound to involve a
complicated interaction of many nerve
impulses from many neurons.
If this is the case, it is no surprise that the
thinking tissue in our body consists of dense
networks of intricately arranged neurons. It sits
in the forward end of the skull, and receives
signals from all over the body which it thinks
about before responding to them. Obviously, in
order to receive these signals, this thinking part
of the brain in the skull must be connected to
nerves coming from various parts of the body.
Similarly, if this part of the brain is to instruct
muscles to move, nerves must carry this signal
back to different parts of the body. If all of this is
to be done when we touch a hot object, it may
take enough time for us to get burnt!
How does the design of the body solve
this problem? Rather than having to think about
the sensation of heat, if the nerves that detect
heat were to be connected to the nerves that
move muscles in a simpler way, the process of
detecting the signal or the input and responding
to it by an output action might be completed
quickly. Such a connection is commonly called
a reex arc (Fig. 6.2). Where should such reex
arc connections be made between the input
nerve and the output nerve? The best place, of
course, would be at the point where they rst
meet each other. Nerves from all over the body
meet in a bundle in the spinal cord on their way
to the brain. Reex arcs are formed in this
spinal cord itself, although the information
input also goes on to reach the brain.
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
46 47
Of course, reex arcs have evolved in
animals because the thinking process of the
brain is not fast enough. In fact many animals
have very little or none of the complex neuron
network needed for thinking. So it is quite
likely that reex arcs have evolved as efcient
ways of functioning in the absence of true
thought processes. However, even after
complex neuron networks have come into
existence, reex arcs continue to be more
efcient for quick responses.
Can you now trace the sequence of events
which occur when a bright light is focussed on
your eyes?
6.1.2 Human Brain
Is reex action the only function of the
spinal cord? Obviously not, since we know that
we are thinking beings. Spinal cord is made up
of nerves which supply information to think
about. Thinking involves more complex
mechanisms Pand neural connections. These
are concentrated in the brain, which is the main
coordinating centre of the body. The brain and
spinal cord constitute the central nervous
system (Fig. 6.3). They receive information
from all parts of the body and integrate it.
We also think about our actions. Writing,
talking, moving a chair, clapping at the end of a
programme are examples of voluntary actions
which are based on deciding what to do next.
So, the brain also has to send messages to
muscles. This is the second way in which the
nervous system communicates with the
Figure 6.2 Reex arc
muscles. The communication between the
central nervous system and the other parts of
the body is facilitated by the peripheral nervous
system consisting of cranial nerves arising
from the brain and spinal nerves arising from
the spinal cord. The brain thus allows us to
think and take actions based on that thinking.
As you will expect, this is accomplished
through a complex design, with different parts
of the brain responsible for integrating different
inputs and outputs. The brain has three such
major parts or regions, namely the fore-brain,
mid-brain and hind-brain.
The fore-brain is the main thinking part
of the brain. It has regions which receive
sensory impulses from various receptors.
Separate areas of the fore-brain are specialised
for hearing, smell, sight and so on. There are
separate areas of association where this sensory
information is interpreted by putting it together
with information from other receptors as well
as with information that is already stored in the
brain. Based on all this, a decision is made
about how to respond and the information is
passed on to the motor areas which control the
movement of voluntary muscles, for example,
our leg muscles. However, certain sensations
are distinct from seeing or hearing, for
example, how do we know that we have eaten
enough? The sensation of feeling full is because
of a centre associated with hunger, which is in a
separate part of the fore-brain.
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
46 47
Of course, reex arcs have evolved in
animals because the thinking process of the
brain is not fast enough. In fact many animals
have very little or none of the complex neuron
network needed for thinking. So it is quite
likely that reex arcs have evolved as efcient
ways of functioning in the absence of true
thought processes. However, even after
complex neuron networks have come into
existence, reex arcs continue to be more
efcient for quick responses.
Can you now trace the sequence of events
which occur when a bright light is focussed on
your eyes?
6.1.2 Human Brain
Is reex action the only function of the
spinal cord? Obviously not, since we know that
we are thinking beings. Spinal cord is made up
of nerves which supply information to think
about. Thinking involves more complex
mechanisms Pand neural connections. These
are concentrated in the brain, which is the main
coordinating centre of the body. The brain and
spinal cord constitute the central nervous
system (Fig. 6.3). They receive information
from all parts of the body and integrate it.
We also think about our actions. Writing,
talking, moving a chair, clapping at the end of a
programme are examples of voluntary actions
which are based on deciding what to do next.
So, the brain also has to send messages to
muscles. This is the second way in which the
nervous system communicates with the
Figure 6.2 Reex arc
muscles. The communication between the
central nervous system and the other parts of
the body is facilitated by the peripheral nervous
system consisting of cranial nerves arising
from the brain and spinal nerves arising from
the spinal cord. The brain thus allows us to
think and take actions based on that thinking.
As you will expect, this is accomplished
through a complex design, with different parts
of the brain responsible for integrating different
inputs and outputs. The brain has three such
major parts or regions, namely the fore-brain,
mid-brain and hind-brain.
The fore-brain is the main thinking part
of the brain. It has regions which receive
sensory impulses from various receptors.
Separate areas of the fore-brain are specialised
for hearing, smell, sight and so on. There are
separate areas of association where this sensory
information is interpreted by putting it together
with information from other receptors as well
as with information that is already stored in the
brain. Based on all this, a decision is made
about how to respond and the information is
passed on to the motor areas which control the
movement of voluntary muscles, for example,
our leg muscles. However, certain sensations
are distinct from seeing or hearing, for
example, how do we know that we have eaten
enough? The sensation of feeling full is because
of a centre associated with hunger, which is in a
separate part of the fore-brain.
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|Ÿ³+6.2ç|Ÿr¿±sÁ#ás«#|Ÿ+

ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
48 49
Figure 6.3 Human brain
Study the labelled diagram of the human
brain. We have seen that the different parts have
specic functions. Can we nd out the function
of each part?
Let us look at the other use of the word
‘reex’ that we have talked about in the
introduction. Our mouth waters when we see
food we like without our meaning to. Our hearts
beat without our thinking about it. In fact, we
cannot control these actions easily by thinking
about them even if we wanted to. Do we have to
think about or remember to breathe or digest
food? So, in between the simple reex actions
like change in the size of the pupil, and the
thought out actions such as moving a chair,
there is another set of muscle movements over
which we do not have any thinking control.
Many of these involuntary actions are
controlled by the mid-brain and hind-brain. All
these involuntary actions including blood
pressure, salivation and vomiting are
controlled by the medulla in the hind-brain.
Think about activities like walking in a
straight line, riding a bicycle, picking up a
pencil. These are possible due to a part of the
hind-brain called the cerebellum. It is
responsible for precision of voluntary actions
and maintaining the posture and balance of the
body. Imagine what would happen if each of
these events failed to take place if we were not
thinking about it.
6.1.3 How are these Tissues protected?
A delicate organ like the brain, which is so
important for a variety of activities, needs to be
carefully protected. For this, the body is
designed so that the brain sits inside a bony box.
Inside the box, the brain is contained in a uid-
lled balloon which provides further shock
absorption. If you run your hand down the
middle of your back, you will feel a hard,
bumpy structure. This is the vertebral column
or backbone which protects the spinal cord.
6.1.4 How does the Nervous Tissue cause
Action?
So far, we have been talking about nervous
tissue, and how it collects information, sends it
around the body, processes information, makes
decisions based on information, and conveys
decisions to muscles for action. In other words,
when the action or movement is to be
performed, muscle tissue will do the nal job.
How do animal muscles move? When a nerve
impulse reaches the muscle, the muscle bre
must move. How does a muscle cell move? The
simplest notion of movement at the cellular
level is that muscle cells will move by changing
their shape so that they shorten. So the next
question is, how do muscle cells change their
shape? The answer must lie in the chemistry of
cellular components. Muscle cells have special
proteins that change both their shape and their
arrangement in the cell in response to nervous
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
48 49
Figure 6.3 Human brain
Study the labelled diagram of the human
brain. We have seen that the different parts have
specic functions. Can we nd out the function
of each part?
Let us look at the other use of the word
‘reex’ that we have talked about in the
introduction. Our mouth waters when we see
food we like without our meaning to. Our hearts
beat without our thinking about it. In fact, we
cannot control these actions easily by thinking
about them even if we wanted to. Do we have to
think about or remember to breathe or digest
food? So, in between the simple reex actions
like change in the size of the pupil, and the
thought out actions such as moving a chair,
there is another set of muscle movements over
which we do not have any thinking control.
Many of these involuntary actions are
controlled by the mid-brain and hind-brain. All
these involuntary actions including blood
pressure, salivation and vomiting are
controlled by the medulla in the hind-brain.
Think about activities like walking in a
straight line, riding a bicycle, picking up a
pencil. These are possible due to a part of the
hind-brain called the cerebellum. It is
responsible for precision of voluntary actions
and maintaining the posture and balance of the
body. Imagine what would happen if each of
these events failed to take place if we were not
thinking about it.
6.1.3 How are these Tissues protected?
A delicate organ like the brain, which is so
important for a variety of activities, needs to be
carefully protected. For this, the body is
designed so that the brain sits inside a bony box.
Inside the box, the brain is contained in a uid-
lled balloon which provides further shock
absorption. If you run your hand down the
middle of your back, you will feel a hard,
bumpy structure. This is the vertebral column
or backbone which protects the spinal cord.
6.1.4 How does the Nervous Tissue cause
Action?
So far, we have been talking about nervous
tissue, and how it collects information, sends it
around the body, processes information, makes
decisions based on information, and conveys
decisions to muscles for action. In other words,
when the action or movement is to be
performed, muscle tissue will do the nal job.
How do animal muscles move? When a nerve
impulse reaches the muscle, the muscle bre
must move. How does a muscle cell move? The
simplest notion of movement at the cellular
level is that muscle cells will move by changing
their shape so that they shorten. So the next
question is, how do muscle cells change their
shape? The answer must lie in the chemistry of
cellular components. Muscle cells have special
proteins that change both their shape and their
arrangement in the cell in response to nervous
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
50 51
electrical impulses. When this happens, new
arrangements of these proteins give the muscle
cells a shorter form. Remember when we talked
about muscle tissue in Class IX, there were
different kinds of muscles, such as voluntary
muscles and involuntary muscles. Based on
what we have discussed so far, what do you
think the differences between these would be?
1. What is the difference between a reex
action and walking?
2. What happens at the synapse between two
neurons?
3. Which part of the brain maintains posture
and equilibrium of the body?
4. How do we detect the smell of an agarbatti
(incense stick)?
5. What is the role of the brain in reex
action?
6.2 COORDINATION IN PLANTS
Animals have a nervous system for controlling
and coordinating the activities of the body. But
plants have neither a nervous system nor
muscles. So, how do they respond to stimuli?
When we touch the leaves of a chhui-mui (the
‘sensitive’ or ‘touch-me-not’ plant of the
Mimosa family), they begin to fold up and
droop. When a seed germinates, the root goes
down, the stem comes up into the air. What
happens? Firstly, the leaves of the sensitive
plant move very quickly in response to touch.
There is no growth involved in this movement.
On the other hand, the directional movement of
a seedling is caused by growth. If it is prevented
from growing, it will not show any movement.
So plants show two different types of
movement – one dependent on growth and the
other independent of growth.
6.2.1 Immediate Response to Stimulus
Let us think about the rst kind of movement,
such as that of the sensitive plant. Since no
growth is involved, the plant must actually
move its leaves in response to touch. But there
is no nervous tissue, nor any muscle tissue.
How does the plant detect the touch, and how
do the leaves move in response?
Figure 6.4 The sensitive plant
If we think about where exactly the plant is
touched, and what part of the plant actually
moves, it is apparent that movement happens at
a point different from the point of touch. So,
information that a touch has occurred must be
communicated. The plants also use electrical-
chemical means to convey this information
from cell to cell, but unlike in animals, there is
no specialised tissue in plants for the
conduction of information. Finally, again as in
animals, some cells must change shape in order
for movement to happen. Instead of the
specialised proteins found in animal muscle
cells, plant cells change shape by changing the
amount of water in them, resulting in swelling
or shrinking, and therefore in changing shapes
(Fig. 6.4).
6.2.2 Movement Due to Growth
Some plants like the pea plant climb up other
plants or fences by means of tendrils. These
tendrils are sensitive to touch. When they come
in contact with any support, the part of the
tendril in contact with the object does not grow
as rapidly as the part of the tendril away from
the object. This causes the tendril to circle
around the object and thus cling to it. More
commonly, plants respond to stimuli slowly by
growing in a particular direction. Because this
growth is directional, it appears as if the plant is
moving. Let us understand this type of
movement with the help of an example.
Figure 6.4 The sensitive plant
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
52 53
Activity 6.2
gFill a conical ask with water.
gCover the neck of the ask with a wire
mesh.
gKeep two or three freshly germinated
bean seeds on the wire mesh.
gTake a cardboard box which is open from
one side.
gKeep the ask in the box in such a
manner that the open side of the box
faces light coming from a window (Fig.
6.5).
gAfter two or three days, you will notice
that the shoots bend towards light and
roots away from light.
gNow turn the ask so that the shoots are
away from light and the roots towards
light. Leave it undisturbed in this
condition for a few days.
gHave the old parts of the shoot and root
changed direction?
gAre there differences in the direction of
the new growth?
gWhat can we conclude from this
activity?
Figure 6.5
Response of the plant to the direction of light
Figure 6.6 Plant showing geotropism
Environmental triggers such as light, or
gravity will change the directions that plant parts
grow in. These directional, or tropic, movements
can be either towards the stimulus, or away from
it. So, in two different kinds of phototropic
movement, shoots respond by bending towards
light while roots respond by bending away from
it. How does this help the plant?
Plants show tropism in response to other
stimuli as well. The roots of a plant always
grow downwards while the shoots usually grow
upwards and away from the earth. This upward
and downward growth of shoots and roots,
respectively, in response to the pull of earth or
gravity is, obviously, geotropism (Fig. 6.6). If
‘hydro’ means water and ‘chemo’ refers to
chemicals, what would ‘hydrotropism’ and
‘chemotropism’ mean? Can we think of
examples of these kinds of directional growth
movements? One example of chemotropism is
the growth of pollen tubes towards ovules,
about which we will learn more when we
examine the reproductive processes of living
organisms.
Let us now once again think about how
information is communicated in the bodies of
multicellular organisms. The movement of the
sensitive plant in response to touch is very
quick. The movement of sunowers in
response to day or night, on the other hand, is
quite slow. Growth-related movement of plants
will be even slower.
Even in animal bodies, there are
carefully controlled directions to growth. Our
arms and ngers grow in certain directions, not
haphazardly. So controlled movements can be
either slow or fast. If fast responses to stimuli
are to be made, information transfer must
happen very quickly. For this, the medium of
transmission must be able to move rapidly.
Electrical impulses are an excellent
means for this. But there are limitations to the
use of electrical impulses. Firstly, they will
reach only those cells that are connected by
nervous tissue, not each and every cell in the
animal body. Secondly, once an electrical
impulse is generated in a cell and transmitted,
the cell will take some time to reset its
mechanisms before it can generate and transmit
a new impulse. In other words, cells cannot
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
54 55
continually create and transmit electrical
impulses. It is thus no wonder that most
multicellular organisms use another means of
communication between cells, namely,
chemical communication.
If, instead of generating an electrical
impulse, stimulated cells release a chemical
compound, this compound would diffuse all
around the original cell. If other cells around
have the means to detect this compound using
special molecules on their surfaces, then they
would be able to recognise information, and
even transmit it. This will be slower, of course,
but it can potentially reach all cells of the body,
regardless of nervous connections, and it can be
done steadily and persistently. These
compounds, or hormones used by multicellular
organisms for control and coordination show a
great deal of diversity, as we would expect.
Different plant hormones help to coordinate
growth, development and responses to the
environment. They are synthesised at places
away from where they act and simply diffuse to
the area of action.
Let us take an example that we have
worked with earlier [Activity 6.2]. When
growing plants detect light, a hormone called
auxin, synthesised at the shoot tip, helps the
cells to grow longer. When light is coming from
one side of the plant, auxin diffuses towards the
shady side of the shoot. This concentration of
auxin stimulates the cells to grow longer on the
side of the shoot which is away from light.
Thus, the plant appears to bend towards light.
Another example of plant hormones are
gibberellins which, like auxins, help in the
growth of the stem. Cytokinins promote cell
division, and it is natural then that they are
present in greater concentration in areas of
rapid cell division, such as in fruits and seeds.
These are examples of plant hormones that help
in promoting growth. But plants also need
signals to stop growing. Abscisic acid is one
example of a hormone which inhibits growth.
Its effects include wilting of leaves.
1. What are plant hormones?
2. How is the movement of leaves of the
sensitive plant different from the
movement of a shoot towards light?
3. Give an example of a plant hormone that
promotes growth.
4. How do auxins promote the growth of a
tendril around a support?
5. Design an experiment to demonstrate
hydrotropism.
6.3 HORMONES IN ANIMALS
How are such chemical, or hormonal, means of
information transmission used in animals?
What do some animals, for instance squirrels,
experience when they are in a scary situation?
Their bodies have to prepare for either ghting
or running away. Both are very complicated
activities that will use a great deal of energy in
controlled ways. Many different tissue types
will be used and their activities integrated
together in these actions. However, the two
alternate activities, ghting or running, are also
quite different! So here is a situation in which
some common preparations can be usefully
made in the body. These preparations should
ideally make it easier to do either activity in the
near future. How would this be achieved?
If the body design in the squirrel relied
only on electrical impulses via nerve cells, the
range of tissues instructed to prepare for the
coming activity would be limited. On the other
hand, if a chemical signal were to be sent as
well, it would reach all cells of the body and
provide the wide-ranging changes needed. This
is done in many animals, including human
beings, using a hormone called adrenaline that
is secreted from the adrenal glands. Look at Fig.
6.7 to locate these glands.
Adrenaline is secreted directly into the
blood and carried to different parts of the body.
The target organs or the specic tissues on which
it acts include the heart. As a result, the heart
beats faster, resulting in supply of more oxygen
to our muscles. The blood to the digestive system
and skin is reduced due to contraction of muscles
around small arteries in these organs. This diverts
the blood to our skeletal muscles. The breathing
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
56 57
rate also increases because of the contractions of
the diaphragm and the rib muscles. All these
responses together enable the animal body to be
ready to deal with the situation. Such animal
hormones are part of the endocrine system which
constitutes a second way of control and
coordination in our body.
Activity 6.3
gLook at Fig. 6.7.
gIdentify the endocrine glands mentioned
in the gure.
gSome of these glands have been listed in
Table 6.1 and discussed in the text.
Consult books in the library and discuss
with your teachers to nd out about other
glands.
Remember that plants have hormones
that control their directional growth. What
functions do animal hormones perform? On the
face of it, we cannot imagine their role in
directional growth. We have never seen an
animal growing more in one direction or the
other, depending on light or gravity! But if we
think about it a bit more, it will become evident
that, even in animal bodies, growth happens in
carefully controlled places. Plants will grow
leaves in many places on the plant body, for
example. But we do not grow ngers on our
faces. The design of the body is carefully
maintained even during the growth of children.
Figure 6.7 Endocrine glands in human beings (a) male, (b) female
(a) (b)
Do You Know?
Hypothalamus plays an important role in the
release of many hormones. For example,
when the level of growth hormone is low, the
hypothalamus releases growth hormone
releasing factor which stimulates the
pituitary gland to release growth hormone.
Let us examine some examples to
understand how hormones help in coordinated
growth. We have all seen salt packets which say
‘iodised salt’ or ‘enriched with iodine’. Why is
it important for us to have iodised salt in our
diet? Iodine is necessar for the thyroid gland to
make thyroxin hormone. Thyroxin regulates
carbohydrate, protein and fat metabolism in the
body so as to provide the best balance for
growth. Iodine is essential for the synthesis of
thyroxin. In case iodine is decient in our diet,
there is a possibility that we might suffer from
goitre. One of the symptoms in this disease is a
swollen neck. Can you correlate this with the
position of the thyroid gland in Fig. 6.7?
Sometimes we come across people who
are either very short (dwarfs) or extremely tall
(giants). Have you ever wondered how this
happens? Growth hormone is one of the
hormones secreted by the pituitary. As its name
indicates, growth hormone regulates growth
and development of the body. If there is a
deciency of this hormone in childhood, it
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ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
58 59
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leads to dwarsm.
You must have noticed many dramatic
changes in your appearance as well as that of
your friends as you approached 10–12 years of
age. These changes associated with puberty are
because of the secretion of testosterone in
males and oestrogen in females.
Do you know anyone in your family or
friends who has been advised by the doctor to
take less sugar in their diet because they are
suffering from diabetes? As a treatment, they
might be taking injections of insulin. This is a
hormone which is produced by the pancreas
and helps in regulating blood sugar levels. If it
is not secreted in proper amounts, the sugar
level in the blood rises causing many harmful
effects.
If it is so important that hormones
should be secreted in precise quantities, we
1. How does chemical coordination take
place in animals?
2. Why is the use of iodised salt advisable?
3. How does our body respond when
adrenaline is secreted into the blood?
4. Why are some patients of diabetes treated
by giving injections of insulin?
need a mechanism through which this is done.
The timing and amount of hormone released
are regulated by feedback mechanisms. For
example, if the sugar levels in blood rise, they
are detected by the cells of the pancreas which
respond by producing more insulin. As the
blood sugar level falls, insulin secretion is
reduced.
gHormones are secreted by endocrine glands and have specic functions. Complete Table 6.1
based on the hormone, the endocrine gland or the functions provided.
Table 6.1 : Some important hormones and their functions
S.No. Hormone Endocrine Gland Functions
1. Growth hormone Pituitary gland Stimulates growth in all organs
2. Thyroid gland Regulates metabolism for body growth
3. Insulin Regulates blood sugar level
4. Testosterone Testes
5. Ovaries Development of female sex organs,
regulates menstrual cycle, etc.
6. Adrenaline Adrenal gland
7. Releasing Stimulates pituitary gland to release
hormones hormones
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What you have learnt
gControl and coordination are the functions of the nervous system and hormones in our bodies.
gThe responses of the nervous system can be classied as reex action, voluntary action or
involuntary action.
gThe nervous system uses electrical impulses to transmit messages.
gThe nervous system gets information from our sense organs and acts through our muscles.
gChemical coordination is seen in both plants and animals.
gHormones produced in one part of an organism move to another part to achieve the desired
effect.
gA feedback mechanism regulates the action of the hormones.
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Thyroxine
Progesterone
Estrogen

ANDHRA PRADESH | Biology : Control and Coordination €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :“jáT+çÔáDeT]jáTTdŸeTqÇjáT+
60 61
EXERCISES
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
4. What is the function of receptors in our body? Think of situations where receptors do not
work properly. What problems are likely to arise?
5. Draw the structure of a neuron and explain its function.
6. How does phototropism occur in plants?
7. Which signals will get disrupted in case of a spinal cord injury?
8. How does chemical coordination occur in plants?
9. What is the need for a system of control and coordination in an organism?
10. How are involuntary actions and reex actions different from each other?
11. Compare and contrast nervous and hormonal mechanisms for control and coordination
in animals.
12. What is the difference between the manner in which movement takes place in a sensitive
plant and the movement in our legs?
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
64
65
B
efore we discuss the mechanisms by
which organisms reproduce, let us ask a
more basic question – why do organisms
reproduce? After all, reproduction is not
necessary to maintain the life of an individual
organism, unlike the essential life processes
such as nutrition, respiration, or excretion. On
the other hand, if an individual organism is
going to create more individuals, a lot of its
energy will be spent in the process. So why
should an individual organism waste energy on
a process it does not need to stay alive? It would
be interesting to discuss the possible answers in
the classroom!
Whatever the answer to this question, it
is obvious that we notice organisms because
they reproduce. If there were to be only one,
non-reproducing member of a particular kind, it
is doubtful that we would have noticed its
existence. It is the large numbers of organisms
belonging to a single species that bring them to
our notice. How do we know that two different
individual organisms belong to the same
species? Usually, we say this because they look
similar to each other. Thus, reproducing
organisms create new individuals that look
very much like themselves.
7.1 DO ORGANISMS CREATE EXACT
COPIES OF THEMSELVES?
Organisms look similar because their body
designs are similar. If body designs are to be
similar, the blueprints for these designs should
be similar. Thus, reproduction at its most basic
level will involve making copies of the
blueprints of body design. In Class IX, we
learnt that the chromosomes in the nucleus of a
cell contain information for inheritance of
features from parents to next generation in the
form of DNA (Deoxyribo Nucleic Acid)
molecules. The DNA in the cell nucleus is the
information source for making proteins. If the
information is changed, different proteins will
be made. Different proteins will eventually lead
to altered body designs.
Therefore, a basic event in reproduction
is the creation of a DNA copy. Cells use
chemical reactions to build copies of their
DNA. This creates two copies of the DNA in a
reproducing cell, and they will need to be
separated from each other. However, keeping
one copy of DNA in the original cell and simply
pushing the other one out would not work,
because the copy pushed out would not have
any organised cellular structure for maintaining
life processes. Therefore, DNA copying is
accompanied by the creation of an additional
cellular apparatus, and then the DNA copies
separate, each with its own cellular apparatus.
Effectively, a cell divides to give rise to two
cells.
These two cells are of course similar, but
are they likely to be absolutely identical? The
answer to this question will depend on how
accurately the copying reactions involved
occur. No bio-chemical reaction is absolutely
reliable. Therefore, it is only to be expected that
the process of copying the DNA will have some
variations each time. As a result, the DNA
copies generated will be similar, but may not be
identical to the original. Some of these
variations might be so drastic that the new DNA
copy cannot work with the cellular apparatus it
inherits. Such a newborn cell will simply die.
On the other hand, there could still be many
other variations in the DNA copies that would
not lead to such a drastic outcome. Thus, the
surviving cells are similar to, but subtly
different from each other. This inbuilt tendency
for variation during reproduction is the basis
for evolution, as we will discuss in the next
chapter.
7.1.1 The Importance of Variation
Populations of organisms ll well-
dened places, or niches, in the ecosystem,
using their ability to reproduce. The
consistency of DNA copying during
reproduction is important for the maintenance
of body design features that allow the organism
to use that particular niche. Reproduction is
therefore linked to the stability of populations
of species.
However, niches can change because of
reasons beyond the control of the organisms.
Temperatures on earth can go up or down,
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
66
67
water levels can vary, or there could be
meteorite hits, to think of a few examples. If a
population of reproducing organisms were
suited to a particular niche and if the niche were
drastically altered, the population could be
wiped out. However, if some variations were to
be present in a few individuals in these
populations, there would be some chance for
them to survive. Thus, if there were a
population of bacteria living in temperate
waters, and if the water temperature were to be
increased by global warming, most of these
bacteria would die, but the few variants
resistant to heat would survive and grow
further. Variation is thus useful for the survival
of species over time.
1. What is the importance of DNA copying in
reproduction?
2. Why is variation benecial to the species
but not necessarily for the individual?
7.2 MODES OF REPRODUCTION USED
BY SINGLE ORGANISMS
Activity 7.1
Activity 7.3
Activity 7.2
gDissolve about 10 gm of sugar in 100 mL
of water.
gTake 20 mL of this solution in a test tube
and add a pinch of yeast granules to it.
gPut a cotton plug on the mouth of the test
tube and keep it in a warm place.
gAfter 1 or 2 hours, put a small drop of
yeast culture from the test tube on a slide
and cover it with a coverslip.
gObserve the slide under a microscope.
gObserve a permanent slide of Amoeba
under a microscope.
gSimilarly observe another permanent
slide of Amoeba showing binary ssion.
gNow, compare the observations of both
the slides.
gWet a slice of bread, and keep it in a cool,
moist and dark place.
gObserve the surface of the slice with a
magnifying glass.
gRecord your observations for a week.
Compare and contrast the ways in which
yeast grows in the rst case, and how mould
grows in the second.
Having discussed the context in which
reproductive processes work, let us now
examine how different organisms actually
reproduce. The modes by which various
organisms reproduce depend on the body
design of the organisms.
7.2.1 Fission
For unicellular organisms, cell division, or
ssion, leads to the creation of new individuals.
Many different patterns of ssion have been
observed. Many bacteria and protozoa simply
split into two equal halves during cell division.
In organisms such as Amoeba, the splitting of
the two cells during division can take place in
any plane.
However, some unicellular organisms show
somewhat more organisation of their bodies,
such as is seen in Leishmania (which cause
kala-azar), which have a whip-like structure at
one end of the cell. In such organisms, binary
ssion occurs in a denite orientation in
relation to these structures. Other single-celled
organisms, such as the malarial parasite,
Plasmodium, divide into many daughter cells
simultaneously by multiple ssion.
Figure 7.1
(a) Binary ssion in Amoeba
Figure 7.1 (b) Binary ssion in Leishmania
(a) (b) (c) (d) (e) (f)
(a) (b) (c) (d) (e) (f)
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
68
69
Figure 7.2 Multiple ssion in Plasmodium
7.2.2 Fragmentation
gCollect water from a lake or pond that
appears dark green and contains
lamentous structures.
gPut one or two laments on a slide.
gPut a drop of glycerine on these laments
and cover it with a cover slip.
gObserve the slide under a microscope.
gCan you identify different tissues in the
Spirogyra laments?
Activity 7.4
In multi-cellular organisms with
relatively simple body organisation, simple
reproductive methods can still work.
Spirogyra, for example, simply breaks up into
smaller pieces upon maturation. These pieces
or fragments grow into new individuals. Can
we work out the reason for this, based on what
we saw in Activity 7.4?
This is not true for all multi-cellular
organisms. They cannot simply divide cell-by-
cell. The reason is that many multi-cellular
organisms, as we have seen, are not simply a
random collection of cells. Specialised cells are
organised as tissues, and tissues are organised
into organs, which then have to be placed at
denite positions in the body. In such a
carefully organised situation, cell-by-cell
division would be impractical. Multi-cellular
organisms, therefore, need to use more
complex ways of reproduction.
A basic strategy used in multi-cellular
organisms is that different cell types perform
different specialised functions. Following this
general pattern, reproduction in such organisms
is also the function of a specic cell type. How
is reproduction to be achieved from a single cell
type, if the organism itself consists of many cell
types? The answer is that there must be a single
cell type in the organism that is capable of
growing, proliferating and making other cell
types under the right circumstances.
7.2.3 Regeneration
Many fully differentiated organisms have the
ability to give rise to new individual organisms
from their body parts. That is, if the individual
is somehow cut or broken up into many pieces,
many of these pieces grow into separate
individuals. For example, simple animals like
Hydra and Planaria can be cut into any number
of pieces and each piece grows into a complete
organism. This is known as regeneration (see
Fig.7.3). Regeneration is carried out by
specialised cells. These cells proliferate and
make large numbers of cells. From this mass of
cells, different cells undergo changes to
become various cell types and tissues. These
changes take place in an organised sequence
referred to as development. However,
regeneration is not the same as reproduction,
since most organisms would not normally
depend on being cut up to be able to reproduce.
Figure 7.3
Regeneration in Planaria
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Yeast, on the other hand, can put out small buds
that separate and grow further, as we saw in
Activity 7.1.
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7.2.4 Budding
Organisms such as Hydra use
regenerative cells for reproduction in the
process of budding. In Hydra, a bud develops
as an outgrowth due to repeated cell division at
one specic site (Fig. 7.4). These buds develop
into tiny individuals and when fully mature,
detach from the parent body and become new
independent individuals.
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
70
71
Figure 7.4 Budding in Hydra
7.2.5 Vegetative Propagation
There are many plants in which parts like the
root, stem and leaves develop into new plants
under appropriate conditions. Unlike in most
animals, plants can indeed use such a mode for
reproduction. This property of vegetative
propagation is used in methods such as layering
or grafting to grow many plants like sugarcane,
roses, or grapes for agricultural purposes.
Plants raised by vegetative propagation can
bear owers and fruits earlier than those
produced from seeds. Such methods also make
possible the propagation of plants such as
banana, orange, rose and jasmine that have lost
the capacity to produce seeds. Another
advantage of vegetative propagation is that all
plants produced are genetically similar enough
to the parent plant to have all its characteristics.
Similarly buds produced in the notches
along the leaf margin of Bryophyllum fall on the
soil and develop into new plants (Fig. 7.5).
gTake a potato and observe its surface.
Can notches be seen?
gCut the potato into small pieces such that
some pieces contain a notch or bud and
some do not.
gSpread some cotton on a tray and wet it.
Place the potato pieces on this cotton.
Note where the pieces with the buds are
placed.
Activity 7.5
Figure 7.5
Leaf of Bryophyllum with buds
gSelect a money-plant.
gCut some pieces such that they contain at
least one leaf.
gCut out some other portions between two
leaves.
gDip one end of all the pieces in water and
observe over the next few days.
gWhich ones grow and give rise to fresh
leaves?
gWhat can you conclude from your
observations?
Activity 7.6
gObserve changes taking place in these
potato pieces over the next few days.
Make sure that the cotton is kept
moistened.
gWhich are the potato pieces that give rise
to fresh green shoots and roots?
Tissue culture
In tissue culture, new plants are grown by removing tissue or separating cells from the growing tip
of a plant. The cells are then placed in an articial medium where they divide rapidly to form a
small group of cells or callus. The callus is transferred to another medium containing hormones
for growth and differentiation. The plantlets are then placed in the soil so that they can grow into
mature plants. Using tissue culture, many plants can be grown from one parent in disease-free
conditions. This technique is commonly used for ornamental plants.
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
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Figure 7.6
Spore formation in Rhizopus
7.2.6 Spore Formation
Even in many simple multi-cellular organisms,
specic reproductive parts can be identied.
The thread-like structures that developed on the
bread in Activity 7.2 above are the hyphae of
the bread mould (Rhizopus). They are not
reproductive parts. On the other hand, the tiny
blob-on-a-stick structures are involved in
reproduction. The blobs are sporangia, which
contain cells, or spores, that can eventually
develop into new Rhizopus individuals (Fig.
7.6). The spores are covered by thick walls that
protect them until they come into contact with
another moist surface and can begin to grow.
All the modes of reproduction that we have
discussed so far allow new generations to be
created from a single individual. This is known
as asexual reproduction.
1. How does binary ssion differ from
multiple ssion?
2. How will an organism be beneted if it
reproduces through spores?
3. Can you think of reasons why more
complex organisms cannot give rise to
new individuals through regeneration?
4. Why is vegetative propagation practised
for growing some types of plants?
5. Why is DNA copying an essential part of
the process of reproduction?
7.3 SEXUAL REPRODUCTION
We are also familiar with modes of
reproduction that depend on the involvement of
two individuals before a new generation can be
created. Bulls alone cannot produce new
calves, nor can hens alone produce new chicks.
In such cases, both sexes, males and females,
are needed to produce new generations. What is
the signicance of this sexual mode of
reproduction? Are there any limitations of the
asexual mode of reproduction, which we have
been discussing above?
7.3.1 Why the Sexual Mode of Reproduction?
The creation of two new cells from one
involves copying of the DNA as well as of the
cellular apparatus. The DNA copying
mechanism, as we have noted, cannot be
absolutely accurate, and the resultant errors are
a source of variations in populations of
organisms. Every individual organism cannot
be protected by variations, but in a population,
variations are useful for ensuring the survival
of the species. It would therefore make sense if
organisms came up with reproductive modes
that allowed more and more variation to be
generated.
While DNA-copying mechanisms are not
absolutely accurate, they are precise enough to
make the generation of variation a fairly slow
process. If the DNA copying mechanisms were
to be less accurate, many of the resultant DNA
copies would not be able to work with the
cellular apparatus, and would die. So how can
the process of making variants be speeded up?
Each new variation is made in a DNA copy that
already has variations accumulated from
previous generations. Thus, two different
individuals in a population would have quite
different patterns of accumulated variations.
Since all of these variations are in living
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ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
74
75
individuals, it is assured that they do not have
any really bad effects. Combining variations
from two or more individuals would thus create
new combinations of variants. Each
combination would be novel, since it would
involve two different individuals. The sexual
mode of reproduction incorporates such a
process of combining DNA from two different
individuals during reproduction.
But this creates a major difculty. If each
new generation is to be the combination of the
DNA copies from two pre-existing individuals,
then each new generation will end up having
twice the amount of DNA that the previous
generation had. This is likely to mess up the
control of the cellular apparatus by the DNA.
How many ways can we think of for solving
this difculty?
We have seen earlier that as organisms
become more complex, the specialisation of
tissue increases. One solution that many multi-
cellular organisms have found for the problem
mentioned above is to have special lineages of
cells in specialised organs in which only half
the number of chromosomes and half the
amount of DNA as compared to the non-
reproductive body cells. This is achieved by a
process of cell division called meiosis. Thus,
when these germ-cells from two individuals
combine during sexual reproduction to form a
new individual, it results in re-establishment of
the number of chromosomes and the DNA
content in the new generation.
If the zygote is to grow and develop into an
organism which has highly specialised tissues
and organs, then it has to have sufcient stores
of energy for doing this. In very simple
organisms, it is seen that the two germ-cells are
not very different from one another, or may
even be similar. But as the body designs
become more complex, the germ-cells also
specialise. One germ-cell is large and contains
the food-stores while the other is smaller and
likely to be motile. Conventionally, the motile
germ-cell is called the male gamete and the
germ-cell containing the stored food is called
the female gamete. We shall see in the next few
sections how the need to create these two
different types of gametes give rise to
differences in the male and female reproductive
organs and, in some cases, differences in the
bodies of the male and female organisms.
7.3.2 Sexual Reproduction in Flowering
Plants
The reproductive parts of angiosperms are
located in the ower. You have already studied
the different parts of a ower – sepals, petals,
stamens and pistil. Stamens and pistil are the
reproductive parts of a ower which contain the
germ-cells. What possible functions could the
petals and sepals serve?
The ower may be unisexual (papaya,
watermelon) when it contains either stamens or
pistil or bisexual (Hibiscus, mustard) when it
contains both stamens and pistil. Stamen is the
male reproductive part and it produces pollen
grains that are yellowish in colour. You must
have seen this yellowish powder that often
sticks to our hands if we touch the stamen of a
ower. Pistil is present in the centre of a ower
and is the female reproductive part. It is made
of three parts.
Figure 7.7
Longitudinal section of ower
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|ŸÚwŸÎ+“\TeÚ¿ÃÔá

ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
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77
The swollen bottom part is the ovary, middle
elongated part is the style and the terminal part
which may be sticky is the stigma. The ovary
contains ovules and each ovule has an egg cell.
The male germ-cell produced by pollen grain
fuses with the female gamete present in the
ovule. This fusion of the germ-cells or
fertilisation gives us the zygote which is
capable of growing into a new plant.
Thus the pollen needs to be transferred
from the stamen to the stigma. If this transfer of
pollen occurs in the same ower, it is referred to
as self-pollination. On the other hand, if the
pollen is transferred from one ower to another,
it is known as cross-pollination. This transfer of
pollen from one ower to another is achieved
by agents like wind, water or animals.
After the pollen lands on a suitable
stigma, it has to reach the female germ-cells
which are in the ovary. For this, a tube grows
out of the pollen grain and travels through the
style to reach the ovary.
After fertilisation, the zygote divides
several times to form an embryo within the
ovule. The ovule develops a tough coat and is
gradually converted into a seed. The ovary
grows rapidly and ripens to form a fruit.
Meanwhile, the petals, sepals, stamens, style
and stigma may shrivel and fall off. Have you
ever observed any ower part still persisting in
the fruit? Try and work out the advantages of
seed-formation for the plant. The seed contains
the future plant or embryo which develops into
a seedling under appropriate conditions. This
process is known as germination.
Activity 7.7
gSoak a few seeds of Bengal gram (chana)
and keep them overnight.
gDrain the excess water and cover the
seeds with a wet cloth and leave them for a
day. Make sure that the seeds do not
become dry.
gCut open the seeds carefully and observe
the different parts.
gCompare your observations with the Fig.
7.9 and see if you can identify all the parts.
7.3.3 Reproduction in Human Beings
So far, we have been discussing the variety of
modes that different species use for
reproduction. Let us now look at the species
that we are most interested in, namely, humans.
Humans use a sexual mode of reproduction.
How does this process work?
Let us begin at an apparently unrelated
point. All of us know that our bodies change as
we become older. You have learnt changes that
take place in your body earlier in Class VIII
also. We notice that our height has increased
continuously from early age till now. We
acquire teeth, we even lose the old, so-called
milk teeth and acquire new ones.
Figure 7.8
Germination of pollen on stigma
Figure 7.9 Germination
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;È<ŠÞø+

ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
78
79
All of these are changes that can be grouped
under the general process of growth, in which
the body becomes larger. But in early teenage
years, a whole new set of changes occurs that
cannot be explained simply as body
enlargement. Instead, the appearance of the
body changes. Proportions change, new
features appear, and so do new sensations.
Some of these changes are common to both
boys and girls. We begin to notice thick hair
growing in new parts of the body such as armpits
and the genital area between the thighs, which
can also become darker in colour. Thinner hair
can also appear on legs and arms, as well as on
the face. The skin frequently becomes oily and
we might begin to develop pimples. We begin to
be conscious and aware of both our own bodies
and those of others in new ways.
On the other hand, there are also changes
taking place that are different between boys and
girls. In girls, breast size begins to increase,
with darkening of the skin of the nipples at the
tips of the breasts. Also, girls begin to
menstruate at around this time. Boys begin to
have new thick hair growth on the face and their
voices begin to crack. Further, the penis
occasionally begins to become enlarged and
erect, either in daydreams or at night.
All of these changes take place slowly,
over a period of months and years. They do not
happen all at the same time in one person, nor
do they happen at an exact age. In some people,
they happen early and quickly, while in others,
they can happen slowly. Also, each change does
not become complete quickly either. So, for
example, thick hair on the face in boys appears
as a few scattered hairs rst, and only slowly
does the growth begin to become uniform.
Even so, all these changes show differences
between people. Just as we have differently
shaped noses or ngers, so also we have
different patterns of hair growth, or size and
shape of breast or penis. All of these changes
are aspects of the sexual maturation of the body.
Why does the body show sexual
maturation at this age? We have talked about
the need for specialised cell types in multi-
cellular bodies to carry out specialised
functions. The creation of germ-cells to
participate in sexual reproduction is another
specialised function, and we have seen that
plants develop special cell and tissue types to
create them. Human beings also develop
special tissues for this purpose. However, while
the body of the individual organism is growing
to its adult size, the resources of the body are
mainly directed at achieving this growth. While
that is happening, the maturation of the
reproductive tissue is not likely to be a major
priority. Thus, as the rate of general body
growth begins to slow down, reproductive
tissues begin to mature. This period during
adolescence is called puberty.
So how do all the changes that we have
talked about link to the reproductive process?
We must remember that the sexual mode of
reproduction means that germ-cells from two
individuals have to join together. This can
happen by the external release of germ-cells
from the bodies of individuals, as happens in
owering plants. Or it can happen by two
individuals joining their bodies together for
internal transfer of germ-cells for fusion, as
happens in many animals. If animals are to
participate in this process of mating, their state
of sexual maturity must be identiable by other
individuals. Many changes during puberty,
such as new hair-growth patterns, are signals
that sexual maturation is taking place.
On the other hand, the actual transfer of
germ-cells between two people needs special
organs for the sexual act, such as the penis when
it is capable of becoming erect. In mammals such
as humans, the baby is carried in the mother’s
body for a long period, and will be breast-fed
later. The female reproductive organs and breasts
will need to mature to accommodate these
possibilities. Let us look at the systems involved
in the process of sexual reproduction.
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80
81
7.3.3 (a) Male Reproductive System
The male reproductive system (Fig. 7.10)
consists of portions which produce the germ-
cells and other portions that deliver the germ-
cells to the site of fertilisation.
The formation of germ-cells or sperms
takes place in the testes. These are located
outside the abdominal cavity in scrotum because
sperm formation requires a lower temperature
than the normal body temperature. We have
discussed the role of the testes in the secretion of
the hormone, testosterone, in the previous
chapter. In addition to regulating the formation of
sperms, testosterone brings about changes in
appearance seen in boys at the time of puberty.
The sperms formed are delivered through
the vas deferens which unites with a tube coming
from the urinary bladder. The urethra thus forms
a common passage for both the sperms and urine.
Along the path of the vas deferens, glands like the
prostate and the seminal vesicles add their
secretions so that the sperms are now in a uid
which makes their transport easier and this uid
also provides nutrition. The sperms are tiny
bodies that consist of mainly genetic material
and a long tail that helps them to move towards
the female germ-cell.
7.3.3 (b) Female Reproductive System
The female germ-cells or eggs are made in the
ovaries. They are also responsible for the
production of some hormones. Look at Fig.
7.11 and identify the various organs in the
female reproductive system.
When a girl is born, the ovaries already
contain thousands of immature eggs. On
reaching puberty, some of these start maturing.
One egg is produced every month by one of the
ovaries. The egg is carried from the ovary to the
womb through a thin oviduct or fallopian tube.
The two oviducts unite into an elastic bag-like
structure known as the uterus. The uterus opens
into the vagina through the cervix.
The sperms enter through the vaginal
passage during sexual intercourse. They travel
upwards and reach the oviduct where they may
encounter the egg. The fertilised egg (zygote)
starts dividing and form a ball of cells or
embryo. The embryo is implanted in the lining
of the uterus where they continue to grow and
develop organs to become foetus. We have seen
in earlier sections that the mother’s body is
designed to undertake the development of the
child. Hence the uterus prepares itself every
month to receive and nurture the growing
embryo. The lining thickens and is richly
supplied with blood to nourish the growing
embryo.
The embryo gets nutrition from the
mother’s blood with the help of a special tissue
called placenta. This is a disc which is
embedded in the uterine wall. It contains villi
on the embryo’s side of the tissue. On the
mother’s side are blood spaces, which surround
Figure 7.10
Human–male reproductive system
Figure 7.11 Human–female reproductive system
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the villi. This provides a large surface area for
glucose and oxygen to pass from the mother to
the embryo. The developing embryo will also
generate waste substances which can be
removed by transferring them into the mother’s
blood through the placenta. The development
of the child inside the mother’s body takes
approximately nine months. The child is born
as a result of rhythmic contractions of the
muscles in the uterus.
7.3.3 (c) What happens when the Egg is not
Fertilised?
If the egg is not fertilised, it lives for about one
day. Since the ovary releases one egg every
month, the uterus also prepares itself every
month to receive a fertilised egg. Thus its lining
becomes thick and spongy. This would be
required for nourishing the embryo if
fertilisation had taken place. Now, however,
this lining is not needed any longer. So, the
lining slowly breaks and comes out through the
vagina as blood and mucous. This cycle takes
place roughly every month and is known as
menstruation. It usually lasts for about two to
eight days.
7.3.3 (d) Reproductive Health
As we have seen, the process of sexual
maturation is gradual, and takes place while
general body growth is still going on.
Therefore, some degree of sexual maturation
does not necessarily mean that the body or the
mind is ready for sexual acts or for having and
bringing up children. How do we decide if the
body or the mind is ready for this major
responsibility? All of us are under many
different kinds of pressures about these issues.
There can be pressure from our friends for
participating in many activities, whether we
really want to or not. There can be pressure
from families to get married and start having
children. There can be pressure from
government agencies to avoid having children.
In this situation, making choices can become
very difcult.
We must also consider the possible health
consequences of having sex. We have
discussed in Class IX that diseases can be
transmitted from person to person in a variety
of ways. Since the sexual act is a very intimate
connection of bodies, it is not surprising that
many diseases can be sexually transmitted.
These include bacterial infections such as
gonorrhoea and syphilis, and viral infections
such as warts and HIV-AIDS. Is it possible to
prevent the transmission of such diseases
during the sexual act? Using a covering, called
a condom, for the penis during sex helps to
prevent transmission of many of these
infections to some extent.
The sexual act always has the potential to
lead to pregnancy. Pregnancy will make major
demands on the body and the mind of the
woman, and if she is not ready for it, her health
will be adversely affected. Therefore, many
ways have been devised to avoid pregnancy.
These contraceptive methods fall in a number
of categories. One category is the creation of a
mechanical barrier so that sperm does not reach
the egg. Condoms on the penis or similar
coverings worn in the vagina can serve this
purpose. Another category of contraceptives
acts by changing the hormonal balance of the
body so that eggs are not released and
fertilisation cannot occur. These drugs
commonly need to be taken orally as pills.
However, since they change hormonal
balances, they can cause side-effects too. Other
contraceptive devices such as the loop or the
copper-T are placed in the uterus to prevent
pregnancy. Again, they can cause side effects
due to irritation of the uterus. If the vas deferens
in the male is blocked, sperm transfer will be
prevented. If the fallopian tube in the female is
blocked, the egg will not be able to reach the
uterus. In both cases fertilisation will not take
place. Surgical methods can be used to create
such blocks. While surgical methods are safe in
the long run, surgery itself can cause infections

ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
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85
1. How is the process of pollination different
from fertilisation?
2. What is the role of the seminal vesicles and
the prostate gland?
3. What are the changes seen in girls at the
time of puberty?
4. How does the embryo get nourishment
inside the mother’s body?
5. If a woman is using a copper-T, will it help
in protecting her from sexually transmitted
diseases?
What you have learnt
gReproduction, unlike other life processes, is not essential to maintain the life of an
individual organism.
gReproduction involves creation of a DNA copy and additional cellular apparatus by the cell
involved in the process.
gVarious organisms use different modes of reproduction depending on their body design.
gIn ssion, many bacteria and protozoa simply divide into two or more daughter cells.
gOrganisms such as hydra can regenerate if they are broken into pieces. They can also give
out buds which mature into new individuals.
gRoots, stems and leaves of some plants develop into new plants through vegetative
propagation.
gThese are examples of asexual reproduction where new generations are created from a
single individual.
gSexual reproduction involves two individuals for the creation of a new individual.
gDNA copying mechanisms creates variations which are useful for ensuring the survival of
the species. Modes of sexual reproduction allow for greater variation to be generated.
gReproduction in owering plants involves transfer of pollen grains from the anther to the
stigma which is referred to as pollination. This is followed by fertilisation.
gChanges in the body at puberty, such as increase in breast size in girls and new facial hair
growth in boys, are signs of sexual maturation.
gThe male reproductive system in human beings consists of testes which produce sperms,
vas deferens, seminal vesicles, prostate gland, urethra and penis.
gThe female reproductive system in human beings consists of ovaries, fallopian tubes, uterus
and vagina.
gSexual reproduction in human beings involves the introduction of sperm in the vagina of
the female. Fertilisation occurs in the fallopian tube.
gContraception to avoid pregnancy can be achieved by the use of condoms, oral pills,
copper-T and other methods.
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and other problems if not performed properly.
Surgery can also be used for removal of
unwanted pregnancies. These may be misused
by people who do not want a particular child, as
happens in illegal sex-selective abortion of
female foetuses. For a healthy society, the
female-male sex ratio must be maintained.
Because of reckless female foeticides, child sex
ratio is declining at an alarming rate in some
sections of our society, although prenatal sex
determination has been prohibited by law.
We have noted earlier that reproduction is
the process by which organisms increase their
populations. The rates of birth and death in a
given population will determine its size. The size
of the human population is a cause for concern
for many people. This is because an expanding
population makes it harder to improve
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everybody’s standard of living. However, if
inequality in society is the main reason for poor
standards of living for many people, the size of
the population is relatively unimportant. If we
look around us, what can we identify as the most
important reason(s) for poor living standards?
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¿±sÁD+(\T)>±eTq+yû{ì“|Ÿ]>·Dì+#á>·\+?

ANDHRA PRADESH | Biology : How do Organisms Reproduce? €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :JeÚ\Tç|ŸÔáT«ÔáÎÜïmý²ÈsÁT|ŸÚÔsTT?
86
87
EXERCISES
1. Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.
2. Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
3. The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
4. What are the advantages of sexual reproduction over asexual reproduction?
5. What are the functions performed by the testis in human beings?
6. Why does menstruation occur?
7. Draw a labelled diagram of the longitudinal section of a ower.
8. What are the different methods of contraception?
9. How are the modes for reproduction different in unicellular and multicellular organisms?
10. How does reproduction help in providing stability to populations of species?
11. What could be the reasons for adopting contraceptive methods?
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ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
88 89
n<ó‘«jáT+8
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8
Heredity

ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
90 91
W
e have seen that reproductive
processes give rise to new
individuals that are similar, but subtly different.
We have discussed how some amount of
variation is produced even during asexual
reproduction. And the number of successful
variations are maximised by the process of
sexual reproduction. If we observe a eld of
sugarcane we nd very little variations among
the individual plants. But in a number of
animals including human beings, which
reproduce sexually, quite distinct variations are
visible among different individuals. In this
chapter, we shall be studying the mechanism by
which variations are created and inherited.
8.1 ACCUMULATION OF VARIATION
DURING REPRODUCTION
Inheritance from the previous generation
provides both a common basic body design,
and subtle changes in it, for the next generation.
Now think about what would happen when this
new generation, in its turn, reproduces. The
second generation will have differences that
they inherit from the rst generation, as well as
newly created differences (Fig. 8.1).
Figure 8.1 would represent the situation if
a single individual reproduces, as happens in
asexual reproduction. If one bacterium divides,
and then the resultant two bacteria divide again,
the four individual bacteria generated would be
very similar. There would be only very minor
differences between them, generated due to
small inaccuracies in DNA copying. However,
if sexual reproduction is involved, even greater
diversity will be generated, as we will see when
we discuss the rules of inheritance.
Do all these variations in a species have
equal chances of surviving in the environment
in which they nd themselves? Obviously not.
Depending on the nature of variations, different
individuals would have different kinds of
Figure 8.1
Creation of diversity over succeeding generations.
The original organism at the top will give rise to,
say, two individuals, similar in body design,
but with subtle differences. Each of them,
in turn, will give rise to two individuals in the
next generation. Each of the four individuals in
the bottom row will be different from each other.
While some of these differences will be unique,
others will be inherited from their respective
parents, who were different from each other.
advantages. Bacteria that can withstand heat
will survive better in a heat wave, as we have
discussed earlier. Selection of variants by
environmental factors forms the basis for
evolutionary processes, as we will discuss in
later sections.
8.2 HEREDITY
The most obvious outcome of the reproductive
process still remains the generation of
individuals of similar design. The rules of
heredity determine the process by which traits
and characteristics are reliably inherited. Let us
take a closer look at these rules.
8.2.1 Inherited Traits
What exactly do we mean by similarities and
differences? We know that a child bears all the
basic features of a human being. However, it
does not look exactly like its parents, and
1. If a trait A exists in 10% of a population of
an asexually reproducing species and a trait
B exists in 60% of the same population,
which trait is likely to have arisen earlier?
2. How does the creation of variations in a
species promote survival?
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ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
92 93
human populations show a great deal of
variation.
Mendel was educated in a
monastery and went on to
study science and mathematics
at the University of Vienna.
Failure in the examinations for
a teaching certicate did not
suppress his zeal for scientic
quest. He went back to his
monastery and started growing peas. Many
others had studied the inheritance of traits in
peas and other organisms earlier, but Mendel
blended his knowledge of science and
mathematics and was the rst one to keep
count of individuals exhibiting a particular
trait in each generation. This helped him to
arrive at the laws of inheritance.
gObserve the ears of all the students in the
class. Prepare a list of students having
free or attached earlobes and calculate the
percentage of students having each (Fig.
8.2). Find out about the earlobes of the
parents of each student in the class.
Correlate the earlobe type of each student
with that of their parents. Based on this
evidence, suggest a possible rule for the
inheritance of earlobe types.
Activity 8.1
(a) (b)
Figure 8.2
(a) Free and (b) attached earlobes. The lowest part of
the ear, called the earlobe, is closely attached to the
side of the head in some of us, and not in others. Free
and attached earlobes are two variants found in human
populations.
Mendel used a number of contrasting visible
characters of garden peas–round/wrinkled seeds,
tall/short plants, white/violet owers and so on.
He took pea plants with different characteristics
–a tall plant and a short plant, produced progeny
by crossing them, and calculated the percentages
of tall or short progeny.
In the rst place, there were no halfway
characteristics in this rst-generation, or F1
progeny –no ‘medium-height’ plants. All plants
were tall. This meant that only one of the parental
traits was seen, not some mixture of the two. So the
next question was, were the tall plants in the F1
generation exactly the same as the tall plants of the
parent generation? Mendelian experiments test
this by getting both the parental plants and these F1
tall plants to reproduce by self-pollination. The
progeny of the parental plants are, of course, all
tall. However, the second-generation, or F2,
progeny of the F1 tall plants are not all tall. Instead,
one quarter of them are short. This indicates that
both the tallness and shortness traits were inherited
in the F1 plants, but only the tallness trait was
expressed. This led Mendel to propose that two
copies of factor (now called genes) controlling
traits are present in sexually reproducing
organism. These two may be identical, or may be
different, depending on the parentage. A pattern of
inheritance can be worked out with this
assumption, as shown in Fig. 8.3.
8.2.2 Rules for the Inheritance of Traits –
Mendel’s Contributions
The rules for inheritance of such traits in
human beings are related to the fact that both
the father and the mother contribute practically
equal amounts of genetic material to the child.
This means that each trait can be inuenced by
both paternal and maternal DNA. Thus, for
each trait there will be two versions in each
child. What will, then, the trait seen in the child
be? Mendel (see box) worked out the main
rules of such inheritance, and it is interesting to
look at some of his experiments from more
than a century ago.
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ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
94 95
Figure 8.3
Inheritance of traits over two generations
Activity 8.2
gIn Fig. 8.3, what experiment would we
do to conrm that the F2 generation did
in fact have a 1:2:1 ratio of TT, Tt and tt
trait combinations?
In this explanation, both TT and Tt are tall
plants, while only tt is a short plant. In other
words, a single copy of ‘T’ is enough to make
the plant tall, while both copies have to be ‘t’ for
the plant to be short. Traits like ‘T’ are called
dominant traits, while those that behave like ‘t’
are called recessive traits. Work out which trait
would be considered dominant and which one
recessive in Fig. 8.4.
What happens when pea plants showing
two different characteristics, rather than just
one, are bred with each other? What do the
progeny of a tall plant with round seeds and a
short plant with wrinkled-seeds look like? They
are all tall and have round seeds. Tallness and
round seeds are thus dominant traits. But what
happens when these F1 progeny are used to
generate F2 progeny by self-pollination? A
Mendelian experiment will nd that some F2
progeny are tall plants with round seeds, and
some were short plants with wrinkled seeds.
However, there would also be some F2 progeny
that showed new combinations. Some of them
would be tall, but have wrinkled seeds, while
others would be short, but have round seeds.
You can see as to how new combinations of
traits are formed in F2 offspring when factors
controlling for seed shape and seed colour
recombine to form zygote leading to form F2
offspring (Fig. 8.5). Thus, the tall/short trait and
the round seed/wrinkled seed trait are
independently inherited.
8.2.3 How do these Traits get Expressed?
How does the mechanism of heredity
work? Cellular DNA is the information source
for making proteins in the cell. A section of
DNA that provides information for one protein
is called the gene for that protein. How do
proteins control the characteristics that we are
discussing here? Let us take the example of
tallness as a characteristic. We know that plants
have hormones that can trigger growth. Plant
height can thus depend on the amount of a
particular plant hormone. The amount of the
plant hormone made will depend on the
efciency of the process for making it.
Consider now an enzyme that is important for
this process. If this enzyme works efciently, a
lot of hormone will be made, and the plant will
be tall. If the gene for that enzyme has an
alteration that makes the enzyme less efcient,
the amount of hormone will be less, and the
plant will be short. Thus, genes control
characteristics, or traits.
If the interpretations of Mendelian
experiments we have been discussing are
correct, then both parents must be contributing
equally to the DNA of the progeny during
sexual reproduction. We have disscussed this
issue in the previous Chapter. If both parents
can help determine the trait in the progeny, both
parents must be contributing a copy of the same
gene. This means that each pea plant must have
two sets of all genes, one inherited from each
parent. For this mechanism to work, each germ
cell must have only one gene set.
How do germ-cells make a single set of
genes from the normal two copies that all other
cells in the body have? If progeny plants
inherited a single whole gene set from each
parent, then the experiment explained in Fig.
8.5 cannot work. This is because the two
characteristics ‘R’ and ‘y’ would then be linked
to each other and cannot be independently
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ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
96 97
inherited. This is explained by the fact that each
gene set is present, not as a single long thread of
DNA, but as separate independent pieces, each
called a chromosome. Thus, each cell will have
two copies of each chromosome, one each from
the male and female parents. Every germ-cell
will take one chromosome from each pair and
these may be of either maternal or paternal
origin. When two germ cells combine, they will
restore the normal number of chromosomes in
the progeny, ensuring the stability of the DNA
of the species. Such a mechanism of inheritance
explains the results of the Mendel experiments,
and is used by all sexually reproducing
organisms. But asexually reproducing
organisms also follow similar rules of
inheritance. Can we work out how their
inheritance might work?
8.2.4 Sex Determination
We have discussed the idea that the two sexes
participating in sexual reproduction must be
somewhat different from each other for a
number of reasons. How is the sex of a newborn
individual determined? Different species use
very different strategies for this. Some rely
entirely on environmental cues. Thus, in some
animals like a few reptiles, the temperature at
which fertilised eggs are kept determines
whether the animals developing in the eggs will
be male or female. In other animals, such as
snails, individuals can change sex, indicating
that sex is not genetically determined.
However, in human beings, the sex of the
individual is largely genetically determined. In
other words, the genes inherited from our
parents decide whether we will be boys or girls.
But so far, we have assumed that similar gene
sets are inherited from both parents. If that is
the case, how can genetic inheritance determine
sex?
The explanation lies in the fact that all
human chromosomes are not paired. Most
human chromosomes have a maternal and a
paternal copy, and we have 22 such pairs. But
one pair, called the sex chromosomes, is odd in
not always being a perfect pair. Women have a
perfect pair of sex chromosomes, both called X.
But men have a mismatched pair in which one
is a normal-sized X while the other is a short Figure 8.5
Independent inheritance
of two separate traits, shape and colour of seeds
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ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
98 99
one called Y. So women are XX, while men are
XY. Now, can we work out what the inheritance
pattern of X and Y will be?
As Fig. 8.6 shows, half the children will
be boys and half will be girls. All children will
inherit an X chromosome from their mother
regardless of whether they are boys or girls.
Thus, the sex of the children will be determined
by what they inherit from their father. A child
who inherits an X chromosome from her father
will be a girl, and one who inherits a Y
chromosome from him will be a boy.
1. How do Mendel’s experiments show that
traits may be dominant or recessive?
2. How do Mendel’s experiments show that
traits are inherited independently?
3. A man with blood group A marries a
woman with blood group O and their
daughter has blood group O. Is this
information enough to tell you which of
the traits – blood group A or O – is
dominant? Why or why not?
4. How is the sex of the child determined in
human beings?
What you have learnt
gVariations arising during the process of reproduction can be inherited.
gThese variations may lead to increased survival of the individuals.
gSexually reproducing individuals have two copies of genes for the same trait. If the copies
are not identical, the trait that gets expressed is called the dominant trait and the other is
called the recessive trait.
gTraits in one individual may be inherited separately, giving rise to new combinations of traits
in the offspring of sexual reproduction.
gSex is determined by different factors in various species. In human beings, the sex of the
child depends on whether the paternal chromosome is X (for girls) or Y (for boys).
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Figure 8.6
Sex determination in human beings
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MTsÁT@$THûsÁTÌÅ£”H•sÁT?

ANDHRA PRADESH | Biology : Heredity €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ :nqTe+¥¿£Ôá
100 101
EXERCISES
1. A Mendelian experiment consisted of breeding tall pea plants bearing violet owers with
short pea plants bearing white owers. The progeny all bore violet owers, but almost half
of them were short. This suggests that the genetic make-up of the tall parent can be
depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
2. A study found that children with light-coloured eyes are likely to have parents with light-
coloured eyes. On this basis, can we say anything about whether the light eye colour trait
is dominant or recessive? Why or why not?
3. Outline a project which aims to nd the dominant coat colour in dogs.
4. How is the equal genetic contribution of male and female parents ensured in the progeny?
nuó²«kÍ\T
1. ÿ¿£yîT+&ƒýÙç|ŸjîÖ>·+ýË}<‘sÁ+>·T|ŸÚcÍÎ\qT¿£*Ðqbõ&ƒy{ì‹sÄD¡yîTT¿£Ø\qTÔî\T|ŸÚsÁ+>·T|ŸÚcÍÎ\qT¿£*Ðqbõ{ì¼
‹sÄD¡yîTT¿£Ø\ÔÃç|ŸÈÈq+#ûjáT‹&q~.dŸ+ÔáÜyîTT¿£Ø\ú•}<‘sÁ+>·T|ŸÚcÍÎ\qT¿£*Ð–H•sTT.nsTTÔûy{ìýË<‘<‘|ŸÚ
dŸ>·+bõ{ì¼yîTT¿£Ø\T@sÁÎ&†¦sTT.B““‹{ì¼dŸÖº+#á‹&qbõ&ƒy{ìÈq¿£yîTT¿£Ø\ÈqT«sÁÖ|Ÿ+‡$<óŠ+>±e]’+#áe#áTÌ.
(m) TTWW
(_) TTww
(d¾) TtWW
(&) TtWw
2. ýñÔásÁ+>·T¿£ÞøßqT¿£*Ðq|¾\¢\ÈqÅ£”\TÅ£L&†ýñÔásÁ+>·T¿£ÞøßqT¿£*Ð–+{²sÁ“ÿ¿£n<óŠ«jáTq+ýË¿£qT>=q‹&+~.B“
€<ó‘sÁ+>±ýñÔásÁ+>·T¿£Þø—ßnHû\¿£ŒD+‹V¾²sÁZÔá\¿£ŒDeÖýñ<‘n+ÔásÁZÔá\¿£ŒDeÖn“#î|ŸÎe#Ì?m+<ŠTÅ£”ýñ<‘m+<ŠTÅ£”
#î|ŸÎýñeTT?
3. Å£”¿£Ø\u¤#áTÌsÁ+>·TjîTT¿£Ø‹V¾²sÁZÔá\¿£ŒD²“•¿£qT>=Hû–<ûÝXø«+ÔÃÿ¿£çbÍCÉÅ£”¼qT“sÁÇV¾²+#á+&.
4. Ôá*¢<Š+ç&ƒT\qT+&dŸ+ÔáÜ¿ìdŸeÖq+>±ÈqT«|Ÿ<‘sÁœ+mý²n+~+#á‹&ƒTÔáT+~?

ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
104 105
W
e have heard the word
‘environment’ often being used on
the television, in newspapers and by people
around us. Our elders tell us that the
‘environment’ is not what it used to be earlier;
others say that we should work in a healthy
‘environment’; and global summits involving
the developed and developing countries are
regularly held to discuss ‘environmental’
issues. In this chapter, we shall be studying how
various components in the environment
interact with each other and how we impact the
environment.
13.1 ECO-SYSTEM — WHAT ARE ITS
COMPONENTS?
All organisms such as plants, animals,
microorganisms and human beings as well as
the physical surroundings interact with each
other and maintain a balance in nature. All the
interacting organisms in an area together with
the non-living constituents of the environment
form an ecosystem. Thus, an ecosystem
consists of biotic components comprising
living organisms and abiotic components
comprising physical factors like temperature,
rainfall, wind, soil and minerals.
For example, if you visit a garden you
will nd different plants, such as grasses, trees;
ower bearing plants like rose, jasmine,
sunower; and animals like frogs, insects and
birds. All these living organisms interact with
each other and their growth, reproduction and
other activities are affected by the abiotic
components of ecosystem. So a garden is an
ecosystem. Other types of ecosystems are
forests, ponds and lakes. These are natural
ecosystems while gardens and crop-elds are
human-made (articial) ecosystems.
Activity 13.1
gYou might have seen an aquarium. Let us
try to design one.
gWhat are the things that we need to keep
in mind when we create an aquarium?
The sh would need a free space for
swimming (it could be a large jar), water,
oxygen and food.
gWe can provide oxygen through an
oxygen pump (aerator) and sh food
which is available in the market.
gIf we add a few aquatic plants and
animals it can become a self-sustaining
system. Can you think how this happens?
An aquarium is an example of a human-
made ecosystem.
gCan we leave the aquarium as such after
we set it up? Why does it have to be
cleaned once in a while? Do we have to
clean ponds or lakes in the same manner?
Why or why not?
We have seen in earlier classes that
organisms can be grouped as producers,
consumers and decomposers according to the
manner in which they obtain their sustenance
from the environment. Let us recall what we
have learnt through the self sustaining
ecosystem created by us above. Which
organisms can make organic compounds like
sugar and starch from inorganic substances
using the radiant energy of the Sun in the
presence of chlorophyll? All green plants and
certain bacteria which can produce food by
photosynthesis come under this category and
are called the producers.
Organisms depend on the producers
either directly or indirectly for their
sustenance? These organisms which consume
the food produced, either directly from
producers or indirectly by feeding on other
consumers are the consumers. Consumers can
be classed variously as herbivores, carnivores,
omnivores and parasites. Can you give
examples for each of these categories of
consumers?
gImagine the situation where you do not
clean the aquarium and some sh and
plants have died. Have you ever thought
what happens when an organism dies? The
microorganisms, comprising bacteria and
fungi, break-down the dead remains and
waste products of organisms. These
microorganisms are the decomposers as
they break-down the complex organic
substances into simple inorganic
substances that go into the soil and are used
up once more by the plants. What will
happen to the garbage, and dead animals
and plants in their absence? Will the
natural replenishment of the soil take
place, even if decomposers are not there?
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ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
106 107
Activity 13.2
gWhile creating an aquarium did you take
care not to put an aquatic animal which
would eat others? What would have
happened otherwise?
gMake groups and discuss how each of the
above groups of organisms are dependent
on each other.
gWrite the aquatic organisms in order of
who eats whom and form a chain of at
least three steps.
gWould you consider any one group of
organisms to be of primary importance?
Why or why not?
13.1.1 Food Chains and Webs
In Activity 13.2 we have formed a series
of organisms feeding on one another. This
series or organisms taking part at various biotic
levels form a food chain (Fig. 13.1).
Each step or level of the food chain forms
a trophic level. The autotrophs or the producers
are at the rst trophic level. They x up the solar
energy and make it available for heterotrophs or
the consumers. The herbivores or the primary
consumers come at the second, small
carnivores or the secondary consumers at the
third and larger carnivores or the tertiary
consumers form the fourth trophic level (Fig.
13.2).
We know that the food we eat acts as a
fuel to provide us energy to do work. Thus the
interactions among various components of the
environment involves ow of energy from one
component of the system to another. As we
have studied, the autotrophs capture the energy
present in sunlight and convert it into chemical
energy. This energy supports all the activities of
the living world. From autotrophs, the energy
goes to the heterotrophs and decomposers.
However, as we saw in the previous Chapter on
‘Sources of Energy’, when one form of energy
is changed to another, some energy is lost to the
environment in forms which cannot be used
again. The ow of energy between various
components of the environment has been
extensively studied and it has been found that –
gThe green plants in a terrestrial ecosystem
capture about 1% of the energy of sunlight
that falls on their leaves and convert it into
food energy.
gWhen green plants are eaten by primary
consumers, a great deal of energy is lost as
heat to the environment, some amount goes
into digestion and in doing work and the
rest goes towards growth and reproduction.
An average of 10% of the food eaten is
turned into its own body and made
available for the next level of consumers.
gTherefore, 10% can be taken as the average
value for the amount of organic matter that
is present at each step and reaches the next
level of consumers.
gSince so little energy is available for the
next level of consumers, food chains
generally consist of only three or four
steps. The loss of energy at each step is so
great that very little usable energy remains
after four trophic levels.
gThere are generally a greater number of
individuals at the lower trophic levels of an
ecosystem, the greatest number is of the
producers.
Figure 13.1
Food chain in nature
(a) in forest, (b) in grassland and (c) in a pond
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(d¾)

ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
108 109
gThe length and complexity of food chains
vary greatly. Each organism is generally
eaten by two or more other kinds of
organisms which in turn are eaten by
several other organisms. So instead of a
straight line food chain, the relationship
can be shown as a series of branching lines
called a food web (Fig. 13.3).
From the energy ow diagram (Fig.
13.4), two things become clear. Firstly, the ow
of energy is unidirectional. The energy that is
captured by the autotrophs does not revert back
to the solar input and the energy which passes to
the herbivores does not come back to
autotrophs. As it moves progressively through
the various trophic levels it is no longer
available to the previous level. Secondly, the
energy available at each trophic level gets
diminished progressively due to loss of energy
at each level.
Another interesting aspect of food chain
is how unknowingly some harmful chemicals
enter our bodies through the food chain. You
have read in Class IX how water gets polluted.
One of the reasons is the use of several
pesticides and other chemicals to protect our
crops from diseases and pests. These chemicals
are either washed down into the soil or into the
water bodies. From the soil, these are absorbed
by the plants along with water and minerals,
and from the water bodies these are taken up by
aquatic plants and animals. This is one of the
ways in which they enter the food chain. As
these chemicals are not degradable, these get
accumulated progressively at each trophic
level. As human beings occupy the top level in
any food chain, the maximum concentration of
these chemicals get accumulated in our bodies.
This phenomenon is known as biological
Figure 13.2 Trophic levels
Figure 13.3
Food web, consisting of many food chains
Figure 13.4
Diagram showing ow of energy in an ecosystem
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ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
110 111
Activity 13.3
gNewspaper reports about pesticide levels
in ready-made food items are often seen
these days and some states have banned
these products. Debate in groups the
need for such bans.
gWhat do you think would be the source
of pesticides in these food items? Could
pesticides get into our bodies from this
source through other food products too?
gDiscuss what methods could be applied
to reduce our intake of pesticides.
1. What are trophic levels? Give an example
of a food chain and state the different
trophic levels in it.
2. What is the role of decomposers in the
ecosystem?
13.2 HOW DO OUR ACTIVITIES
AFFECT THE ENVIRONMENT?
We are an integral part of the environment.
Changes in the environment affect us and our
activities change the environment around us.
We have already seen in Class IX how our
activities pollute the environment. In this
chapter, we shall be looking at two of the
environmental problems in detail, that is,
depletion of the ozone layer and waste disposal.
13.2.1 Ozone Layer and How it is Getting
Depleted
Ozone (O ) is a molecule formed by three atoms
3
of oxygen. While O , which we normally refer
2
to as oxygen, is essential for all aerobic forms
of life. Ozone, is a deadly poison. However, at
the higher levels of the atmosphere, ozone
performs an essential function. It shields the
surface of the earth from ultraviolet (UV)
13.2.2 Managing the Garbage we Produce
In our daily activities, we generate a lot of
material that are thrown away. What are some
of these waste materials? What happens after
we throw them away? Let us perform an
activity to nd answers to these questions.
radiation from the Sun. This radiation is highly
damaging to organisms, for example, it is
known to cause skin cancer in human beings.
Ozone at the higher levels of the
atmosphere is a product of UV radiation acting
on oxygen (O ) molecule. The higher energy
2
UV radiations split apart some moleculer
oxygen (O ) into free oxygen (O) atoms. These
2
atoms then combine with the molecular oxygen
to form ozone as shown—
The amount of ozone in the atmosphere
began to drop sharply in the 1980s. This
decrease has been linked to synthetic chemicals
like chlorouorocarbons (CFCs) which are
used as refrigerants and in re extinguishers. In
1987, the United Nations Environment
Programme (UNEP) succeeded in forging an
agreement to freeze CFC production at 1986
levels. It is now mandatory for all the
manufacturing companies to make CFC-free
refrigerators throughout the world.
magnication. This is the reason why our food
grains such as wheat and rice, vegetables and
fruits, and even meat, contain varying amounts
of pesticide residues. They cannot always be
removed by washing or other means.
2 3
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Activity 13.4
gFind out from the library, internet or
newspaper reports, which chemicals are
responsible for the depletion of the ozone
layer.
gFind out if the regulations put in place to
control the emission of these chemicals
have succeeded in reducing the damage to
the ozone layer. Has the size of the hole in
the ozone layer changed in recent years?
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¿£Ô«“•#û<‘Ý+.

ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
110 111
Activity 13.3
gNewspaper reports about pesticide levels
in ready-made food items are often seen
these days and some states have banned
these products. Debate in groups the
need for such bans.
gWhat do you think would be the source
of pesticides in these food items? Could
pesticides get into our bodies from this
source through other food products too?
gDiscuss what methods could be applied
to reduce our intake of pesticides.
1. What are trophic levels? Give an example
of a food chain and state the different
trophic levels in it.
2. What is the role of decomposers in the
ecosystem?
13.2 HOW DO OUR ACTIVITIES
AFFECT THE ENVIRONMENT?
We are an integral part of the environment.
Changes in the environment affect us and our
activities change the environment around us.
We have already seen in Class IX how our
activities pollute the environment. In this
chapter, we shall be looking at two of the
environmental problems in detail, that is,
depletion of the ozone layer and waste disposal.
13.2.1 Ozone Layer and How it is Getting
Depleted
Ozone (O) is a molecule formed by three atoms
3
of oxygen. While O, which we normally refer
2
to as oxygen, is essential for all aerobic forms
of life. Ozone, is a deadly poison. However, at
the higher levels of the atmosphere, ozone
performs an essential function. It shields the
surface of the earth from ultraviolet (UV)
13.2.2 Managing the Garbage we Produce
In our daily activities, we generate a lot of
material that are thrown away. What are some
of these waste materials? What happens after
we throw them away? Let us perform an
activity to nd answers to these questions.
radiation from the Sun. This radiation is highly
damaging to organisms, for example, it is
known to cause skin cancer in human beings.
Ozone at the higher levels of the
atmosphere is a product of UV radiation acting
on oxygen (O) molecule. The higher energy
2
UV radiations split apart some moleculer
oxygen (O) into free oxygen (O) atoms. These
2
atoms then combine with the molecular oxygen
to form ozone as shown—
The amount of ozone in the atmosphere
began to drop sharply in the 1980s. This
decrease has been linked to synthetic chemicals
like chlorouorocarbons (CFCs) which are
used as refrigerants and in re extinguishers. In
1987, the United Nations Environment
Programme (UNEP) succeeded in forging an
agreement to freeze CFC production at 1986
levels. It is now mandatory for all the
manufacturing companies to make CFC-free
refrigerators throughout the world.
magnication. This is the reason why our food
grains such as wheat and rice, vegetables and
fruits, and even meat, contain varying amounts
of pesticide residues. They cannot always be
removed by washing or other means.
2 3
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Activity 13.4
gFind out from the library, internet or
newspaper reports, which chemicals are
responsible for the depletion of the ozone
layer.
gFind out if the regulations put in place to
control the emission of these chemicals
have succeeded in reducing the damage to
the ozone layer. Has the size of the hole in
the ozone layer changed in recent years?
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¿£Ô«“•#û<‘Ý+.

ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
112 113
Activity 13.5 Activity 13.6
gCollect waste material from your homes.
This could include all the waste
generated during a day, like kitchen
waste (spoilt food, vegetable peels, used
tea leaves, milk packets and empty
cartons), waste paper, empty medicine
bottles/strips/bubble packs, old and torn
clothes and broken footwear.
gBury this material in a pit in the school
garden or if there is no space available,
you can collect the material in an old
bucket/ower pot and cover with at least
15 cm of soil.
gKeep this material moist and observe at
15-day intervals.
gWhat are the materials that remain
unchanged over long periods of time?
gWhat are the materials which change
their form and structure over time?
gOf these materials that are changed,
which ones change the fastest?
gUse the library or internet to nd out
more about biodegradable and non-
biodegradable substances.
gHow long are various nonbiodegradable
substances expected to last in our
environment?
gThese days, new types of plastics which
are said to be biodegradable are
available. Find out more about such
materials and whether they do or do not
harm the environment.
We have seen in the chapter on ‘Life
Processes’ that the food we eat is digested by
various enzymes in our body. Have you ever
wondered why the same enzyme does not
break-down everything we eat? Enzymes are
specic in their action, specic enzymes are
needed for the break-down of a particular
substance. That is why we will not get any
energy if we try to eat coal! Because of this,
many human-made materials like plastics will
not be broken down by the action of bacteria or
other saprophytes. These materials will be
acted upon by physical processes like heat and
pressure, but under the ambient conditions
found in our environment, these persist for a
long time.
Substances that are broken down by
biological processes are said to be
biodegradable. How many of the substances
you buried were biodegradable? Substances
that are not broken down in this manner are said
to be non-biodegradable. These substances
may be inert and simply persist in the
environment for a long time or may harm the
various members of the eco-system.
1. Why are some substances biodegradable
and some non-biodegradable?
2. Give any two ways in which
biodegradable substances would affect
the environment.
3. Give any two ways in which non-
biodegradable substances would affect
the environment.
Visit any town or city, and we are sure to
nd heaps of garbage all over the place. Visit
any place of tourist interest and we are sure to
nd the place littered with empty food
wrappers. In the earlier classes we have talked
about this problem of dealing with the garbage
that we generate. Let us now look at the
problem a bit more deeply.
Activity 13.7
gFind out what happens to the waste
generated at home. Is there a system in
place to collect this waste?
gFind out how the local body (panchayat,
municipal corporation, resident welfare
association) deals with the waste. Are
there mechanisms in place to treat the
biodegradable and non-biodegradable
wastes separately?
gCalculate how much waste is generated
at home in a day.
gHow much of this waste is
biodegradable?
gCalculate how much waste is generated
in the classroom in a day.
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ç|Ÿ Xø• \T

ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
114 115
gHow much of this waste is biodegradable?
gSuggest ways of dealing with this waste.
Activity 13.8
Activity 13.9
gFind out how the sewage in your locality
is treated. Are there mechanisms in place
to ensure that local water bodies are not
polluted by untreated sewage.
gFind out how the local industries in your
locality treat their wastes. Are there
mechanisms in place to ensure that the
soil and water are not polluted by this
waste?
gSearch the internet or library to nd out
what hazardous materials have to be
dealt with while disposing of electronic
items. How would these materials affect
the environment?
gFind out how plastics are recycled. Does
the recycling process have any impact
on the environment?
Improvements in our life-style have
resulted in greater amounts of waste material
generation. Changes in attitude also have a role
to play, with more and more things we use
becoming disposable. Changes in packaging
Think it over
What you have learnt
Disposable cups in trains
If you ask your parents, they will probably remember a time when tea in trains was served in
plastic glasses which had to be returned to the vendor. The introduction of disposable cups was
hailed as a step forward for reasons of hygiene. No one at that time perhaps thought about the
impact caused by the disposal of millions of these cups on a daily basis. Some time back, kulhads,
that is, disposable cups made of clay, were suggested as an alternative. But a little thought
showed that making these kulhads on a large scale would result in the loss of the fertile top-soil.
Now disposable paper-cups are being used. What do you think are the advantages of disposable
paper-cups over disposable plastic cups?
gThe various components of an ecosystem are interdependent.
gThe producers make the energy from sunlight available to the rest of the ecosystem.
gThere is a loss of energy as we go from one trophic level to the next, this limits the number of
trophic levels in a food-chain.
gHuman activities have an impact on the environment.
gThe use of chemicals like CFCs has endangered the ozone layer. Since the ozone layer
protects against the ultraviolet radiation from the Sun, this could damage the environment.
gThe waste we generate may be biodegradable or non-biodegradable.
gThe disposal of the waste we generate is causing serious environmental problems.
1. What is ozone and how does it affect any
ecosystem?
2. How can you help in reducing the
problem of waste disposal? Give any two
methods.
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ç|Ÿuó²$Ôá+#ûdŸTï+~?
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have resulted in much of our waste becoming
non-biodegradable. What do you think will be
the impact of these on our environment?
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ANDHRA PRADESH | Biology : Our Environment €+ç<óŠç|Ÿ<ûXÙ | JeXæçdŸï+ : eTq|Ÿs«esÁD+
116 117
EXERCISES
1. Which of the following groups contain only biodegradable items?
(a) Grass, owers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, sh and goat
3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
4. What will happen if we kill all the organisms in one trophic level?
5. Will the impact of removing all the organisms in a trophic level be different for different
trophic levels? Can the organisms of any trophic level be removed without causing any
damage to the ecosystem?
6. What is biological magnication? Will the levels of this magnication be different at different
levels of the ecosystem?
7. What are the problems caused by the non-biodegradable wastes that we generate?
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this
damage?
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118
Learning Outcomes at the Secondary Stage
Class X
Suggested Pedagogical Processes Learning Outcomes
The learners may be provided with
opportunities individually or in groups
and encouraged to —
y recognise the difference between
reactions, such as, exothermic and
endothermic, oxidation and reduction,
etc.
y observe to understand the difference in
the temperatures in both the reactions
using laboratory thermometer.
y investigate the ways of segregation of
waste material on the basis of their
degradation property. They may be
encouraged to practice the segregation
of waste before disposal at home,
school, and public places.
y explore the relationship between two
physical quantities, such as, between
potential difference across a conductor
and electric current flowing through it;
design, conduct, and share the findings
of an activity
y find out ‘why’ and ‘how’ of processes or
phenomena, such as, transportation in
plants and animals, extraction of metals
from ores, with the help of activities,
experiments, and demonstration. The
learners may be encouraged to discuss,
relate, conclude and explain processes
or phenomena to their peers using
interdisciplinary approach.
y observe diagrams, such as that of
digestive system and the names given
to various organs. The learners may be
motivated to make poster of the digestive
system for displaying in school. They
may also be provided opportunities to
use ICT tools for drawing.
y collect wide variety of graphs from
newspapers, magazines, or the
internet, with a view to understand
the information contained therein. The
learners may be facilitated to draw a
graph, such as V-I graph for analysing
the relationship between the potential
difference across a conductor and the
current through it.
The learner —
y differentiates materials, objects,
organisms, phenomena, and
processes, based on, properties and
characteristics, such as, autotrophic
and heterotrophic nutrition,
biodegradable and non-biodegradable
substances, various types of reactions,
strong and weak acids and bases,
acidic, basic, and neutral salts using
different indicators, real and virtual
images, etc.
y classifies materials, objects,
organisms, phenomena, and
processes, based on properties and
characteristics, such as, metals and
non-metals, acid and bases on the
basis of their physical and chemical
properties.
y plans and conducts investigations and
experiments to arrive at and verify
the facts, principles, phenomena,
or to seek answers to queries on
their own, such as, investigates
conditions necessary for rusting, tests
the conductivity of various solutions,
compares the foaming capacity of
different types of soap samples, verifies
laws of reflection and refraction of light,
Ohm’s law, etc. Do variegated leaves
perform photosynthesis? Which gas is
evolved during fermentation? Why does
the shoot of a plant moves towards
light?
y relates processes and phenomena
with causes and effects, such as,
hormones with their functions, tooth
decay with pH of saliva, growth of plants
with pH of the soil, survival of aquatic
life with pH of water, blue colour of sky
with scattering of light, deflection of
compass needle due to magnetic effect
of electric current, etc.
y explains processes and phenomena,
such as, nutrition in human beings
and plants, transportation in plants

119
Learning Outcomes for Science
y study how chemical equations are
balanced using simple mathematical
skills. Discussion may be conducted
on the significance of balancing of
chemical equations.
y get familiar with New Cartesian Sign
Convention using illustrated cards and
may be given ample opportunities to
apply the sign convention in various
situations of reflection by spherical
mirrors.
y perform a role-play on ecosystem in a
hypothetical situation, such as, what
will happen if all herbivores suddenly
vanish from earth. This may be followed
by a discussion about how the loss of
biodiversity disrupts the food chain
hereby adversely affecting the energy
flow in an ecosystem.
y derive equations, formulae, laws, etc.
For example, the derivation for formula
of the equivalent resistance of resistors
in series (or parallel). They should be
encouraged to practice the derivation
till they are confident.
y study the features inherited through
genes, such as, attached or free
earlobes. They may be encouraged to
observe and compare the earlobes of
their friends with the earlobes of their
parents and grandparents to arrive at
the conclusion that characters or traits
are inherited in offsprings from their
parents.
y collect print and non-print materials by
exploring the library and the internet
about scientists and their findings to
appreciate how concepts evolved with
time. They may be motivated to share
their findings by preparing posters and
performing role plays or skits.
y encourage learners to visit science
museums, biodiversity parks, aviaries,
zoological parks, botanical gardens,
fisheries, poultry farms, factories, etc.
and animals, extraction of metals from
ores, placement of elements in modern
periodic table, displacement of metals
from their salt solutions on the basis
of reactivity series, working of electric
motor and generator, twinkling of stars,
advanced sunrise and delayed sunset,
formation of rainbow, etc.
y draws labelled diagrams, flow charts,
concept maps, and graphs, such
as, digestive, respiratory, circulatory,
excretory, and reproductive systems,
electrolysis of water, electron dot
structure of atoms and molecules, flow
chart for extraction of metals from ores,
ray diagrams, magnetic field lines, etc.
y analyses and interprets data,
graphs, and figures, such as, melting
and boiling points of substances to
differentiate between covalent and ionic
compounds, pH of solutions to predict
the nature of substances, V-I graphs,
ray diagrams, etc.
y calculates using the data given,
such as, number of atoms in reactants
and products to balance a chemical
equation, resistance of a system of
resistors, power of a lens, electric
power, etc.
y uses scientific conventions to
represent units of various quantities,
symbols, formulae, and equations,
such as, balanced chemical equation
by using symbols and physical states of
substances, sign convention in optics,
SI units, etc.
y handles tools and laboratory
apparatus properly; measures
physical quantities using appropriate
apparatus, instruments, and
devices, such as, pH of substances
using pH paper, electric current and
potential difference using ammeter and
voltmeter, etc.

120
Learning Outcomes at the Secondary Stage
y collect eco-friendly, commonly available
materials to design and develop
technological devices and innovative
exibits, such as, electric motor, soda
acid fire extinguisher, respiratory
system, etc. They may be motivated
to display their exhibits or models
in science exhibitions, science club,
classrooms, during parent-teacher
meet and to respond to the queries
raised during interaction.
y visit classrooms, laboratories, library,
toilets, playground, etc., to identify
places where wastage of electricity and
water may be occurring. Discussion
may be held on importance of natural
resources and their conservation,
leading to the conviction for adoption
of good habits in their day-to-day
life. The learners may also organise
a sensitisation programme on such
issues.
y share their findings of the activities,
projects, and experiments, such as,
extraction of metals from ores, working
of electric motor and generator,
formation of rainbow, etc., in oral and
written forms. Report writing may be
facilitated to share their findings by
using appropriate technical terms,
figures, tables, graphs, etc. They may
be encouraged to draw conclusions on
the basis of their observations.
y applies learning to hypothetical
situations, such as, what will happen
if all herbivores are removed from an
ecosystem? What will happen if all
non-renewable sources of energy are
exhausted?
y applies scientific concepts in daily
life and solving problems, such as,
suggest precautions to prevent sexually
transmitted infections, uses appropriate
electrical plugs (5/15A) for different
electrical devices, uses vegetative
propagation to develop saplings in
gardens, performs exercise to keep in
good health, avoids using appliances
responsible for ozone layer depletion,
applies concept of decomposition
reaction of baking soda to make spongy
cakes, etc.
y derives formulae, equations, and
laws, such as, equivalent resistance of
resistors in series and parallel, etc.
y draws conclusion, such as, traits or
features are inherited through genes
present on chromosomes, a new
species originates through evolutionary
processes, water is made up of hydrogen
and oxygen, properties of elements
vary periodically along the groups and
periods in periodic table, potential
difference across a metal conductor
is proportional to the electric current
flowing through it, etc.
y takes initiative to know about scientific
discoveries and inventions, such as,
Mendel’s contribution in understanding
the concept of inheritance, Dobereiner for
discovering triads of elements, Mendeleev
for the development of the periodic table
of elements, Oersted’s discovery that
electricity and magnetism are related,
discovery of relation between potential
difference across a metal conductor and
the electric current flowing through it by
Ohm, etc.
y exhibits creativity in designing
models using eco-friendly resources,
such as, working model of respiratory,

121
Learning Outcomes for Science
digestive, and excretory systems,
soda acid fire extinguisher,
periodic table, micelles formation,
formation of diamond, graphite, and
Buckminsterfullerene, human eye,
electric motor and generator, etc.
y exhibits values of honesty,
objectivity, rational thinking, and
freedom from myth and superstitious
beliefs while taking decisions,
respect for life, etc., such as,
reports and records experimental data
accurately, says no to consumption of
alcohol and drugs, sensitises others
about its effect on physical and
mental health, sensitises for blood
and organ donations, understands
the consequences of pre-natal sex
determination, etc.
y communicates the findings and
conclusions effectively, such as,
those derived from experiments,
activities, and projects orally and in
written form using appropriate figures,
tables, graphs, and digital forms, etc.
y makes efforts to conserve
environment realising the inter-
dependency and inter-relationship
in the biotic and abiotic factors of
environment, such as, appreciates
and promotes segregation of
biodegradable and non-biodegradable
wastes, minimises the use of plastics,
takes appropriate steps to promote
sustainable management of resources
in day-to-day life, advocates use of
fuels which produce less pollutants,
uses energy efficient electric devices,
uses fossil fuels judiciously, etc.
Suggested Pedagogical Processes in an Inclusive Setup
The curriculum in a classroom is same for everyone. This means
all students can actively participate in the classroom. There can
be some students who may face learning difficulties including
language, visual-spatial, or mixed processing problems. They
may require additional teaching support and some adaptation
in the curriculum. By considering the specific requirements of
children with special needs, a few pedagogical processes for the
teachers are suggested:

122
Learning Outcomes at the Secondary Stage
y Use multisensory approach for integrating information from
auditory, olfactory, tactile as well as visual sources.
y Provide learning experiences through touching objects,
materials, organisms, models, etc., to experience size,
shape, texture, pattern, and changes.
y Use embossed line diagrams for explaining texts, pictures,
graphs and flow charts, etc.
y Use direct sensory experiences for developing concepts like
temperature, volume, etc.
y Give opportunities to work with peers during experiments.
Rotating partners for the entire class would be a good
strategy.
y Allow students to record classroom presentation and
lectures or the text in audio format.
y Label the pictures within the text, whenever possible. This
can be done by the students as an activity.
y Relate the projects and experiments to real life experiences.
y Encourage group task and peer assistance for project and
experiment work.
y Give the project and experiment in fewer steps and sequence
the steps through visual cues. Display the examples
of completed projects and experiments in classroom or
laboratory for better understanding.
y Consider alternative or less difficult activities and exercises
for the students, with same or similar learning objectives.
y Write all homework or assignments and laboratory
procedural changes on the chalkboard.
y Give the student time to finish a step in an experiment and
wait until the student indicates that she/he is ready for
further work.
y Topics can be taught through class projects, experiments,
examples, etc. Activities can be conducted through
multisensory modes before explaining any theory and
concept.
y Peer support can be used wherever a figure or table has to
be drawn. Peer partner can draw with a carbon paper (for
copying).
y Highlight and underline the key concepts.
y Provide extra time to complete an experiment and understand
a concept.
y Always provide proper guidelines to arrange the task in a
planned way. Make use of visual aids, graphic organisers
and explain the steps of experiments and assignment
repetitively till the child learns.
y Sequence maps with visual cues can be provided to the
students to understand the sequence of events.

Class 10 Biological Science Textbook NCERT

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Class 10 Biological Science Textbook NCERT

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