Project on Modification of roots

This project is on biology.Topic is Modification of roots.It is for class 11 students

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CERTIFICATE

his is to certify that SUMAN PAL of class-XI, JAWAHAR NAVOD AYA
VIDYALAYA-II with Roll No. 24 has satisfactorily completed this
Biology Project on MODIFICATION OF ROOT in partial fulfillment of the
requirements as prescribed by CBSE in the year 2017-18.





Signature of the Subject Teacher Signature of Principal











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ACKNOWLEDGEMENT
wish to express my deep gratitude and sincere thanks to the
Principal, Shree Amal Karmakar, Jawahar Navodaya
Vidyalaya-II, South 24 Parganas for his encouragement and for
all the facilities that he provided for this project work. I
sincerely appreciate this magnanimity by taking me into his
fold for which I shall remain indebted to him. I
extend my hearty thanks to Mrs. Laxmi Rai(PGT, Biology), who
guided me to the successful completion of this project. I take
this opportunity to express my deep sense of gratitude for her
invaluable guidance, constant encouragement, immense
motivation, which has sustained my efforts at all the stages of
this project work….
I can’t forgot to offer my sincere thanks to parents and
also to my classmates who helped me to carry out this project
work successful and for their valuable advice and supervision
which I received from them time to time.


Signature of Student



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Index
Sl
no.
Contents Page no. Sign of
Teacher
1.
Introduction 4

2.
theory 4-5
3.
Tap root system 5-8
4.
Adventitious root system 8-16
5.
Conclusion 17
6.
bibliography 18

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Sign of Principal




Objective of the project
To study the modification of root
INTRODUCTION
oot is the underground part of plant. It develops from the radical of
germinating seed. Its primary function is absorption of water and
minerals. It also helps in anchoring of plant to the soil. On the basis of their
place of formation, root system is mainly two types- i)Tap root
system(develops from radicale of germinating seed) and ii) Adventitious root
system(produced from any other part of thr plant except the radicle).
When dissected, the arrangement of the cells in a root is root hair,
epidermis, epiblem, cortex, endodermis, pericycle and, lastly, the vascular
tissue in the centre of a root to transport the water absorbed by the root to
other places of the plant. Perhaps the most striking characteristic of roots
(that makes it distinguishable from other plant organs such as stem-branches
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and leaves) is that, roots have an endogenous origin, i.e. it originates and
develops from an inner layer of the mother axis (Such as Pericycle). Whereas
Stem-branching and leaves (those develop as buds) are exogenous, i.e. start
to develop from the cortex, an outer layer.
THEORY
oots are modified into different forms to perform specific functions other
than their normal functions. Modification in roots is found in both tap
root system and adventitious root system.
Modification in root occurs when there occurs a permanent change in the
structure of the root system. This change in structure of the tap root or the
adventitious root system is for carry out certain specific functions additional
to anchorage and absorption. The change in the structure of the roots is for
adaptation to their surrounding environment. In this way the tap root and
adventitious root also get modified into various forms to perform several
other modified functions. The various forms of modification are described
below:


MODIFICATION OF ROOT

1. Tap root system: In addition to their normal function, tap roots
perform several other modified functions also.
These modified forms of tap roots are as follows:
a) Fleshy tap roots:
These roots modify to store food materials. The primary root becomes
swollen due to the presence of stored food.
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Depending upon the shape, the storage or fleshy tap roots can be classified
into following types
 Conical tap root: These are conical in shape , i.e. widest at top, tapering
smoothly towards the bootom, e.g. Carrot (Daucus carota).


Fig. 1: Carrot

 Fusiform tap root: The is broader in the middle and narrower at the
both ends giving spindle-shaped appearance, e.g. Radish (Raphanus
sativus).

Fig. 2: Radish

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 Napiform tap root: Such a root swells extraordinarily in the middle and
becomes abruptly narrower towards the apical region, e.g. Brassica
rapa (Shalzum) and Beta vulgaris (Chunkander).

Fig. 3: Napiform tap root

 Tuberous tap root: These are thick and fleshy tubers of indefinite and
irregular shape, e.g. roots of Mirabilis jalapa and Cassava.

b) Nodulated tap root:
The plants of Leguminosae family are characterized by the presence of
nodules on roots. These are called as nodulated or tuberculated roots.
Nodules on these roots bear N2-fixing bacteria, i.e. Rhizobium. Thus, these

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roots helps in N2-fixation, e.g. pea,gram,arhar,etc.

Fig. 4: Nodulated root
c) Respiratory roots:
These roots are found in plants growing in swampy/marshy areas. The
underground roots of such plants start growing up and become aerial
(negatively geotropic).These roots posses minute pores on tips. These help in
respiration and are called pneumathodes. Since these roots bring about
exchange of gases so, these are also called as pneumatophores or respiratory
roots, e.g. Avicennia, Rhizophora, etc. The pneumatophores of Rhizophora
are exceptional as the prop roots are non-hygroscopic.

Fig. 5: Respiratory root

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2. Adventitious root system:
These roots get modified to perform the following functions:
a) Storage of food:
Sometimes, the adventitious roots get swollen and become thick due to
storage of food. Depending upon their shape and place of swellings, these
roots can be classified into following categories
 Tuberous roots: These roots arise from internodes of stem, grow and
become fleshy and tuberous as a result of food storage. They do not
have a definite shape, e.g. Sweet Potato (Ipomoea batata).

Fig. 6: Sweet Potato
 Fasciculated roots: These roots are produced from or lower node of
stem forming a cluster, e.g. Dahlia.

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Fig. 7: Dahlia

 Moniliform roots: These roots are swollen at regular intervals giving a
bead like appearance of necklace, e.g. Momordica, Portulaca, etc.

Fig. 8: Moniliform roots
 Annulated roots: Formed by a number of swollen discs placed one
above the other. It looks like a series of ring-like outgrowths or
swellings, e.g. Cephaelis(Ipecac), Psychotria, etc.

Fig. 9: Ipecac

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 Palmate roots: These roots are branched such that they give the
appearance of the palm of human hand, e.g. Orchis, Aconitum, etc.

Fig. 10: Palmate roots

 Nodulose roots: These roots are swollen at their tips.Curcuma
amada(mango ginger), Curcuma domestica(termeric) and
Maranta(arrow-root), etc.

Fig. 11: Turmeric and Ginger

b) Mechanical support:
The adventitious roots modify into following types to provide mechanical
support:

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 Buttress roots: These roots radiate from the base of the tree (like
finger projections) to provide mechanical support, e.g. Ficus, Bombax,
Terminalia, Salmalia, etc.

Fig. 12: Buttress roots

 Stilt roots or Brace roots: These roots develop from the basal nodes of
the stem near soil. These provide mechanical support by fixing the
plant firmly in soil, e.g. Saccharam officinarum(sugercane), Zea
mays(maize), Pandanus tincotorious, etc.

Fig. 13: Maize and Sugercane

 Prop or Pillar roots: These roots develop from the large horizontal
aerial branches. These grow vertically downward penetrate the soil
and become thick. Thus, they give a piller-like appearance, e.g.
Banyan.

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Fig. 14: Banyan tree

 Contractile roots: These roots become thick, fleshy and contractile.
These remain associated with underground stems, e.g. Crocus.

Fig. 15: Corcus

 Climbing or Clinging roots: These roots arise from the nodes and help
the plant in climbing. These stick firmly to a support by secreting a
cementing gummy substance, e.g. Ficus pumila, betal, etc.

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Fig. 16:Climbing root

c) Vital or Physiological functions:
Roots modify into following types to perform vital functions
 Assimilatory or Photosynthetic roots: Adventitious roots of certain
plants develop chlorophyll and become green. These roots can carry
out photosynthesis, e.g. Trapa, Tinospora and Podostemons.



Fig. 17: Photosynthetic root

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 Parasitic or Haustorial roots: These roots are developed by the
parasitic plants. These roots penetrate host tissue for absorbing
nourishment, e.g. Cuscuta is a parasitic plant on plants like Duranta,
Acacia, etc.

Fig. 18: Parasitic root
 Epiphytic roots: The roots of the epiphytes hang in the air. These
absorb hygroscopic water present in the atmosphere by special tissue
called velamen, e.g. Vanda, Dendrobium, Orchids.

Fig. 19: Epiphytic roots

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 Reproductive roots: In some plants, roots help in vegetative
reproduction, e.g. parwal. In case of sweet potato the adventitious
buds act as reproductive roots thus giving rise to new plants.


Fig. 20: Reproductive root
 Floating roots: These roots are adventitious roots present in some
floating plants. These arise from nodes. These store air, become
inflated and spongy. Thus, they make a plant light by functioning as
floats, e.g. Jussiaea.

Fig. 21: Floating root

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.

Conclusion
Unseen and buried beneath the soil, plant roots perform functions that are
necessary to a plant's life. The roots collect water and nutrients for the plant and
secure it to the soil. Two basic types of root systems exist. One type is the
taproot, which grows vertically and has lateral branches. The other type has
fibrous, branching roots that make a network close to the soil surface. Some
plants have either a taproot or fibrous roots, and other plants combine the two
systems.
Plant roots absorb water through root hairs, which are tiny roots that extend
from the root's epidermis, or the outer layer of the root. Just one cell thick, they
absorb water and nutrients from the soil. Fibrous roots, with their thickly
branching system and more numerous roots, have more surface area and more
root hairs than taproot systems do to take in food and water. Corn (Zea mays) is
an example of an annual plant with a fibrous root system that harvests large

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quantities of water and nutrients from the soil, allowing it to grow over 6 feet
tall in a single growing season.
Both water and wind act to expose plant roots or destabilize plants. Fibrous root
systems help prevent soil erosion as they anchor plants to the top layers of soil.
Grasses are an example of a type of plant with densely fibrous root systems that
keep soil in place. Taproots anchor plants deeply, helping to prevent the wind
from blowing them over and stabilizing plants that grow in areas of shifting
soils such as beaches or sand dunes. Dandelions (Taraxacum officinale, USDA
zones 3 through 9), which are considered invasive in many areas, have a strong
taproot that holds the plant in place, making it difficult to remove the plant once
it is established.

Taproots are often modified for food storage. Examples are carrots (Daucus
carota) and sugar beet (Beta vulgaris). These annuals have the original, primary
taproot modified to store starches and sugars. The food reserves can be drawn
upon to ensure good development of a flower stalk and seeds. Perennial plants
with taproots such as dandelion use stored food to send up new leaves in the
spring. Plants with fibrous root systems usually don't have roots modified for
food storage. Other crops thought of as root crops, such as potato (Solanum
tuberosum), aren't roots, but modified underground stems called tubers.

Bibliography


 NCERT Biology class 11
 Arihant Exploring Biology (Vol.1)
 Google.co.in
 Wikipedia.org

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