bio 12th 25.pdf. Paper bio 12 the class

Paper

1. Roll No :
Date :
Name of School :
Name of Assessment :
Subject :
Class :
Time :
Marks: 92
1The number of meiotic divisions, required to produce 400 seeds in a pea
plant, is
(a) 100 (b) 200
(c) 400 (d) 500
Ans : (d)
1
2Choose the option that gives the correct number of pollen grains that will be
formed after 325 microspore mother cells undergo microsporogenesis.
(a)325
(b) 650
(c) 1300
(d) 975
Ans :
(c) Each microspore mother cells forms four microspores/pollen grains after
meiosis.
1
3When the pollen of a flower is transferred to the stigma of another flower on
the same plant, the process is known as
(a) autogamy (b) geitonogamy (c) xenogamy (d) cleistogamy
Ans : (b)
1
4Androgens are synthesised and secreted by
(a)Sertoli cells
(b)prostate gland
(c)Leydig cells
(d)seminal vesicles
Ans : (c)
1
5Which of the following hormones prepares the uterus for implantation?
(a)Progesterone
(b)FSH
(c)Estrogen
(d)LH
Ans : (a)
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2. 6Medical termination of pregnancy (MTP) is considered safe up to _________
weeks of pregnancy.
(a)Six
(b)Eight
(c)Twelve
(d)Sixteen
Ans : (c)
1
7Which of the following pairs are the sexually-transmitted diseases (STDs)
that can be cured?
(a) Syphilis and AIDS
(b)Gonorrhoea and genital herpes
(c)AIDS and hepatitis-B
(d)Syphilis and gonorrhoea
Ans : (d)
1
8A female undergoing IVF treatment has blocked fallopian tubes. The
technique by which the embryo with more than 8 blastomeres will be
transferred into the female for further development is
[CBSE Sample Paper 2022]
(a) ZIFT
(b) GIFT
(c) IUT
(d) AI
Ans : (c)
1
9Diacetylmorphine is commonly known as
(a) cocaine
(b) hashish
(c) ganja
(d) heroin
Ans : (d)
1
10 Morphine is extracted from
(a) Atropa belladona
(b) Papaver somniferum
(c) Erythroxylum coca
(d) Cannabis sativa
Ans : (b)
1

3. 11The vitamin whose content increases following the conversion of milk into
curd by lactic acid bacteria is [NCERT Exemplar Problems]
(a) vitamin C (b) vitamin D
(c) vitamin B (d) vitamin E.
Ans : (c)
1
12Identify the fungus that ripens the famous ‘Roquefort cheese.’
(a) Saccharomyces cerevisiae
(b) propionibacterium sharmanii
(c) monascus purpureus
(d) penicillium notatum
Ans : (d)
1
13Mycorrhiza is an example of
(a) ectoparasitism (b) mutualism
(c) endoparasitism (d) predation
Ans : (b)
1
14The interspecific interaction in which one partner is benefitted and the other
is unaffected (neutral), is called
(a) amensalism (b) mutualism
(c) competition (d) commensalism
Ans : (d)
1
15Swathi was growing a bacterial colony in a culture flask under ideal
laboratory conditions where the resources are replenished. Which of the
following equations will represent the growth in this case? (Where
population size is N, birth rate is b, death rate is d, unit time period is t, and
carrying capacity is K). 
(a) dN/dt = KN
(b) dN/dt = rN
(c) dN/dt = rN(K – N/K)
(d) dN/dt = rN(K + N/K)
Ans : (b)
1
16In the equation GPP – R = NPP, R represents.
(a) radiant energy
(b) retardation factor
(c) environmental factor
(d) respiratory losses.
Ans : (d)
1
12

4. 17What are false fruits? Give two examples.
Ans :
If any part of the flower other than the ovary becomes a part of the fruit, the
fruit is said to be a false fruit, e.g. Apple, pear, strawberry.
2
18What are parthenocarpic fruits? Mention one characteristic feature of such
fruits
Ans :
– The fruits that are formed without fertilisation of the ovary, are called
parthenocarpic fruits. – THey are generally seedless or seeds are not viable.
2
19Given below is an enlarged view of one microsporangium of a mature
anther.
(i) Name ‘a’, ‘b’ and ‘c’ wall layers.
(ii) Mention the characteristics and function of the cells forming the wall
layer ‘c’.
Ans :
(i) (a) Endothecium (b) Middle layers (c) Tapetum
(ii) – The cells of tapetum possess
(a) dense cytoplasm and (b) more than one nucleus
– They nourish the developing pollen grains.
3
20Read the following passage and answer the questions that follow:
The pollen grains represent the partially developed male gametophyte of
angiosperms. They show an amazing variety of architecture, when observed
under a microscope. They are generally spherical and measure about 25-50
micrometres in diameter. Each pollen grain has a prominent two-layered
wall. Pollen grains are well-preserved as fossils. 
(a)How many pollen grains are formed from a pollen mother cell?
(b)What are germ pores in a pollen grain?
(c)How many cells are present in a pollen grain, at the time of its release
from the anther? Name them.
Or
4

5. (c)Refer to the figure given and match the parts (with their names) labelled
with their characteristics mentioned.
1. It is made of a highly-resistant organic material.
2. It is spindle-shaped in outline and has dense cytoplasm with a
prominent nucleus.
3. It has vacuolated cytoplasm and an irregularly-shaped nucleus.
4. It is made of pectin and cellulose.
Ans : (a)Four.
(b)Germ pores are those places on the exine of a pollen grain, where
sporopollenin is thin or absent and gives the appearance of an aperture.
(c)–Pollen grains may be 2-celled, with a vegetative cell and a
generative cell.
–Pollen grains may be 3-celled with a vegetative cell and two male
gametes.
Or
(c)1. D, Exine
2. A, Generative cell
3. B, Vegetative cell
4. C, Intine
21Study the diagram given below showing the modes of pollination. Answer
the questions that follow:
(a) The given diagram shows three methods of pollen transfer in plants.
What are the technical terms used for pollen transfer methods ‘1’, ‘2’ and
‘3’?
5

6. (b) How do the following plants achieve pollination successfully?
(i) Water lily
(ii) Vallisneria
(c) Flowering plants have developed many devices to avoid inbreeding
depression. Explain one hereditary and one physiological device which
helps plants to achieve this target.
Ans : (a) ‘1’ – Autogamy‘2’ – Geitonogamy‘3’ – Xenogamy
(b) (i) Water lily is pollinated by insects, (like terrestrial plants), as the
flowers emerge above the water level.
(ii) Vallisneria shows true hydrophily and is pollinated by water.
(c) Outbreeding devices to prevent inbreeding depression
(i) Self-incompatibility is the genetic mechanism that prevents self-pollen
(pollen from the same flower as the pistil or a different flower on the same
plant) from fertilising the ovule by inhibiting pollen germination or retarding
the growth of the pollen tube.
(ii) Dioecy is the phenomenon in which male and female flowers are produced on different
plantsand the plants are described as dioecious; thisprevents both
autogamy and geitonogamy.
22(a) Define pollination.
(b) Differentiate between: Autogamy, Geitonogamy and Xenogamy, with an
example of each.
Ans :
(a) Pollination refers to the transfer of pollen grains from the anthers to the
stigma of a flower.
5
23The diagram given below shows a developmental stage of human embryo.
Answer the following questions with reference to it:
2

7. (a) Identify and name the human embryonic stage shown.
(b) Mention its exact location in the normal pregnancy of a woman.
(c) Write one function of each of the two parts labelled ‘X’ and ‘Y’.
Ans : (a) It is a blastocyst
(b) It becomes embedded in the endometrium of the uterus.
(c) – X-Trophoblast; it forms the foetal part of placenta.
– Y-Inner cells mass becomes differentiated as the embryo.
24Identify A, B, C and D with reference to gametogenesis in humans, in the
flow chart given below:
Ans :
A – Leydig cells
B – Sertoli cells
C – Spermatogenesis
D – Spermiogenesis.
2
25Study the figure given:
(i) Name the structure of which the given diagram is a part of.
(ii) Pick out and name the motile cells.
(iii) Name ‘b’ and ‘c’ cells. What is the difference between them with
reference to the number of chromosomes?
3

8. Ans : (i) Seminiferous tubule.(ii) e – spermatozoa
(iii) b – primary spermatocyte
c – secondary spermatocyte – Primary spermatocyte is diploid (2n = 46)
while the secondary spermatocyte is haploid (n = 23).
26Read the following passage and answer the questions that follow:
Condoms are the barriers made of thin rubber or latex sheath that are used
to cover the penis in the males and the vagina and cervix in females during
coitus.
Observe the diagram given below and answer the questions that follow: 
(a) What is the principle of birth control in the barrier methods?
(b)Identify the male and female contraceptive devices, A and B represent,
respectively.
(c)Mention two advantages (other than contraception) that are provided by
A to the user.
Or
(c)How does B function as a contraceptive in a human female? Name two
reusable berries used by females.
Ans :
(a)In the barrier methods, the ovum and sperms are prevented from
physically meeting, with the help of the barriers.
(b)A.Condom for males.
B. Condom for females.
(c)(i)They protect the user from contracting sexually-transmitted
diseases.
(ii)Since they are self-inserted, they give privacy to the user.
Or
(c)– It covers the cervix and prevents the entry of sperms  through the
cervix and thereby prevent fertilisation.
– Diaphragms, cervical caps, vaults.(any two)
4
27Expand the following
(i) ICSI,
(ii) GIFT,
5

9. (iii) ZIFT
(iv) IUT
(v) IUI.
Ans :
(i) ICSI: Intra-cytoplasmic sperm injection
(ii) GIFT: Gamete intra-fallopian transfer
(iii) ZIFT: Zygote intra-fallopian transfer
(iv) IUT: Intra-uterine transfer
(v) IUI: Intra-uterine insemination.
28Explain the barrier methods of Birth control.
Ans :
– In the barrier methods, the ovum and sperms are prevented from
physically meeting with the help of barriers.
– These barriers are available for both males and females.
– Condoms are the barriers made of rubber or latex sheath that are used to
cover the penis in males and the vagina and cervix in females during coitus
to prevent the semen from entering the female genital tract; both male and
female condoms are disposable.
– Diaphragms, vaults and cervical caps are also the barriers used by
females; they are reusable.
3
29Differentiate between benign and malignant tumours.
Ans :
2
30Study a part of the life cycle of malarial parasite given below. Answer the
questions that follow:
3

10. (a) Mention the roles of 'A' in the life cycle of the malarial parasite.
(b) Name the event 'C' and the organ where this event occurs.
(c) Identify the organ 'B' and name the cells being released from it.
Ans :
(a) A part of the life cycle of the parasite occurs in the body of female
Anopheles mosquito; these mosquitoes act as vectors and transmit the
disease from patients to healthy individuals.
(b) Fertilisation; it occurs in the intestinal wall of mosquito.
(c) Salivary gland. Sporozoites are the cells released from it.
31Name the first antibiotic discovered and by whom?
Ans : – Penicillin is the first antibiotic.
– It was discovered by Alexander Fleming.
2
32Name the enzyme produced by Streptococcus bacterium. Explain its
importance in medical sciences.
Ans :
Streptokinase is the enzyme produced by Streptococcus.
– It is used as a clot-buster to remove clots from the blood vessels of
patients who have suffered myocardial infarction.
2
33
Observe the schematic representation given above and answer the
following questions:
(a) Identify A and B
2

11. (b) Calculate the growth rate of bacteria in a curd sample, where 1 million
bacteria increased to two million, within a period of one hour.
Ans : (a) – A - Mortality – B - Natality
(b) The growth rate of bacteria is 1 million/hour
34Study the three different age pyramids for human population given below and
answer the questions that follow:
(a) Write the names given to each of these age pyramids.
(b) Mention the one which is ideal for human population and why?
Ans :
(a) A – Expanding, B – Stable, C – Declining.
(b) Stable population is preferred. It is helpful for planning any welfare
activity.
3
35We have been concerned about the unbridled human population growth and
the problems arising out of it in our country. Hence, we are curious to know
the growth patterns of different animal populations in nature. Study the
population growth curves shown in the given figure and answer the
questions that follow:
(a) Identify the type of growth curves ‘A’ and ‘B’.
(b) What does the dotted line in the graph indicate? Define the same.
(c) Name the four different phases in the growth curve ‘B’.
Or
(c) Which one of the above two curves is more realistic? Give reason.
Ans : (a) – A – Exponential growth curve – B – Logistic growth curve
(b) – The dotted line represents the carrying capacity.
– Carrying capacity refers to the maximum number of individuals of a
population that a given environment can sustain with its resources.
(c) Lag phase, phase of acceleration, phase of deceleration and asymptote.
4

12. Or
(c) – Curve A appears when resources are unlimited and curve B appears
when resources are limited in the habitat.
– Logistic growth curve is realistic; since resources are finite and can
become limiting sooner on later, exponential growth cannot continue; hence,
logistic growth curve is more realistic.
36Justify the statement, ‘Pyramid of energy is always upright and can never
be inverted’.
Ans : Pyramid of energy is always upright because
– only 10 per cent of energy is passed on from one trophic level to the next
higher trophic level.
– during the flow of energy from one trophic level to the next, some energy
is always lost as heat at each step.
2
37(a) What is an ecological pyramid? Compare the pyramids of energy,
biomass and numbers.
(b) Write any two limitations of ecological pyramids.
Ans :
(a) The graphic representation of the number, food/energy relationships or
biomass of the different trophic levels of a food chain at a given time, is
called an ecological pyramid.
Comparison:
Pyramid of EnergyPyramid of BiomassPyramid of Numbers
– It is the graphic
representation of
the amount of
energy present at
each trophic level
of a food chain, at a
given time.
– It is always
upright, and
never inverted,
because the
amount of energy
present in
producers is more
than that in
consumers.
– It is the graphic
representation of the
biomass/living
organic matter present
at each trophic level of
a food chain, at a
given time.
– It may be upright as
in a
grassland ecosystem
or inverted as in sea
(aquatic) ecosystem.
– It is the graphic
representation of
the number of
organisms present
at each trophic level
of a food chain, at a
given time.
– It may be upright
as in a forest or
grassland
ecosystem
or inverted as in a
tree ecosystem.
(b) Limitations of ecological pyramids:
5

13. (i) They do not take into account the same species belonging to two or more
trophic levels.
(ii) It assumes a simple food chain, whereas in nature it does not exist.
(iii) Saprophytes/decomposers are not given any place in ecological
pyramids. (any two)
38There are many animals, which have become extinct in the wild, but
continue to be maintained in zoological parks.
(a) What type of biodiversity conservation is observed in this case?
(b) Explain any other two ways which help in this type of conservation.
Ans :
(a) Ex situ conservation.
(b) (i) Cryopreservation
– Gametes of threatened species of animals are preserved in viable and
fertile conditions for long periods in this method.
(ii) In vitro fertilisation, using the gametes stored by cryopreservation.
3
39Given below is an equation describing the Species- Area relationship
between species richness and area for a wide variety of taxa as angiosperm
plants, birds, bats, etc.
(a) Give a graphical representation of the given equation showing Species-
Area relationship.
(b) What does ‘S’ represent in the given equation?
(c) What is the value of ‘Z’ (regression coefficient) for frugivorous birds and
mammals in the tropical forests of different continents?
Ans : (b) ‘S’ represents species-richness
(c) Z value is 1.15 for frugivorous birds and mammals.
3

14. 40(a) Taking one example each of habitat loss and fragmentation, explain how
the two are responsible for biodiversity loss.
(b) Explain two different ways of biodiversity conservation.
Ans :
(a) Habitat loss and fragmentation
– It is the primary cause for extinction.
– The tropical rain forests initially covered 14% of the land surface of the
earth, but now they cover only 6% of land area.
– Total loss of a habitat deprives many animals and plants of their homes
and they face extinction.
– When a large habitat becomes fragmented, animals requiring large
territories and those with certain migratory habits start decreasing.
(b) Refer to answer 52
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