CHENNAI SAHODAYA SCHOOLS COMPLEX

COMMON EXAMINATION

Class-12

(BIOLOGY – 044/2)

Maximum Marks: 70 Time allowed: 3 hours

1. C (1)

2. D (1)

3. B (1)

4. C (1)

5. A (1)

6. B (1)

7. C (1)

8. C (1)

9. A (1)

10. A (1)

11. C (1)

12. D (1)

13. A (1)

14. A (1)

15. A (1)

16. D (1)

SECTION – B

17 A- Chasmogamous flower B- Cleistogamous flower (1) (2)

Cleistogamous flowers – they have unexposed anther and stigma and therefore always
show self-pollination and assured seed set. (1)

(or)

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Apomictic seeds are produced without fertilization. (1)

To maintain hybrid characters (year after year in a desired plant) and to avoid buying
hybrid seeds every year (expensive seeds) farmers prefer using apomictic seeds. (1)

18. i- Passive immunity, ii- active immunity iii- Passive immunity iv- passive 4 X ½=2 (2)

19. Exo nuclease acts on the free ends of linear DNA molecule. Therefore, instead of producing (2)
DNA fragments with sticky ends, it will shorten or completely degrade the DNA fragment
containing the gene of interest, and the circular plasmid (vector) will not get cut as it lacks
free ends.

20. i - Nucleosome (½) (2)

ii- Packaging of chromosome (1)
iii- Histone protein (½)

21. i- It represents the number of tertiary consumers. (1) (2)

ii- PP- producers, for example, plant SC – secondary consumer, for example- cat (1)

SECTION – C

22. (a) The illustration represents adaptive radiation. (1) (3)

The process of evolution of different species in a given geographical area starting from a
point and radiating to other area of geography (habitats) is called adaptive radiation. (1)

(b) Convergent evolution (1)

(or)

(i) According to hardy – weinberg principle, total genes and their alleles in a population are
gene pool remains constant. This is called genetic equilibrium. Sum total of all the
allelic frequencies is P2 + 2pq + q2 = 1 (1)

(ii) Factors that affect Hardy-Weinberg equilibrium:

(i) Gene migration or gene flow

(ii) Genetic drift any two (2)
(iii) Mutation
(iv) Genetic recombination

23. Bioactive Molecule Medicinal Value (3)

Produced

(i) Streptococcus Streptokinase Removes clot from the blood vessels

(ii) Monascus Statin Inhibits enzymes responsible for

purpureus synthesis of cholesterol. So is used as

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cholesterol lowering agent.

(iii) Trichoderma Cyclosporin A Immunosuppressive agents used in

polysporum organ transplantion.

24. (a) Small round head / furrowed tongue / partially open mouth / mental development (3)
retarded (any one)

(b) Both

(c) Klinefelter’s syndrome

(d) Male

(e) Lack of secondary sexual charaters.

(f) Female 6x½=3

25. (a) Cells are treated with specific concentration of a divalent cation such as calcium to (3)
increase pore size in cell wall. The cells are incubated with recombinant DNA on ice,
following by placing them briefly at 40’C and then putted back on ice. This is called heat
shock treatment. (1)

(b) The DNA of bacteria or virus is modified with the desirable gene and introduced into
the plants or animals to get the desirable products. (1)

(c) Bacterial cell is treated with enzymes lysozyme.

Fungal cell is treated with chitinase. (1)

26. Curve ‘a’ is exponential growth curve. When the resources (food + space) are unlimited, (3)
this type of growth curve appears. (1)

Curve ‘b’ is logistic growth curve. When the resources become limited at certain point of
time, this type of growth curve appears. (1)

r = intrinsic rate of natural increase

K = carrying capacity (1)

27. Bt cotton contains inactive toxins protein or protoxin. These are insecticidal proteins in the (3)
form of crystal protein. Once the insect ingests its, the inactive protoxin is converted into
active form due to alkaline pH in the gut, which solubilise the crystals. The activated toxins
bind to the surface of midgut epithelial cells, thus creating pores which causes cell swelling
and lysis, eventually leading to the death of the insect pest.

28. Ramsar convention is an international treaty for the conservation and utilization of (3)

wetlands, recognizing the fundamental ecological functions of wetlands and their

economic, cultural, scientific and recreational value.

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Ramsar conversation. It was named after the city Ramsar in Iran. (1)

Ashtamudi wetland (Kerela), Bhitarkanika Manaroues (Orissa), Bhojcutland

(Madhya Pradesh), Chandra Taal (Himachal Pradesh) etc. (any one / any other
relevant answer) (1/2)

"Three pillars" of the convention:

Ensuring the conservation and wise use of wetlands

Including as for a possible the wise use of all wetlands in national environment

planning

Consulting with other parties about the implementation the convention,

especially

in regard to frameboundry wetland, shared water system and shared species (1½)

SECTION – D

29. (a) X –Temperate - 1 (4)

Y- Tropical -1

b) Y(Tropical) - 1
c) Amazonian forest -1
d) B
e) Birds species varies in different location
Colombia (equater) 1400, New York – 105 (41⸰N) , Green land – 56 (71⸰N)

30. (i) B (4)

(ii) C
(iii) D
(iv) C

(v) A

SECTION – E

31. a) High levels of progesterone and estrogens during pregnancy suppresses the (5)
gonodotrophins which are required for the development of new follicles. Therefore a
new cycle cannot be inititated (2)

b) Gametogenesis insemination Fertilization implantation Gestation

Parturation (1)

c) HCG – Human chorionic gonadotrophins

HPL – Human Placental lactogen

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Placenta (2)

(or)

 Rapid release of luteinising hormone ruptures Graafian follicle and release ovum
(ovulation). (1)
 Corpus luteum secretes large amount of progesterone hormone that is essential for
maintenance of the endometrium required for implantation of blastocyst leading to
pregnancy. (1)
 Placenta produces several hormones like human chorionic gonadotropin (hCG), human
placental lactogen (hPL). Relaxin is also produced during later phase of pregnancy.
Level of other hormones like estrogens , progestogens, cortisol, prolactin and throxine
also increases which is essential for supporting foetal growth, metabolic changes in
mother and maintenance of pregnancy. (1)
 Parturition signals originate from the fully developed foetus and the placenta induce
mild uterine contractions which triggers release of oxytocin from pituitary. Oxytocin
acts on the uterine muscle causing stronger uterine contractions. (1)
 Mammary glands undergo differentiation during pregnancy and produce milk by
lactation. Secretion and storage of milk occurs under influence of hormone. Prolactin
secreted by anterior lobe of pituitary. Ejection of milk is stimulated by oxytocin from
posterior lobe of pituitary. (1)

32. i- Francis Crick (1) (5)

ii- a- Replication, b- Transcription c- Translation d- Reverse Transcription (2)
iii- a- DNA dependent DNA polymerase b- RNA dependent RNA polymerase d-Reverse
transcriptase ( )

iv- In the life cycle of HIV. ( )

(or)

i. inducer
ii. Operator (o)
iii. Permease (y) (3)

(2)

33. Condition – I

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Condition – II

Phenotype 50% homozygous : 50% heterozygous F1 ratio = 1 : 1 (1/2)

(or)

End of the paper

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