PART B: ZOOLOGY (2018 March):
ANSWERS
1. Leydig cells (Interstitial cells).
2. (b) Saheli
3. (c) Exons
4. This statement is true.
Because male can produce two types of gametes (sperms) – one with X chromosome
and other with Y chromosome. Y chromosome is responsible for the male sex of
the baby. Female can produce only gametes (Egg) containing X chromosome. X
chromosome is responsible for female sex of the baby.
5. Natural methods: Periodic abstinence, Coitus
interruptus (withdrawal), Lactational amenorrhea.
Barrier methods: Condoms, diaphragms,
cervical caps, vaults.
6. (a) Negatively charged DNA is wrapped around positively charged histone
octamer to form nucleosome.
(b) Euchromatin:
Loosely packed and transcriptionally active region of chromatin.
Heterochromatin: Densely packed and inactive
region of chromatin.
7. (a) Incomplete dominance.
(b) It is an inheritance in which heterozygous
offspring shows intermediate character b/w two parental characteristics.
8. A= Homologous organs.
B= Divergent evolution.
C= Analogous organs.
D= Convergent evolution
9. Gene migration, Genetic drift, Mutation, Genetic recombination,
Natural selection.
10. Physical barriers: E.g. Skin.
Physiological barriers: E.g. Gastric HCl.
Cellular barriers: E.g. Neutrophils.
Cytokine barriers: E.g. Interferon.
11. A = Salmonella typhi
B = Common cold
C = Plasmodium falciparum
D = Filariasis (Elephantiasis)
12. Drop in academic performance and absence from school.
Lack of interest in personal hygiene.
Withdrawal and isolation.
Change in sleeping and eating habits.
Loss of interest in hobbies.
13. It is catalytic and hence reactive. It is single stranded and
has 2’-OH group in sugar. So RNA is less stable and mutate faster.
14. A= Aspergillus niger.
B= Bacterium
C= Cyclosporine A
D= Saccharomyces cerevisiae.
15. (a) S= Species richness, A= Area, Z= Slope of the line, C= Y-intercept.
(b) Alexander von Humboldt.
16. (a) The statement is true. Lactose switches on the lac operon
system inducing the action of structural genes.
(b) A= Repressor mRNA, B= b-galactosidase, C= Permease
D= Transacetylase.
17. (a) Gonorrhoea, syphilis, genital herpes, chlamydiasis etc.
(b) Avoid sex with unknown partners/multiple
partners.
Always use condoms during coitus.
18. (a) Mendelian disorders are the disorders caused by the alteration
or mutation in the single gene.
(b) Phenyl Ketonuria. It is due to mutation of a gene that codes for the enzyme phenyl alanine hydroxylase. As a result, phenylalanine accumulates and converts into phenyl pyruvic acid and other derivatives.