Section B (Q Nos. 6-12 are of 2 marks each)
Question 6: Write the ploidy and number of chromosomes in human (a) meiocytes, and (b) gametes.
Answer:
(a) (meiocytes) 2n, 46.
(b) (Gametes) n, 23.
Question 7: What is aneuploidy? Name a chromosomal disorder in humans caused due to (a) gain of an autosome, and (b) loss of a sex chromosome in females.
Answer:
Failure of segregation of chromatids (during cell division), resulting in gain or loss of a chromosome (s).
(a) (Gain of an autosome) β Downβs syndrome.
(b) (Loss of a sex chromosome) β Turnerβs syndrome.
Question 8: State a functional difference between the following codons:
(a) AUG and UAA
(b) Specific and Degenerate
Answer:
a) AUG β Start codon / codes for Methionine / Met, UAA- Stop / codon / Nonsense Codon/ Does not code for any amino acid / Terminator Codon / Ochre.
b) Specific β one codon codes for one amino acid.
Degenerate β one amino acid coded by more than one codon.
Question 9: (a) Identify any two marsupials from the list given below:
- (i) Lemur
- (ii) Spotted cuscus
- (iii) Flying phalanger
- (iv) Bobcat
- (v) Tasmanian wolf
- (vi) Mole
(b) βAustralian marsupials exhibit adaptive radiation.ββ Justify the statement.
Answer:
a. ii) Spotted cuscus, iii) Flying phalanger, and v) Tasmanian wolf.
b. Australian marsupials each differ from the other evolved from an ancestral stock, all within the Australian island continent.
Question 10: Name the type of immunity the mother provides the newborn baby. How does it happen?
Answer:
Passive immunity.
Colostrum has (abundant) antibodies / IgA present
Question 11: Name the two primary lymphoid organs. State the importance of T-lymphocytes.
Answer:
Thymus, Bone marrow .
Functions: helps B-cells in production of antibodies, mediate CMI, responsible for graft rejection (any one).
Question 12: How are malignant tumors different from benign tumors? Why are some patients treated with Ξ± β interferons?
Answer:
Benign tumors remain confined to their original location/ do not spread to other part of the body / cause little damage / no metastasis, malignant tumors proliferate and spread to other body parts / is more harmful / cause serious damage/ causes metastasis.
Biological response modifiers / activate immune system to destroy tumor.
OR
Name the hormone with which a cow is administered using MOET technology. State the function of this hormone.
Answer:
Follicular Stimulating Hormone like / FSH like, to induce follicular maturation / super ovulation/production of 6-8 eggs.
Previous Year Question Paper for CBSE Class 12 Biology β 2020
CBSE Class 12 Biology Previous Year Question Paper helps you to understand the level of questions asked in the previous exams, along with the changes in pattern. Practicing the previous yearβs question paper for CBSE Class 12 Biology enhances time-management skills while appearing in the board examination. It makes you understand the importance of different topics that have been asked previously.
Previous yearβs CBSE Class 12 Biology Question Papers will boost your confidence level to appear in the examination with proper knowledge of different topics that are going to be asked. It enhances the understanding of the topic and acts as a checkpoint to see the level of preparation that you have done. CBSE Class 12 Biology Question Papers 2020 is available here.