CBSE Class 12 Biology Answer Key 2024 and Question Papers, Download PDF All SETs

Board

Central Board of Secondary Education (CBSE)

Subject

Biology

Subject Code

044

Class 

12

Marks Distribution

Theory: 70

Practical: 30

Total No. of Units

5

Total No. of Chapters

13

Theory Exam Day

Tuesday

Theory Exam Date

March 19, 2024

Theory Exam Timings

10:30 a.m. to 1:30 p.m.

Exam analysis/Expert Review

Section

No. of Questions

Marks

Section A

16

16 x 1 = 16

Section B

5

5 x 2 = 10

Section C

7

7 X 3 = 21

Section D

2 Case Studies

2 x 4 = 8

Section E

3

3 x 5 = 15

Total

33

70

Download CBSE 12th Biology Question Paper 2024 PDF (All Sets)

SECTION A

Question 1) A single gene that controls the expression of more than one trait is said to show
(A) Multiple allelism
(C) Incomplete dominance
(B) Polygenic inheritance
(D) Pleiotropism

Answer: Pleiotropism

2. A person with trisomy of 21st chromosome shows
(i) Furrowed tongue
(ii) Characteristic palm crease
(iii) Rudimentary ovaries
(iv) Gynaecomastia
Select the correct option, from the choices given below:
(A) (ii) and (iv)
(C) (ii) and (iii)
(B) (i), (ii) and (iv)
(D) (i) and (ii)

Answer: (D) (i) and (ii)

3. Observe the schematic representation of assisted reproductive technology given below:

Identify the most appropriate technique depicted in the above diagram.
(A) IUT
(B) IUI

(C) ICSI
(D) ZIFT

Answer: (C) ICSI (Intracytoplasmic sperm injection)

4. Interferons are proteins secreted by
(A) RBC
(C) Bacteria infected cell
(B) WBC
(D) Virus infected cell

Answer: (D) Virus infected cell

5.During biological treatment of sewage, the masses of bacteria held together by fungal filaments to form mesh like structures are called

(A) primary sludge

(C) activated sludge

(B) flocs

(D) anaerobic sludge

Answer: (B) flocs

6.Which one of the following statements is correct in the context of observing DNA separation by agarose gel electrophoresis?

(A) DNA can be seen in visible light.

(B) DNA can be seen without staining in visible light.

(C) Ethidium bromide stained DNA can be seen in visible light

(D) Ethidium bromide stained DNA can be seen under UV light.

Answer: (D) Ethidium bromide stained DNA can be seen under UV light.

7. A phenomenon where a male insect mistakenly identified the patterns of aorchid flower as the female insect partner, and tries to copulate and thereby pollinates the flower is said to be:

(A) Pseudocopulation

(C) Pseudoparthenocarpy

(B) Pseudopollination

(D) Pseudofertilisation

Answer: (A) Pseudocopulation

8.Identify the correct labellings in the figure of a fertilised embryo sac of an angiosperm given below:

(A) A-zygote, B-degenerating synergids, C-degenerating antipodals, D-PEN

(B) A-degenerating synergids, B-zygote, C-PEN, D-degenerating antipodals

(C) A-degenerating antipodals, B-PEN, C-degenerating synergids, D-zygote

(D) A-degenerating synergids, B-zygote, C-degenerating antipodals, D-PEN

Answer: (B) A-degenerating synergids, B-zygote, C-PEN, D-degenerating antipodals

 9.Study the pedigree chart of a family showing the inheritance pattern of a certain disorder. Select the option that correctly identifies the nature of the trait depicted in the pedigree chart.

(A) Dominant X-linked

(B) Recessive X-linked

(C) Autosomal dominant

(D) Autosomal recessive

Answer: (B) Recessive X-linked

 10. Match the following genes of the lac operon listed in column 'A' with their respective products listed in column 'B':

Select the correct option:

Options:

         a   b   c    d

(A) (i) (iii) (ii) (iv)

(B) (iii) (i) (ii) (iv)

(C) (iii) (i) (iv) (ii)

(D) (iii) (iv) (i) (ii)

Answer: (C) (iii) (i) (iv) (ii)

11. If both the parents are carriers for thalassaemia, the chances of an afflicted child to be born to them is:

(A) 25%

(B) 50%

(C) 75%

(D) 100%

Answer: (A) 25%

12. If the sequence of nitrogen bases of the coding strand in a transcription unit is 5'-ATGAATG-3', the sequence of bases in its RNA transcript would be

(A) 5'-AUGAAUG-3'

(B) 5'-UACUUAC-3'

(C) 5'-CAUUCAU-3'

(D) 5'-GUAAGUA-3'

Answer: (A) 5'-AUGAAUG-3'

13. Assertion (A): AIDS is a syndrome caused by HIV.

Reason (R): HIV is a virus that damages the immune system with DNA as its genetic material.

Answer: (C) (A) is true, but (R) is false.

 14. Assertion (A): In molecular diagnosis, single stranded DNA or RNA tagged with radioactive molecule is called a probe.

Reason (R): A probe always searches and hybridises with its complementary DNA in a clone of cells.

Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).

 15. Assertion (A): In birds the sex of the offspring is determined by males.
Reason (R): Males are homogametic while females are heterogametic.

Answer: (D) (A) is false, but (R) is true.

16. Assertion (A): Communities that comprise of more species tend to be more stable.

Reason (R): A higher number of species results in less year to year variation in total biomass.

Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).

SECTION B

17. (a) "Farmers prefer apomictic seeds to hybrid seeds." Justify giving two reasons.

Answer: Farmers favor apomictic seeds because they're essentially maternal clones of the high-yielding hybrid parent. This eliminates the need to buy expensive new hybrid seeds every year, saving money. Additionally, apomictic seeds ensure consistent crop quality since  the new plants are genetically identical and they inherit the desired traits of the parent plant. It also remove the need of pollination and then fertilization.

OR

(b) Mention one advantage and one disadvantage of amniocentesis.

Answer: Advantage: Amniocentesis helps in identifying genetic defects in the foetus. 

Disadvantage: Amniocentesis also used for sex determination of the unborn child that increases the cases of  female foeticide.

18.

5'-G↓AATTC-3'

3'-CTTAA↑ G-5'

(a) Name the restriction enzyme that recognises the given specific sequence of bases. What are such sequence of bases referred to as?

Answer: Restriction enzyme: EcoRI. Palindromic sequences.

(b) What are the arrows in the given figure indicating? Write the result obtained thereafter.

Answer: The arrows indicate the restriction sites for EcoRI. 

Result:

5'-G                 AATTC-3'

3'-CTTAA                G-5'

19. Observe the population growth curve and answer the questions given below:

(a) State the conditions under which growth curve 'A' and growth curve 'B' plotted in the graph are possible.

Answer: Growth A is possible when the resources are sufficient and population have enough space to grow under no competition. Such curves are generally unrealistic in nature.

Growth B is possible when the population have enough resources to grow which gradually deplete with time. 

(b) Mention what does 'K' in the graph represent.

Answer: 'K' is the carrying capacity of a habitat for members of a given sort of organism.

20. Explain how are plants benefitted by their association with "Glomus species".

Answer: Glomus species benefits the plants and trees with their filaments. The Arbuscular mycorrhizal fungi help in increasing the surface area with their hyphae for absorption that supply proper nutrients to the plants. 

21. If the base adenine constitutes 31% of an isolated DNA fragment, then write what will be the expected percentage of the base cytosine in it. Explain how did you arrive at the answer given.

Answer: Cytosine= 19%

According to Chargaff’s rule in a DNA molecule A+T+G+C=100%

Percentage of A=Percentage of T

Percentage of G=Percentage of C

Therefore, If A=31% then, T=31%

G+C=38%

G=19% and C=19%