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CBSE Class 12th Biology Answer Key 2025, All SETs FREE PDF Download

CBSE Class 12th Biology Answer Key: This article will help students get the answer key for the CBSE Class 12th Biology exam. Students can check their answers here and calculate their total marks.

Mar 25, 2025, 14:32 IST

CBSE Class 12th Biology Answer Key 2025

CBSE Class 12th Biology Answer Key 2025: The CBSE Class 12 Biology Exam 2025 was held on March 19, 2025. As per the initial student reactions, the paper was moderately difficult. To help the students assess their performance, we provided the CBSE Class 12 Biology Answer Key 2025 in this article. The answer key has been prepared by subject experts and serves as an important resource for students to cross-check their answers and estimate their scores. Using the answer key allows students to learn from their mistakes and improve their preparation for future exams.

CBSE Class 12 Biology Exam Answer Key- Highlights

The CBSE Class 12 Biology question paper had 33 questions for 70 marks. The time allowed to write the paper was 3 hours. All questions were compulsory with some questions having internal choices.

Feature	Highlights
Board Name	Central Board Of Secondary Education (CBSE)
Exam Name	CBSE Class 12th Biology Exam
Exam Date	March 25, 2025
Duration	12:30 AM to 1:30 PM (3 hours)
Total Marks	70
Mode	Offline (Pen and Paper)
Time Duration	3 Hours
Question Paper Sets:	Multiple Sets (Set 1, Set 2, Set 3, Set 4)

Features Of CBSE Class 12th Biology Answer Key?

1. Self-Evaluation:

Students can compare their answers with the official solutions to understand their performance.

2. Score Estimation:

By checking the answer key, students can predict their approximate marks before the official results are announced.

3. Identify Mistakes:

Analysing incorrect answers helps students understand their weak areas for improvement in future exams.

Check:

CBSE Class 12 Biology Marking Scheme 2024-2025

Check the CBSE 12th Biology Marking Scheme 2025 in the table below.

Assessment Type	Marks
Theory Exam	70
Internal Assessment	30
Total	100

CBSE Class 12 Biology Answer Key 2025

Get here the complete answer key for CBSE Class 12th Biology Exam 2025 (SET-3)

1. Some flowers are unisexual, this property of unisexuality of flowers prevents which kind of pollination?
(A) Both Autogamy and Geitonogamy
(B) Both Geitonogamy and Xenogamy
(C) Geitonogamy but not Xenogamy
(D) Autogamy but not Geitonogamy

Correct Answer: (A) Both Autogamy and Geitonogamy

2. Given below is the schematic representation of spermatogenesis in human males:

Choose the option that shows the correct labelling of ‘I’, ‘II’, ‘III’ and ‘IV’ in the given diagram.

(A) I - Spermatogonia, II - Spermatid, III - Sec. Spermatocyte, IV - Spermatogonia
(B) I - Spermatid, II - Spermatogonia, III - Sec. Spermatocyte, IV - Spermatozoa
(C) I - Spermatogonia, II - Sec. Spermatocyte, III - Spermatozoa, IV - Spermatid
(D) I - Spermatogonia, II - Sec. Spermatocyte, III - Spermatid, IV - Spermatozoa

Correct Answer: (D) I - Spermatogonia, II - Sec. Spermatocyte, III - Spermatid, IV - Spermatozoa

3. Which one of the following options shows the correct evolutionary order of the plants mentioned below?

(i) Fern
(ii) Ginkgo
(iii) Zostrophyllum
(iv) Gnetales

(A) (iii), (i), (ii), (iv)
(B) (iii), (ii), (i), (iv)
(C) (ii), (i), (iii), (iv)
(D) (iv), (iii), (ii), (i)

Correct Answer: (A) (iii), (i), (ii), (iv)

4. In molecular biology, who proposed that genetic information flows in one direction?

(A) Har Gobind Khorana
(B) Francis Crick
(C) Watson and Crick
(D) Marshall Nirenberg

Correct Answer: (B) Francis Crick

5. Given below is a heterogeneous RNA formed during Eukaryotic transcription:

How many introns and exons respectively are present in the hnRNA?

(A) 7, 7
(B) 8, 7
(C) 8, 8
(D) 7, 8

Correct Answer: (D) 7, 8

6. Which of the following features correctly shows the mechanism of sex-determination in honey bees?

(i) A zygote formed from the union of a sperm and an egg develops into a male.
(ii) Males have half the number of chromosomes as that of females.
(iii) The females are diploid having 32 chromosomes.
(iv) Males have a father and can produce sons.

Choose the correct option:

(A) (i) and (ii)
(B) (ii) and (iii)
(C) (i) and (iv)
(D) (ii) and (iv)

Correct Answer: (B) (ii) and (iii)

7. Study the items of Column-I and those of Column-II:

Column-I	Column-II
(a) RNA polymerase I	(i) 18s rRNA
(b) RNA polymerase II	(ii) SnRNAs
(c) RNA polymerase III	(iii) hnRNA

Choose the option that correctly matches the items of Column-I with those of Column-II:

(A) (a) (ii), (b) (iii), (c) (i)
(B) (a) (i), (b) (iii), (c) (ii)
(C) (a) (iii), (b) (ii), (c) (i)
(D) (a) (ii), (b) (i), (c) (iii)

Correct Answer: (B) (a) (i), (b) (iii), (c) (ii)

8. A child with blood group A has a father with blood group B and the mother with blood group AB. Choose the option that gives the correct genotypes of father, mother, and the child:

Father	Mother	Child
(A) $I A i$	$I B i$	$I A i$
(B) $I A I B$	$I A i$	$I A I A$
(C) $I B i$	$I A I B$	$I A i$
(D) $I B I B$	$I A I B$	$I A I A$

Correct Answer: (C)

9. The decrease in the T-Lymphocytes count in human blood will finally result in

(A) decrease in antigens
(B) decrease in antibodies
(C) increase in antibodies
(D) increase in antigens

Correct Answer: (B) decrease in antibodies

10. If Meselson and Stahl’s experiment is continued for 80 minutes (till III generation), then what would be the ratio of DNA containing N¹⁵/N¹⁵ : N¹⁵/N¹⁴: N¹⁴/N¹⁴ in the medium?

(A) 1:1:0
(B) 0:1:3
(C) 1:2:0
(D) 1:4:0

Correct Answer: (B) 0:1:3

11. Select the correct statement from the following biotechnology procedures:

(A) The polymerase enzyme joins the gene of interest and the vector
(B) Gel electrophoresis is used for amplification of a DNA segment
(C) PCR is used for isolation and separation of the DNA segment
(D) Plasmid DNA acts as a vector to transfer the piece of DNA attached to it

Correct Answer: (D) Plasmid DNA acts as a vector to transfer the piece of DNA attached to it

12. For commercial and industrial production of citric acid, which one of the following microbes is used?

(A) Aspergillus niger
(B) Lactobacillus spp.
(C) Clostridium butylicum
(D) Saccharomyces cerevisiae

Correct Answer: (A) Aspergillus niger

13. Assertion (A): Corpus luteum secretes the hormone, progesterone.
Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.

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

14. Assertion (A): The number of white-winged moths decreased after industrialization in England.
Reason (R): Effects of industrialization were more marked in rural areas of England.

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

15. Assertion (A): Streptococcus pneumoniae and Haemophilus influenzae are responsible for causing infectious diseases in human beings.
Reason (R): A healthy person acquires the infection by inhaling the aerosols released by an infected person.

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

16. Assertion (A): Restriction endonuclease recognizes palindromic sequence in DNA and cuts them.

Reason (R): Palindromic sequence has two unique recognition sites PstI and PvuI recognized by restriction endonuclease.

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

SECTION – B

17. Student to attempt either option (A) or (B).

(A) Comment upon the mode of pollination in Vallisneria and Zostera.

(B) Mention any four strategies adopted by flowering plants to prevent self-pollination.

Correct Answer:

(A) Pollination in Vallisneria and Zostera:

Vallisneria follows hydrophily (water pollination) where the male flowers are released into the water and float to reach the female flowers.
Zostera also exhibits hydrophily, but its pollen grains are long, ribbon-like, and carried by water currents.

(B) Four strategies to prevent self-pollination:

Dichogamy: Stigma and anther mature at different times.
Herkogamy: Structural barriers prevent pollen from landing on the same flower’s stigma.
Self-incompatibility: Genetic mechanisms prevent self-pollen from fertilizing the ovule.
Unisexuality (Dioecy): Male and female flowers are on separate plants.

18. Study the given pedigree chart in which neither of the parents shows the trait, but the trait is present in both male and female children.

Answer the following questions:

(a) Write about the trait, also explain the inheritance of such trait in the progeny on the basis of the given pedigree chart.

(b) Give one example of such trait in human beings.

Correct Answer:

(a) Explanation of the Trait and Inheritance:

The given pedigree chart suggests an autosomal recessive inheritance, where both parents are carriers (heterozygous) but do not express the trait.
The affected children receive one recessive allele from each parent (homozygous recessive), leading to the expression of the trait.
This follows Mendel’s law of segregation, where 25% of offspring are affected when two carrier parents mate.

(b) Example of such trait in humans:

Sickle Cell Anemia
Cystic Fibrosis
Albinism

19. Student to attempt either option (A) or (B).

(A) Describe any two situations where a medical doctor would recommend injection of a pre-formed antibodies (antitoxins) into the body of a patient.

(B) The symptoms of malaria do not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles mosquito. Explain why it happens.

Correct Answer:

(A) Two situations where pre-formed antibodies (antitoxins) are recommended:

Tetanus Infection: If a person has a deep wound and is at risk of Clostridium tetani infection, tetanus antitoxin is administered to neutralize the toxins.
Snakebite: A person bitten by a venomous snake receives anti-venom, which consists of pre-formed antibodies against the snake's venom.

(B) Why malaria symptoms do not appear immediately after infection:

When a female Anopheles mosquito bites, it injects sporozoites into the bloodstream.
These sporozoites travel to the liver, where they undergo asexual multiplication (schizogony) inside liver cells.
After 5-7 days, merozoites are released into the bloodstream, invading red blood cells (RBCs).
The destruction of RBCs and release of toxins cause fever, chills, and sweating, which are the symptoms of malaria.