CBSE 12 Biology Exam 2025-26: Most Important Assertion and Reason Questions with Answers for Last Minute Revision- Free PDF

The CBSE Class 12 Biology Board Exam is scheduled to be held on March 27, 2026. With very little time left for the exam, practicing the right questions is crucial for last-minute preparation.

This article is extremely important for students preparing for the CBSE Class 12 Biology examination in 2025-26. Assertion and Reason questions are crucial for scoring well in the board exams.

These questions test your conceptual understanding and strengthen your logical thinking. In this article, we have compiled important Assertion-Reason questions from all chapters.

You can download PDFs for free from the table below and further enhance your exam preparation.

CBSE Class 12 Biology Assertion Reason Questions 2025-26

Let’s look at an example to understand how these questions appear:

Two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Which of the following options is correct for the given statements?

Q. No.1: Assertion (A): Apomixis is an asexual mode of reproduction.

Reason (R): It involves the fusion of gametes.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q. No.2: Assertion(A): The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution.

Reason(R): Species diversity decreases as we move away from the equator towards the poles.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, but R is not the correct explanation of the assertion.

(c) A is true but R is false.

(d) R is true, but A is false.

Answer: (b) Both A and R are true, but R is not the correct explanation of the assertion.

Q. No.3: Assertion(A): Rivet popper hypothesis states that every species in an ecosystem is like a rivet and popper in an aeroplane.

Reason(R): Rivets present on the wings are more important than the rivets present on the seats.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, but R is not the correct explanation of the assertion.

(c) A is true but R is false.

(d) R is true, but A is false.

Answer: (b) Both A and R are true, but R is not the correct explanation of the assertion.

Q. No. 4: Assertion(A): Co-extinction is one reason for the loss of biodiversity.

Reason(R): When a host species becomes extinct, its unique assemblage of parasites also meets the same fate.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q. No. 5: Assertion(A): Ex-situ conservation refers to the on-site conservation of wildlife.

Reason(R): Zoological park is an example of ex-situ conservation.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q. No. 6: Assertion(A): Emigration results in a decrease in population density.

Reason(R): Emigration refers to the number of deaths in a population during a given time.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q .No. 7: Assertion(A): Cold-blooded animals do not have any fat layer.

Reason(R): They use their fat layer for the metabolic processes during hibernation.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q. No. 8: Assertion(A): Resources must be limited if the competition has to occur between species.

Reason(R): Totally unrelated species can compete for the same resource.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

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

Q. No. 9: Assertion(A): A majority of animals and nearly all plants cannot maintain a constant internal environment.

Reason(R): They are simply conformers.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (b) Both A and R are true, and R is not the correct explanation of the assertion.

Q. No. 10: Assertion(A): Recombinant DNA technology is used to produce a transgenic plant.

Reason(R): Transgenic organisms are the one that contains and express a transgene.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (b) Both A and R are true, and R is not the correct explanation of the assertion.

CBSE Class 12 Science Assertion and Reason Question PDF

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👉 CBSE Class 12 Study Materials

CBSE Class 12 study material includes latest syllabus, sample papers, NCERT books and solutions, previous year question papers, chapter-wise important questions, case study questions, assertion-reason questions, and competency-based questions — all updated as per the latest CBSE board exam pattern.