CBSE 12th Biology Assertion and Reason Questions: In recent years, CBSE has shifted its focus towards application-based and reasoning-oriented learning instead of rote memorisation and purely textbook theory. In order to implement this approach, Assertion & Reason (A&R) type questions have become an essential part of the question paper. These questions do not just test memory or definitions but check students’ conceptual clarity, logical reasoning, and ability to link two related statements. This type of assessment helps students think deeply, analyse information, and improve problem-solving skills. It also builds a stronger foundation for competitive exams and higher studies by focusing on understanding instead of rote learning. For the 2025-26 academic year, Assertion and Reason questions will remain an important part of the Class 12 Biology paper because they test analytical and reasoning skills. This article explains what Biology Assertion and Reason questions are, their format, examples, and preparation tips to help you study smartly and feel more confident in exams.
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What are CBSE Class 12 Biology Assertion and Reason Questions 2026?
CBSE Class 12 Biology Assertion and Reason questions go beyond textbook theory and memorised concepts. They are designed to test students’ understanding, critical thinking, and application skills. These types of questions have now become an important part of the exam pattern. They test not only students’ knowledge of facts but also their ability to understand relationships between concepts and apply logical reasoning.
Class 12 Biology Assertion and Reason questions are designed to test a student’s ability to:
- Apply biological concepts, processes, and principles to explain given statements.
- Evaluate whether the given Reason correctly explains the Assertion.
- Analyse relationships between concepts rather than simply recalling facts.
- Use critical thinking and logical reasoning to determine the truth or falsity of both statements.
CBSE Class 12 Biology Assertion and Reason Question Format
According to the CBSE Class 12 Biology Paper Pattern 2026, the paper includes:
- 4 Assertion and Reason-based questions, carrying 1 mark each.
- In Section A of the question paper
- In Assertion & Reason questions, there are two statements given:
Assertion (A): A statement presented as a fact. It may be true or false.
Reason (R): A supporting statement which may or may not correctly explain the Assertion. It can also be true or false.
Mainly, the students need to identify:
(a) Both assertion and reason are true, and the reason is the correct
explanation of the assertion.
(b) Both assertion and reason are true, but the reason is not the correct
explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Both assertion and reason are false.
These questions require students to understand the given case, extract relevant information, and solve accordingly.
Tips to Solve Biology Assertion and Reason Questions Effectively
To solve CBSE Class 12 Biology Assertion and Reason Questions effectively, first read the question carefully and understand both the statements given. Break the question into small parts and check the Assertion and Reason separately to see whether each is true or false, and whether the Reason statement explains the Assertion or not. Practise similar questions regularly to improve speed and accuracy. Here are some expert tips for solving Class 12 Biology Assertion and Reason questions effectively:
1. Read Both Statements Carefully: Understand the meaning of the Assertion and the Reason separately before comparing them.
2. Check the Truth of Each Statement: First decide if the Assertion is true or false, then check the Reason independently.
3. Find the Relationship: If both are true, see whether the Reason correctly explains the Assertion (cause-and-effect).
4. Eliminate Wrong Options: If confused, rule out obviously incorrect choices to narrow down the answer.
5. Practice from Sample Papers and Past Year Papers: Use the CBSE Sample Paper 2025 and previous years’ board papers to practice similar case-based questions.
CBSE Class 12 Biology Assertion and Reason Question
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 Biology Assertion and Reason Question PDF [Free]
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Common Mistakes to Avoid In Biology Assertion and Reason Questions
Many students lose marks in Biology Assertion and Reason questions because of small but avoidable mistakes. Knowing these mistakes in advance can help you approach such questions with more confidence and accuracy.
- Not reading both statements carefully: Skipping keywords like “always,” “never,” or “only” can change the meaning of the question.
- Assuming the Reason is correct without checking: Always verify both statements independently first.
- Confusing correlation with cause: Just because both statements are true doesn’t mean the Reason explains the Assertion.
- Relying on memorisation only: These questions test understanding; revise concepts and applications instead of rote learning.
- Not practising enough: Lack of practice with previous year and sample papers reduces speed and accuracy.
- Lack of practice: These questions are relatively new, and many students aren’t used to them yet.
CBSE Class 12 Biology Syllabus 2025-26
The Central Board of Secondary Education (CBSE) has released the Biology Syllabus for Class 12 Science streams for the 2025-26 academic year. This Biology Syllabus outlines the course structure, chapters, and topics that students will need to study in the subject. The CBSE Class 12 Biology syllabus covers a wide range of topics, including Reproduction, Genetics, Biology & Human Welfare, Biotechnology & its Applications and Ecology and Environment. It is divided into units with specific weightage, helping students plan their preparation effectively. The unit-wise chapters and weightage are provided below:
| Unit No. | Unit Name | Chapter Name | Marks |
| I | Reproduction | Sexual Reproduction in Flowering Plants Flower structure Human Reproduction Reproductive Health |
16 |
| II | Genetics and Evolution | Principles of Inheritance and Variation Heredity and variation Molecular Basis of Inheritance Evolution |
20 |
| III | Biology and Human Welfare | Human Health and Diseases Microbes in Human Welfare |
12 |
| IV | Biotechnology and its Applications | Biotechnology - Principles and Processes Biotechnology and its Applications |
12 |
| V | Ecology and Environment | Organisms and Populations Ecosystems Biodiversity and its Conservation |
10 |
| Total | 70 | ||
| Practical | 30 |
Check the latest and detailed CBSE Class 12 Biology Syllabus 2025-26; Check Latest Unit-wise Weightage, Download PDF.
CBSE Class 12 Biology Exam Pattern 2025
CBSE has released the exam pattern and marking scheme for the 2025-26 academic year. Based on the official question paper design shared the board has followed the same exam pattern and marking scheme as in 2024-25. The CBSE Class 12 Biology board exam for 2025-26 will also consists of a theory paper of 70 marks and a Practical of 30 marks. The question paper was divided into five different sections:
| Section | Question Type | Number of Questions | Marks |
| A | Multiple Choice Questions & Assertion and Reason Questions (1 mark) | 16 | 16 |
| B | Very Short Answer (2 mark) | 5 | 10 |
| C | Short Answer (3 marks) | 7 | 21 |
| D | Case Study-Based Questions (4 marks) | 2 | 8 |
| E | Long Answer (5 marks) | 3 | 15 |
| Total | 33 | 80 | |
Check the latest and detailed CBSE Class 12th Biology Exam Pattern 2025-26 with Marking Scheme.