For students preparing for the CBSE Class 12 Biology board examination, understanding the marks distribution is an important part of planning revision. The Biology syllabus for the 2026-27 academic session carries 100 marks in total, with 70 marks allotted to theory and 30 marks to the practical examination. The theory paper is of three hours' duration.
The unit-wise distribution gives students a clear idea of how the 70 theory marks are spread across the syllabus.
| Unit | Chapter/Area | Marks |
|---|---|---|
| VI | Reproduction | 16 |
| VII | Genetics and Evolution | 20 |
| VIII | Biology and Human Welfare | 12 |
| IX | Biotechnology and its Applications | 12 |
| X | Ecology and Environment | 10 |
| Total | 70 |
As per the CBSE course structure, Genetics and Evolution carries the highest weightage at 20 marks, followed by Reproduction with 16 marks. Biology and Human Welfare and Biotechnology and its Applications carry 12 marks each, while Ecology and Environment carries 10 marks.
Which Biology Units Need More Attention?
The marks distribution can help students organise their preparation time. Genetics and Evolution includes Principles of Inheritance and Variation, Molecular Basis of Inheritance and Evolution. These topics cover areas such as Mendelian inheritance, DNA and RNA, replication, transcription, translation, gene expression and mechanisms of evolution.
Reproduction, carrying 16 marks, covers Sexual Reproduction in Flowering Plants, Human Reproduction and Reproductive Health.
The remaining units cover human health and diseases, microbes, biotechnology, organisms and populations, ecosystems and biodiversity.
Students should remember that unit-wise weightage does not mean that questions can be predicted chapter by chapter. The complete prescribed syllabus should be prepared.
CBSE Class 12 Biology Question Paper Pattern 2026-27
The 2026-27 question paper design divides the theory assessment according to three broad competencies:
Demonstrate Knowledge and Understanding – 50%
Application of Knowledge/Concepts – 30%
Analyse, Evaluate and Create – 20%
The paper may include very short-answer questions, MCQs, assertion-reasoning questions, short-answer questions, long-answer questions and source-, case-, passage- or integrated-assessment questions. CBSE has also specified approximately 33% internal choice.
| Practical Component | Marks |
|---|---|
| One Major Experiment | 5 |
| One Minor Experiment | 4 |
| Slide Preparation | 5 |
| Spotting | 7 |
| Practical Record + Viva Voce | 4 |
| Investigatory Project, Project Record + Viva Voce | 5 |
| Total | 30 |
A simple preparation strategy is to:
Complete Genetics and Evolution and Reproduction carefully.
Make short revision notes for important definitions, processes and diagrams.
Practise application and case-based questions rather than relying only on direct questions.
Revise the remaining three units systematically.
Give adequate attention to practical experiments, spotting, viva and the investigatory project.
Use CBSE sample papers and marking schemes to become familiar with the expected question style. CBSE has published the 2026-27 Class XII Sample Question Papers and Marking Schemes, including Biology.