CBSE Class 12 Biology chapter-wise weightage
What the 2023–2026 board papers actually asked, chapter by chapter.
CBSE gives marks to units, not to chapters. Each unit below shows the marks CBSE’s 2025-26 syllabus gives it, and under it how the marks in the 2023–2026 papers actually split between its chapters.
| Chapter | 2023 | 2024 | 2025 | 2026 | Average |
|---|---|---|---|---|---|
| ReproductionCBSE: 16 of 70 marks (22.9%) · in the papers: 22.9% | |||||
| Sexual Reproduction in Flowering Plants | 8.6% | 8.1% | 10.1% | 9.9% | 9.2% |
| Human Reproduction | 7.7% | 10.1% | 8.6% | 10.4% | 9.2% |
| Reproductive Health | 4.8% | 6.4% | 3.6% | 3.4% | 4.5% |
| Genetics and EvolutionCBSE: 20 of 70 marks (28.6%) · in the papers: 32.1% | |||||
| Principles of Inheritance and Variation | 9.5% | 14.8% | 15.9% | 9.9% | 12.5% |
| Molecular Basis of Inheritance | 14.6% | 12.2% | 11.7% | 12.9% | 12.8% |
| Evolution | 9.2% | 4.9% | 5.5% | 7.2% | 6.7% |
| Biology and Human WelfareCBSE: 12 of 70 marks (17.1%) · in the papers: 15.9% | |||||
| Human Health and Disease | 9.5% | 10.2% | 9.3% | 10.9% | 10.0% |
| Microbes in Human Welfare | 6.3% | 5.7% | 5.0% | 6.8% | 5.9% |
| Biotechnology and its ApplicationsCBSE: 12 of 70 marks (17.1%) · in the papers: 16.4% | |||||
| Biotechnology : Principles and Processes | 7.7% | 8.1% | 8.2% | 10.2% | 8.6% |
| Biotechnology and its Applications | 8.0% | 7.8% | 9.9% | 5.6% | 7.8% |
| Ecology and EnvironmentCBSE: 10 of 70 marks (14.3%) · in the papers: 12.7% | |||||
| Organisms and Populations | 4.2% | 3.2% | 3.4% | 3.9% | 3.7% |
| Ecosystem | 2.7% | 4.2% | 3.1% | 4.3% | 3.6% |
| Biodiversity and Conservation | 7.1% | 4.2% | 5.8% | 4.7% | 5.5% |
How this is counted
From all 1,093 questions in the 2023–2026 CBSE Class 12 Biology papers we hold: every region and set, with a question printed in several sets counted once. A chapter’s share is its marks divided by all the marks of that year’s questions, and the average gives each year equal weight. These are observed shares, not an official CBSE weightage. 2022 is left out: it was the Term-II exam, which covered only part of the syllabus (see the 2022 paper).
Unit marks are CBSE’s own, from the 2025-26 syllabus. Where CBSE groups units under one figure, so does this table.