Biology Important Questions Class 12 CBSE — Chapter Wise
CBSE Class 12 Biology important questions, unit by unit: genetics crosses, key diagrams, reproduction, biotechnology and ecology, with 2026-27 unit marks.
CBSE Class 12 Biology is 70 marks theory + 30 marks practical. Genetics and Evolution (20 marks) and Reproduction (16) are the biggest units. Below are the question types that come up often in each unit, to guide your revision for the Board exams 2027.
Unit-Wise Marks (2026-27)
| Unit | Chapters | Marks |
|---|---|---|
| Reproduction | Sexual Reproduction in Flowering Plants, Human Reproduction, Reproductive Health | 16 |
| Genetics & Evolution | Principles of Inheritance and Variation, Molecular Basis of Inheritance, Evolution | 20 |
| Biology & Human Welfare | Human Health and Disease, Microbes in Human Welfare | 12 |
| Biotechnology | Biotechnology: Principles and Processes, Biotechnology and its Applications | 12 |
| Ecology & Environment | Organisms and Populations, Ecosystem, Biodiversity and its Conservation | 10 |
| Total (Theory) | 70 | |
Environmental Issues is assessed only by your school, and Reproduction in Organisms is not in the syllabus.
Reproduction (16 marks)
| Question type | Topic |
|---|---|
| Diagram + explanation | Structure of a mature embryo sac (7-celled, 8-nucleate) |
| Diagram + explanation | Human male or female reproductive system, labelled |
| Differentiate | Spermatogenesis vs oogenesis |
| Short answer | Double fertilisation and triple fusion |
| Short answer | Parthenocarpy, apomixis and polyembryony, with examples |
| Process | Fertilisation and development of the embryo up to the blastocyst and implantation |
| Application | Methods of contraception — classify and explain |
| Application | Assisted reproductive technologies — IVF, ZIFT, GIFT |
Genetics & Evolution (20 marks)
| Question type | Topic |
|---|---|
| Cross | Monohybrid or dihybrid cross with Punnett square — phenotypic and genotypic ratios |
| Explanation | Mendel's laws of segregation and independent assortment |
| Differentiate | Incomplete dominance vs co-dominance, with examples; multiple alleles and blood groups |
| Application | Sex-linked inheritance (haemophilia, colour blindness) with a cross |
| Diagram + process | DNA replication, with the replication fork |
| Diagram + process | Transcription and the lac operon |
| Short answer | Features of the genetic code; the central dogma |
| Explanation | Hardy–Weinberg principle and the factors that disturb equilibrium |
| Explanation | Darwin's contribution, natural selection and the modern synthetic theory |
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Start freeBiology & Human Welfare (12 marks)
| Question type | Topic |
|---|---|
| Tabular | Innate vs acquired immunity; active vs passive immunity |
| Explanation | Life cycle of Plasmodium (malaria) |
| Short answer | How vaccines work |
| Short answer | Cancer — benign vs malignant tumours; HIV and AIDS |
| Short answer | Drug and alcohol abuse in adolescence — effects and prevention |
| Application | Microbes in sewage treatment, biogas production and antibiotics |
Biotechnology (12 marks)
| Question type | Topic |
|---|---|
| Diagram + process | Steps of recombinant DNA technology |
| Short answer | PCR — the three steps |
| Explanation | Restriction enzymes and how they work |
| Short answer | Gel electrophoresis and what it is used for |
| Application | Bt crops, human insulin production and gene therapy (ADA deficiency) |
| Short answer | Biosafety issues, biopiracy and patents |
Ecology & Environment (10 marks)
| Question type | Topic |
|---|---|
| Diagram + explanation | Ecological pyramids — number, biomass and energy |
| Numerical | Energy flow between trophic levels (10% law) |
| Explanation | Productivity and decomposition |
| Short answer | Population interactions — mutualism, competition, predation, parasitism |
| Application | In-situ vs ex-situ conservation, with examples |
| Short answer | Biodiversity hotspots, sacred groves and causes of biodiversity loss |
Must-Practise Diagrams
- Mature embryo sac — Sexual Reproduction in Flowering Plants
- Human male and female reproductive systems — Human Reproduction
- DNA replication fork and the lac operon — Molecular Basis of Inheritance
- Ecological pyramids — Ecosystem
- Steps of recombinant DNA technology — Biotechnology: Principles and Processes
- Life cycle of Plasmodium — Human Health and Disease
Diagram tip: draw large, use pencil for the drawing and pen for labels, and add a title. Clear labels matter as much as the drawing.
For chapter-wise practice, see our CBSE Class 12 Biology important questions pages.
Unit marks and topics from the CBSE Class XII Biology syllabus 2026-27 (cbseacademic.nic.in). These are common question types, not predictions — questions can come from any part of the syllabus.
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Start freeFrequently Asked Questions
Which units carry the most marks in Class 12 Biology?
In the 2026-27 syllabus: Genetics and Evolution 20, Reproduction 16, Biology and Human Welfare 12, Biotechnology 12, and Ecology and Environment 10 — 70 marks in all. Genetics alone is over a quarter of the paper, so master Mendelian crosses, the molecular basis of inheritance and evolution.
How important is NCERT for Class 12 Biology?
Very. Most board Biology questions are built closely on the NCERT textbook, often using its terms and examples. Read every line, diagram and in-text question, and do the end-of-chapter exercises. The competency-based questions then test whether you can apply that content.
Are diagrams important in the Biology board exam?
Yes. Labelled diagrams earn marks where a question asks for them and make descriptive answers clearer. Practise the DNA replication fork, the human reproductive systems, the embryo sac, ecological pyramids and the steps of recombinant DNA technology. Draw large, neat and clearly labelled.
How do I score full marks in Class 12 Biology?
Read NCERT several times, practise the key diagrams and flow charts, learn definitions precisely, solve the 2026-27 CBSE sample paper and recent board papers, and write answers in points with key terms underlined. Prepare well for the 30-mark practical too.