Biology Important Questions Class 12 CBSE 2026 — Chapter Wise
Class 12 Biology important questions 2026 — genetics crosses, ecological diagrams, reproduction flowcharts expected in CBSE boards.
CBSE Class 12 Biology board exam: 70 marks theory + 30 marks practical = 100 total. Genetics (18 marks) and Reproduction (14 marks) are the highest-weightage units. Below are the most expected questions from each chapter based on previous year paper analysis (2018–2025).
Chapter-Wise Marks Distribution
| Unit | Chapters | Marks |
|---|---|---|
| Reproduction | Reproduction in Organisms, Sexual Reproduction in Plants, Human Reproduction, Reproductive Health | 14 |
| Genetics & Evolution | Principles of Inheritance, Molecular Basis of Inheritance, Evolution | 18 |
| Biology & Human Welfare | Human Health & Disease, Microbes in Human Welfare, Biotechnology Principles, Biotechnology Applications | 14 |
| Biotechnology | Principles & Processes, Applications | 10 |
| Ecology | Organisms & Populations, Ecosystem, Biodiversity, Environmental Issues | 14 |
| Total (Theory) | 70 | |
Unit 1: Reproduction (14 marks)
Most Expected Questions
| Question Type | Topic | Marks |
|---|---|---|
| Diagram + explanation | Draw and describe the structure of a mature embryo sac (7-celled, 8-nucleate) | 3–5 |
| Diagram + explanation | Human male / female reproductive system with labelled diagram | 5 |
| Process description | Describe the process of fertilisation in humans | 3 |
| Differentiate | Spermatogenesis vs Oogenesis | 3 |
| Short answer | What is parthenocarpy? Give an example. | 2 |
| Short answer | Explain double fertilisation and triple fusion | 3 |
| Application | Methods of contraception — classify and explain | 5 |
| Short answer | What are STDs? Name 2 bacterial and 2 viral STDs. | 2 |
| Process | Explain the development of embryo from zygote to blastocyst | 3 |
| Application | Explain IVF and GIFT as assisted reproductive technologies | 3 |
Unit 2: Genetics & Evolution (18 marks)
Most Expected Questions
| Question Type | Topic | Marks |
|---|---|---|
| Numerical | Monohybrid / Dihybrid cross with Punnett square (phenotypic & genotypic ratios) | 5 |
| Explanation | Explain Mendel's Law of Segregation and Law of Independent Assortment | 3–5 |
| Diagram + process | Describe DNA replication with diagram (leading and lagging strand) | 5 |
| Diagram + process | Describe transcription in prokaryotes with diagram | 5 |
| Explanation | Explain the Central Dogma of molecular biology | 2–3 |
| Differentiate | Codominance vs Incomplete dominance with examples | 3 |
| Application | Explain sex-linked inheritance (colour blindness / haemophilia) with cross | 5 |
| Short answer | What is genetic code? List 4 properties of genetic code. | 2–3 |
| Explanation | Explain Hardy-Weinberg principle and factors affecting equilibrium | 3 |
| Short answer | What is operon concept? Explain lac operon with diagram. | 5 |
| Differentiate | Darwinism vs Neo-Darwinism | 3 |
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Start Biology Practice — FreeUnit 3: Biology & Human Welfare (14 marks)
| Question Type | Topic | Marks |
|---|---|---|
| Tabular | Differentiate between innate and acquired immunity | 3 |
| Explanation | Describe the life cycle of Plasmodium (malaria parasite) | 3–5 |
| Short answer | What is vaccination? How do vaccines work? | 2–3 |
| Application | Role of microbes in: biogas production, sewage treatment, antibiotics | 3–5 |
| Short answer | What are drugs and alcohol abuse? Discuss prevention and control. | 3 |
| Short answer | What is cancer? Differentiate between benign and malignant tumours. | 2–3 |
Unit 4: Biotechnology (10 marks)
| Question Type | Topic | Marks |
|---|---|---|
| Diagram + process | Describe the steps of recombinant DNA technology with diagram | 5 |
| Application | Applications of biotechnology in agriculture (Bt cotton, Golden Rice) | 3–5 |
| Short answer | What is PCR? Describe the 3 steps. | 3 |
| Explanation | What are restriction enzymes? How do they work? | 2–3 |
| Application | Gene therapy — explain with an example (ADA deficiency) | 3 |
| Short answer | What is gel electrophoresis? What is it used for? | 2 |
Unit 5: Ecology & Biodiversity (14 marks)
| Question Type | Topic | Marks |
|---|---|---|
| Diagram + explanation | Draw and explain ecological pyramids (number, biomass, energy) | 3–5 |
| Explanation | Describe the components and functions of an ecosystem | 5 |
| Process | Explain ecological succession — primary and secondary | 3 |
| Application | In-situ vs Ex-situ conservation strategies with examples | 3 |
| Short answer | What is biodiversity? Describe alpha, beta, and gamma diversity. | 3 |
| Application | Causes and effects of: deforestation, ozone depletion, greenhouse effect | 3–5 |
| Short answer | What are hotspots of biodiversity? Name 3 Indian hotspots. | 2 |
| Numerical | Energy flow — calculate energy at different trophic levels (10% rule) | 2–3 |
Must-Draw Diagrams
| Diagram | Chapter | Expected Marks |
|---|---|---|
| Mature embryo sac (7-celled, 8-nucleate) | Sexual Reproduction in Plants | 3 |
| Human male reproductive system | Human Reproduction | 3 |
| Human female reproductive system | Human Reproduction | 3 |
| DNA replication fork | Molecular Basis of Inheritance | 3 |
| Transcription process | Molecular Basis of Inheritance | 3 |
| Lac operon (on/off) | Molecular Basis of Inheritance | 3 |
| Ecological pyramids | Ecosystem | 3 |
| rDNA technology steps | Biotechnology Principles | 3 |
| Life cycle of Plasmodium | Human Health & Disease | 3 |
Diagram tip: Draw large (at least quarter-page size), use pencil for drawing, pen for labelling. Include title and at least 6 labels per diagram. A well-drawn diagram can rescue an otherwise weak answer.
Questions selected based on analysis of CBSE Class 12 Biology papers (2018–2025) and official 2026 sample paper. Marks distribution from CBSE 2025–2026 curriculum. Not all questions will appear — use this as a priority guide for revision. Last updated: February 2026.
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Start preparing — freeFrequently Asked Questions
Which chapters are most important for Class 12 Biology boards?
Top 5 by marks: Genetics & Evolution (18 marks), Reproduction (14 marks), Biology & Human Welfare (14 marks), Ecology & Biodiversity (14 marks), Biotechnology (10 marks). Genetics alone is 18/70 marks — master Mendelian genetics, molecular basis, and evolution thoroughly.
How many questions come from NCERT in Biology?
Almost all — 95%+ of board Biology questions are directly from NCERT textbooks. Many questions use exact NCERT phrases. Read every line, every diagram caption, and every in-text question. The back exercises are frequently tested. NCERT is both necessary and sufficient for Biology.
Are diagrams important in Biology board exam?
Extremely important. Well-labelled diagrams carry 2-3 marks each. Must-practise diagrams: DNA replication fork, transcription, human reproductive system (male & female), flower structure, ecological pyramids, biogas plant, PCR steps. Draw large, neat, and label clearly with a pen.
How to score full marks in Biology Class 12?
Strategy: (1) Read NCERT 3 times minimum, (2) Memorise all diagrams and flow charts, (3) Learn definitions word-for-word from NCERT, (4) Practise previous year questions (last 10 years), (5) Write answers in points with key terms underlined, (6) Include diagrams wherever possible — even if not asked, a relevant diagram adds marks.