In short: These 25 questions cover 70+ marks of the 70-mark CBSE Class 12 Biology theory paper. Each one comes from the official 2027 SQP pattern, previous year trends (2024-2026), and CBSE unit-wise marks allocation. Reproduction (14 marks), Genetics and Evolution (18 marks), Biology and Human Welfare (14 marks), Biotechnology (11 marks), and Ecology (13 marks) — every high-probability question type is here. Practice each one. Know the diagrams. Score the marks that are waiting. Also see our Chemistry expected questions for Class 12.
How This List Was Built
| Source | What We Analysed |
|---|---|
| CBSE Official SQP 2027 | Released Sep 21, 2026. 33 questions across 5 sections (16 MCQs, 5 two-mark, 7 three-mark, 2 case-based, 3 five-mark). |
| Previous Year Papers (2024-2026) | 3 years of board papers. Repeated question types and diagrams identified. |
| CBSE Unit-Wise Weightage | Reproduction = 14 marks. Genetics + Evolution = 18 marks. Biology in Human Welfare = 14 marks. Biotechnology = 11 marks. Ecology = 13 marks. See the full chapter-wise weightage breakdown. |
| SQP Marking Scheme | Step-wise marks for diagrams, processes, and explanations. |
Unit-Wise Expected Marks Distribution
| Unit | Chapters | Expected Marks | Questions in This List |
|---|---|---|---|
| Reproduction | Sexual Reproduction in Flowering Plants, Human Reproduction, Reproductive Health | 14 | #1-5 |
| Genetics and Evolution | Inheritance, Molecular Basis of Inheritance, Evolution | 18 | #6-12 |
| Biology and Human Welfare | Health and Disease, Microbes in Human Welfare, Strategies for Food Enhancement | 14 | #13-16 |
| Biotechnology | Principles and Processes, Applications | 11 | #17-20 |
| Ecology | Organisms and Populations, Ecosystem, Biodiversity, Environmental Issues | 13 | #21-25 |
| Total | 70 | 25 questions |
Reproduction — Sexual Reproduction in Flowering Plants (5 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 1 | Draw a labelled diagram of a mature embryo sac (7-celled, 8-nucleate). Explain the role of each cell type in fertilization. | LA | 5 | D |
| 2 | Describe the process of double fertilization in angiosperms. What is triple fusion? What is the significance of double fertilization? | SA | 3 | C |
| 3 | Draw a labelled diagram of the L.S. of an anatropous ovule. Label: integuments, micropyle, chalaza, nucellus, embryo sac, funicle. | SA | 3 | C |
What the examiner wants
- Q1: The diagram MUST show all 7 cells: egg cell, 2 synergids (with filiform apparatus), 3 antipodal cells, central cell with 2 polar nuclei. This diagram appeared in board papers in 2024, 2025, AND 2026. It is the #1 most repeated Biology diagram.
- Q2: Double fertilization = one male gamete fuses with egg (forms zygote → embryo), other fuses with polar nuclei (forms PEN → endosperm). Significance: endosperm provides nutrition. Write exactly 3-4 steps.
PYQ pattern
Embryo sac diagram OR double fertilization explanation appeared in every board paper from 2022 to 2026. This is the single most guaranteed question in the entire Biology paper.
Reproduction — Human Reproduction (5 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 4 | Draw a labelled diagram of the human male reproductive system OR human female reproductive system. Describe the role of any 3 labelled parts. | LA / SA | 3-5 | C / D |
| 5 | Describe the events of the menstrual cycle: menstrual phase, follicular phase, ovulatory phase, luteal phase. Include the role of hormones (FSH, LH, estrogen, progesterone). | LA | 5 | D |
What the examiner wants
- Q4: Diagram must be clean and large with at least 8 labels. For male: testis, epididymis, vas deferens, seminal vesicle, prostate, urethra, penis. For female: ovary, fallopian tube (fimbriae, ampulla, isthmus), uterus, cervix, vagina. Role description = 1 mark per part.
- Q5: 4 phases of menstrual cycle with days: menstrual (1-5), follicular (6-13), ovulatory (14), luteal (15-28). Hormone graph if asked: FSH/LH spike at ovulation, estrogen peaks before ovulation, progesterone peaks during luteal phase.
PYQ pattern
Menstrual cycle with hormone roles appeared in 2024 and 2026. Male/female reproductive system diagram appeared in 2025.
Reproduction — Reproductive Health (4 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 6 | Explain any 4 methods of contraception with one example each (barrier, hormonal, IUD, surgical). | SA | 3 | C |
What the examiner wants
- Barrier: condoms, diaphragm. Hormonal: oral pills (estrogen + progesterone). IUD: Copper-T. Surgical: vasectomy (male), tubectomy (female). 4 methods × 1 mark each. Use table format for clarity.
Genetics — Principles of Inheritance and Variation (8 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 7 | A cross between two organisms produces the following phenotypic ratio. Identify the type of inheritance and give the genotypes. (Typically: incomplete dominance 1:2:1, codominance, complementary genes) | SA / LA | 3-5 | C / D |
| 8 | Explain sex determination in humans with a diagram (XX-XY mechanism). Why is the father responsible for the sex of the child? | SA | 3 | C |
| 9 | Explain the chromosomal basis of any two genetic disorders: Down syndrome (trisomy 21), Turner syndrome (45,X), Klinefelter syndrome (47,XXY). | VSA / SA | 2-3 | B / C |
What the examiner wants
- Q7: Draw the Punnett square. Show P generation, F1, F2. Write genotypic AND phenotypic ratios. Identify the specific type (incomplete dominance = both alleles express partially; codominance = both express fully).
- Q8: Diagram showing father (XY) × mother (XX). Show 4 possible offspring: XX, XX, XY, XY. 50% chance of boy or girl. Father contributes X or Y — hence determines sex.
PYQ pattern
Punnett square problems appeared in 3/3 years. Sex determination diagram appeared in 2/3 years. These are near-certain questions.
Genetics — Molecular Basis of Inheritance (10 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 10 | Draw a labelled diagram of the DNA double helix. Explain the base pairing rules and the semi-conservative nature of DNA replication. | LA | 5 | D |
| 11 | Describe the process of transcription in eukaryotes. Include: template strand, RNA polymerase, promoter, terminator, post-transcriptional processing (capping, tailing, splicing). | SA / LA | 3-5 | C / D |
| 12 | Explain the Lac Operon model with a labelled diagram. Describe its regulation in the presence and absence of lactose (inducer). | LA | 5 | D |
What the examiner wants
- Q10: DNA diagram: sugar-phosphate backbone, complementary base pairs (A-T with 2 H-bonds, G-C with 3 H-bonds), antiparallel strands (5'→3' and 3'→5'), major and minor grooves. Semi-conservative = each daughter molecule has one old strand and one new strand (Meselson-Stahl experiment reference).
- Q12: Lac Operon = THE most asked molecular biology question. Label: structural genes (z, y, a), operator, promoter, regulator gene (i gene). Without inducer: repressor binds operator, blocks transcription. With lactose: lactose (allolactose) binds repressor, changes shape, cannot bind operator, RNA polymerase transcribes genes.
PYQ pattern
Lac Operon appeared in 2024 AND 2026 (every alternate year). DNA replication or transcription appeared every year. Combined, molecular biology contributes 8-10 marks.
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Biology in Human Welfare — Human Health and Disease (8 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 13 | Differentiate between innate and acquired immunity. Describe the types of acquired immunity (active vs passive, natural vs artificial). | SA | 3 | C |
| 14 | Name the causative organism, mode of transmission, symptoms, and prevention for any 2 diseases: malaria, typhoid, pneumonia, amoebiasis, filariasis. | Case-based / MCQ | 1-4 | A / E |
| 15 | What are the harmful effects of drug and alcohol abuse? Explain prevention and control measures. | SA | 2-3 | B / C |
What the examiner wants
- Q13: Innate = born with it (skin, mucus, HCl in stomach, WBCs). Acquired = develops after exposure (B-cells → antibodies, T-cells → cell-mediated). Active = body makes antibodies (vaccination, infection). Passive = antibodies given directly (mother's milk, antivenom).
- Q14: Use table format: Disease | Pathogen | Vector/Transmission | Symptoms | Prevention. One row per disease = full marks.
Biology in Human Welfare — Microbes in Human Welfare (6 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 16 | Name the microorganism and the product it produces in: (a) cheese ripening, (b) ethanol production, (c) antibiotic production, (d) biogas generation, (e) sewage treatment. | MCQ / VSA / SA | 1-3 | A / B / C |
What the examiner wants
- Table format: (a) Propionibacterium shermanii → Swiss cheese. (b) Saccharomyces cerevisiae → ethanol. (c) Penicillium notatum → penicillin. (d) Methanobacterium → biogas (methane). (e) Heterotrophic microbes → activated sludge process → BOD reduction.
Biotechnology — Principles and Processes (6 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 17 | Describe the steps of Recombinant DNA Technology: isolation of DNA, cutting with restriction enzymes, ligation, transformation, selection, cloning. | LA | 5 | D |
| 18 | Explain PCR (Polymerase Chain Reaction) with a diagram. Name the 3 steps of each cycle (denaturation, annealing, extension) and the enzyme used (Taq polymerase). | SA | 3 | C |
What the examiner wants
- Q17: 6 steps in sequence. Each step = ~1 mark. Mention specific tools: restriction endonuclease (EcoRI), ligase, plasmid vector (pBR322), selectable markers (antibiotic resistance), host organism (E. coli). Diagram of the process earns extra marks.
- Q18: PCR diagram showing 3 steps with temperatures: denaturation (94°C), annealing (55-65°C), extension (72°C). Taq polymerase = thermostable. Each cycle doubles the DNA.
PYQ pattern
rDNA technology steps OR PCR appeared every year. Combined = 5-8 marks guaranteed.
Biotechnology — Applications (5 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 19 | What is Bt cotton? Explain how Bt toxin gene was introduced into cotton plants and how it protects against bollworm. | SA | 3 | C |
| 20 | What is gene therapy? Describe the treatment of ADA deficiency using gene therapy. OR explain the process of producing human insulin through rDNA technology. | SA / Case-based | 2-3 | B / C / E |
What the examiner wants
- Q19: Bt = Bacillus thuringiensis. cry gene (cry1Ac for bollworm). Gene inserted into cotton plant using Agrobacterium-mediated transformation. Bt protein is inactive in plant but becomes active in insect gut (alkaline pH) → binds to midgut epithelium → creates pores → insect dies.
- Q20: ADA deficiency: Adenosine Deaminase enzyme missing → SCID (Severe Combined Immunodeficiency). Gene therapy: functional ADA gene inserted into patient's lymphocytes using retroviral vector → lymphocytes reintroduced → produce ADA enzyme.
Ecology — Organisms and Populations (4 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 21 | Draw and explain the logistic growth curve (S-curve). Write the equation: dN/dt = rN(K-N)/K. Define r, N, K. How does it differ from exponential growth (J-curve)? | SA | 3 | C |
What the examiner wants
- J-curve: unlimited resources, dN/dt = rN. S-curve: limited resources, carrying capacity K. Draw both curves on the same graph. Label asymptote at K. The equation and graph together = 3 marks.
Ecology — Ecosystem (5 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 22 | Describe the energy flow through an ecosystem. Explain the 10% law (Lindeman's rule). Draw an ecological pyramid of energy. Why is it always upright? | SA / LA | 3-5 | C / D |
| 23 | Describe the process of decomposition in an ecosystem: fragmentation, leaching, catabolism, humification, mineralization. | SA | 2-3 | B / C |
What the examiner wants
- Q22: Energy flow is unidirectional. Only 10% passes to next trophic level. Pyramid of energy is ALWAYS upright (unlike biomass or numbers which can be inverted). Draw: Producers (1000 kcal) → Primary consumers (100 kcal) → Secondary (10 kcal) → Tertiary (1 kcal).
- Q23: 5 steps in sequence: Fragmentation (detritivores break down) → Leaching (water-soluble nutrients seep) → Catabolism (enzymes degrade) → Humification (dark huite-resistant humus) → Mineralization (humus → inorganic nutrients).
Ecology — Biodiversity and Environmental Issues (4 Marks)
| # | Expected Question | Type | Marks | Section |
|---|---|---|---|---|
| 24 | What are the major causes of biodiversity loss? Explain any 3: habitat loss, overexploitation, alien species invasion, co-extinctions. | SA | 3 | C |
| 25 | What is the greenhouse effect? Name 3 greenhouse gases. Explain how enhanced greenhouse effect leads to global warming. OR describe ozone depletion and its effects. | MCQ / SA / Case-based | 1-4 | A / C / E |
What the examiner wants
- Q24: Habitat loss = #1 cause (deforestation, urbanization). Overexploitation = hunting, overfishing. Alien species = water hyacinth in India, Nile perch in Lake Victoria. Co-extinctions = when one species goes extinct, dependent species follow.
- Q25: Greenhouse gases: CO₂, CH₄, N₂O, CFCs. Enhanced greenhouse effect = increased concentration of these gases → traps more infrared radiation → global temperature rise. Ozone depletion = CFCs release Cl atoms → Cl destroys O₃ → UV radiation reaches Earth → skin cancer, cataracts.
30-Day Practice Plan
| Week | Focus | Questions from This List | Practice Papers |
|---|---|---|---|
| Week 1 | Reproduction (Chapters 1-4) + Diagrams | #1-6 (embryo sac, menstrual cycle, reproductive systems) | 0 — focus on concept + diagram mastery |
| Week 2 | Genetics + Molecular Biology (Chapters 5-7) | #7-12 (Punnett squares, DNA, Lac Operon) | 1 full paper |
| Week 3 | Human Welfare + Biotechnology (Chapters 8-12) | #13-20 (immunity, microbes, rDNA, PCR, Bt cotton) | 1 full paper |
| Week 4 | Ecology (Chapters 13-16) + Full Revision | #21-25 (energy flow, decomposition, biodiversity) | 2-3 full papers |
Section-Wise Time Strategy on Exam Day
| Section | Questions | Marks | Time | Strategy |
|---|---|---|---|---|
| A (MCQ + A-R) | 16 | 16 | 18 min | Quick recall. Diagrams in mind help. |
| B (VSA - 2 marks) | 5 | 10 | 12 min | One-two lines. Direct definitions. |
| E (Case-Based) | 2 | 8 | 15 min | Do BEFORE Section D. Read case carefully. |
| C (SA - 3 marks) | 7 | 21 | 30 min | Diagram-based answers get full marks faster. |
| D (LA - 5 marks) | 3 | 15 | 30 min | Embryo sac, Lac Operon, rDNA technology, energy flow. |
| Review | — | — | 15 min | Check diagram labels, verify scientific names. |
The 10 Diagrams You MUST Know
| # | Diagram | Chapter | Marks | Frequency (2024-2026) |
|---|---|---|---|---|
| 1 | Mature embryo sac (7-celled, 8-nucleate) | Ch 2 | 3-5 | 3/3 years |
| 2 | L.S. of anatropous ovule | Ch 2 | 3 | 2/3 years |
| 3 | Human male or female reproductive system | Ch 3 | 3-5 | 3/3 years |
| 4 | DNA double helix structure | Ch 6 | 3-5 | 2/3 years |
| 5 | Lac Operon (with and without inducer) | Ch 6 | 5 | 2/3 years |
| 6 | DNA replication fork | Ch 6 | 3 | 2/3 years |
| 7 | Transcription process | Ch 6 | 3 | 2/3 years |
| 8 | Steps of rDNA technology (flowchart) | Ch 11 | 5 | 3/3 years |
| 9 | PCR cycle diagram | Ch 11 | 3 | 2/3 years |
| 10 | Ecological pyramid of energy | Ch 14 | 2-3 | 2/3 years |
If you can draw and label all 10 diagrams from memory, you can score 25-30 marks from diagrams alone. For NEET aspirants, also check our 50 important Biology diagrams you must know for NEET.
Frequently Asked Questions
Q1. Which unit has the highest marks in Biology? Genetics and Evolution carries 18 marks — the highest. Molecular Basis of Inheritance (Chapter 6) alone can contribute 8-10 marks through DNA structure, replication, transcription, translation, and Lac Operon. Master this chapter first.
Q2. Are diagrams really that important in Biology? Yes. Diagrams carry 20-30 marks directly (labelled diagram questions) and contribute to another 10-15 marks indirectly (supporting diagrams in answers). A Biology answer without a diagram when one is relevant = lost marks.
Q3. How should I study the Human Health and Disease chapter? Use tables: Disease | Pathogen | Transmission | Symptoms | Prevention. Learn the table format and you can answer any question from this chapter in 2 minutes. Do not memorize paragraphs.
Q4. Is the SQP pattern the same as the actual board paper? CBSE confirmed the same assessment pattern for 2027. The question types, marks distribution, and section structure will match the SQP. Specific questions will differ but the format is identical. For a detailed comparison of how closely the SQP matches the actual paper, see our SQP vs actual paper analysis.
Q5. What is the best way to revise Biology in the last week? Diagram dump: draw all 10 must-know diagrams from memory once a day. Flowchart revision: rDNA technology steps, PCR steps, menstrual cycle, Lac Operon regulation. Table revision: diseases, microbes and their products, contraception methods. Skip re-reading chapters — active recall beats passive reading.
Q6. Should I attempt all questions even if I am not sure? Yes. No negative marking. Write the diagram, write the key terms, write the first step. Partial marks are given for correct terminology, relevant diagrams, and logical flow — even if the complete answer is not there. For tips on how to present answers for maximum marks, read our answer sheet guide.
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