CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 1
CLASS 12 CBSE BIOLOGY
MOST IMPORTANT QUESTIONS
Board Exam Preparation 2025-26
10 Chapters | 100 Questions | Rapid Fire Top 50 | Last-Minute Notes
NCERT-Based | Previous Year Questions | Score 90%+
CBSE Board Exam Preparation 2025-26 | Score 90%+
,CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 2
TABLE OF CONTENTS
■ Chapter 1: Sexual Reproduction in Flowering Plants
■ Chapter 2: Human Reproduction
■ Chapter 3: Reproductive Health
■ Chapter 4: Principles of Inheritance and Variation
■ Chapter 5: Molecular Basis of Inheritance
■ Chapter 6: Evolution
■ Chapter 7: Human Health and Disease
■ Chapter 8: Microbes in Human Welfare
■ Chapter 9: Biotechnology: Principles and Applications
■ Chapter 10: Ecology: Organisms and Ecosystems
Rapid Fire — Top 50 Most Expected Questions
Last-Minute Revision Notes
Board Exam Tips
CBSE Board Exam Preparation 2025-26 | Score 90%+
,CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 3
■ CHAPTER 1: SEXUAL REPRODUCTION IN FLOWERING
PLANTS
Q1 [MCQ]
Which part of the flower develops into the fruit after fertilisation?
Answer: Ovary
Explanation: After double fertilisation, the ovary wall (pericarp) develops into the fruit. The ovule
develops into the seed.
Board Tip: Ovary to Fruit | Ovule to Seed — 1-mark question every year
Q2 [Short Answer]
What is double fertilisation? Write the chromosome numbers of the products. (2 marks)
Answer: Two fusions: (1) Syngamy — male gamete + egg = Zygote (2n). (2) Triple fusion —
2nd male gamete + 2 polar nuclei = Primary Endosperm Nucleus PEN (3n).
Explanation: Discovered by Nawaschin (1898). Unique to angiosperms. Zygote forms embryo; PEN
forms endosperm.
Board Tip: Always write 2n for zygote and 3n for PEN — examiner checks chromosome numbers
Q3 [Assertion-Reason]
A: Pollination and fertilisation are different events.
R: Pollination is transfer of pollen to stigma; fertilisation is fusion of gametes inside the ovule.
Options: (a) Both true, R explains A (b) Both true, R doesn't explain (c) A true R false (d) A false R
true
Answer: (a) Both A and R are true and R is the correct explanation.
Explanation: Pollination = pre-fertilisation event on stigma. Fertilisation = inside embryo sac. R correctly
explains A.
Q4 [MCQ]
The nutritive tissue formed after triple fusion in angiosperms is called:
Answer: Endosperm (3n — triploid)
Explanation: Endosperm is 3n, formed from PEN. In coconut, liquid endosperm = coconut water; solid =
copra.
CBSE Board Exam Preparation 2025-26 | Score 90%+
, CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 4
Q5 [Short Answer]
What is apomixis? Give one agricultural application. (2 marks)
Answer: Apomixis = production of seeds without fertilisation (asexual seed formation).
Application: Preserves superior hybrid traits — no need to buy hybrid seeds every year.
Seeds breed true.
Explanation: Found in Asteraceae and Gramineae. Apomixis + hybrid vigour = major advantage in crop
production.
Q6 [Short Answer]
Distinguish between self-pollination and cross-pollination. Give one example each. (3 marks)
Answer: Self-pollination: pollen from same flower/plant to its stigma. E.g., Wheat, Pea.
Cross-pollination: pollen from different plant of same species. E.g., Maize. Cross-pollination
promotes genetic variation and hybrid vigour.
Explanation: Adaptations for cross-pollination: Dichogamy, Herkogamy, Self-incompatibility, Dioecy.
Q7 [Case-Based]
Priya noticed some orchids mimic female insects — no nectar reward, yet get pollinated by male
bees.
(i) Name this pollination strategy.
(ii) Is this mutualism? Justify.
(iii) Name the pollinating agent.
Answer: (i) Deceptive/Floral mimicry pollination. (ii) No — only plant benefits, bee gets no
reward — one-sided. (iii) Insects (entomophily — bees).
Explanation: Reward-less flowers use deception. These test HOTS in case-based questions.
Q8 [Long Answer]
Describe the structure of a mature angiosperm embryo sac with a labelled diagram. (5 marks)
Answer: 7-celled, 8-nucleate: (1) Egg apparatus — 1 egg cell + 2 synergids (micropylar end).
(2) Central cell — 2 polar nuclei. (3) 3 antipodal cells (chalazal end). Synergids have filiform
apparatus. Polar nuclei fuse to form secondary nucleus.
Explanation: Diagram must label: egg cell, synergids, antipodals, central cell, polar nuclei, micropylar
end, chalazal end.
Board Tip: 7 cells, 8 nuclei — memorise this fact
Q9 [MCQ]
CBSE Board Exam Preparation 2025-26 | Score 90%+
CLASS 12 CBSE BIOLOGY
MOST IMPORTANT QUESTIONS
Board Exam Preparation 2025-26
10 Chapters | 100 Questions | Rapid Fire Top 50 | Last-Minute Notes
NCERT-Based | Previous Year Questions | Score 90%+
CBSE Board Exam Preparation 2025-26 | Score 90%+
,CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 2
TABLE OF CONTENTS
■ Chapter 1: Sexual Reproduction in Flowering Plants
■ Chapter 2: Human Reproduction
■ Chapter 3: Reproductive Health
■ Chapter 4: Principles of Inheritance and Variation
■ Chapter 5: Molecular Basis of Inheritance
■ Chapter 6: Evolution
■ Chapter 7: Human Health and Disease
■ Chapter 8: Microbes in Human Welfare
■ Chapter 9: Biotechnology: Principles and Applications
■ Chapter 10: Ecology: Organisms and Ecosystems
Rapid Fire — Top 50 Most Expected Questions
Last-Minute Revision Notes
Board Exam Tips
CBSE Board Exam Preparation 2025-26 | Score 90%+
,CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 3
■ CHAPTER 1: SEXUAL REPRODUCTION IN FLOWERING
PLANTS
Q1 [MCQ]
Which part of the flower develops into the fruit after fertilisation?
Answer: Ovary
Explanation: After double fertilisation, the ovary wall (pericarp) develops into the fruit. The ovule
develops into the seed.
Board Tip: Ovary to Fruit | Ovule to Seed — 1-mark question every year
Q2 [Short Answer]
What is double fertilisation? Write the chromosome numbers of the products. (2 marks)
Answer: Two fusions: (1) Syngamy — male gamete + egg = Zygote (2n). (2) Triple fusion —
2nd male gamete + 2 polar nuclei = Primary Endosperm Nucleus PEN (3n).
Explanation: Discovered by Nawaschin (1898). Unique to angiosperms. Zygote forms embryo; PEN
forms endosperm.
Board Tip: Always write 2n for zygote and 3n for PEN — examiner checks chromosome numbers
Q3 [Assertion-Reason]
A: Pollination and fertilisation are different events.
R: Pollination is transfer of pollen to stigma; fertilisation is fusion of gametes inside the ovule.
Options: (a) Both true, R explains A (b) Both true, R doesn't explain (c) A true R false (d) A false R
true
Answer: (a) Both A and R are true and R is the correct explanation.
Explanation: Pollination = pre-fertilisation event on stigma. Fertilisation = inside embryo sac. R correctly
explains A.
Q4 [MCQ]
The nutritive tissue formed after triple fusion in angiosperms is called:
Answer: Endosperm (3n — triploid)
Explanation: Endosperm is 3n, formed from PEN. In coconut, liquid endosperm = coconut water; solid =
copra.
CBSE Board Exam Preparation 2025-26 | Score 90%+
, CBSE CLASS 12 BIOLOGY — MOST IMPORTANT QUESTIONS Page 4
Q5 [Short Answer]
What is apomixis? Give one agricultural application. (2 marks)
Answer: Apomixis = production of seeds without fertilisation (asexual seed formation).
Application: Preserves superior hybrid traits — no need to buy hybrid seeds every year.
Seeds breed true.
Explanation: Found in Asteraceae and Gramineae. Apomixis + hybrid vigour = major advantage in crop
production.
Q6 [Short Answer]
Distinguish between self-pollination and cross-pollination. Give one example each. (3 marks)
Answer: Self-pollination: pollen from same flower/plant to its stigma. E.g., Wheat, Pea.
Cross-pollination: pollen from different plant of same species. E.g., Maize. Cross-pollination
promotes genetic variation and hybrid vigour.
Explanation: Adaptations for cross-pollination: Dichogamy, Herkogamy, Self-incompatibility, Dioecy.
Q7 [Case-Based]
Priya noticed some orchids mimic female insects — no nectar reward, yet get pollinated by male
bees.
(i) Name this pollination strategy.
(ii) Is this mutualism? Justify.
(iii) Name the pollinating agent.
Answer: (i) Deceptive/Floral mimicry pollination. (ii) No — only plant benefits, bee gets no
reward — one-sided. (iii) Insects (entomophily — bees).
Explanation: Reward-less flowers use deception. These test HOTS in case-based questions.
Q8 [Long Answer]
Describe the structure of a mature angiosperm embryo sac with a labelled diagram. (5 marks)
Answer: 7-celled, 8-nucleate: (1) Egg apparatus — 1 egg cell + 2 synergids (micropylar end).
(2) Central cell — 2 polar nuclei. (3) 3 antipodal cells (chalazal end). Synergids have filiform
apparatus. Polar nuclei fuse to form secondary nucleus.
Explanation: Diagram must label: egg cell, synergids, antipodals, central cell, polar nuclei, micropylar
end, chalazal end.
Board Tip: 7 cells, 8 nuclei — memorise this fact
Q9 [MCQ]
CBSE Board Exam Preparation 2025-26 | Score 90%+
