CBSE Class 12 Biology Important MCQs with Answers

CBSE Class 12 Biology syllabus is vast, but scoring high becomes easy when you focus on high-weightage topics like Genetics, Ecology, Reproduction, and Biotechnology. With MCQs gaining importance in the board exam pattern, practicing concept-based multiple choice questions is no longer optional—it's essential. This short guide brings you chapter-wise important topics and carefully selected MCQs with answers, helping you revise faster and avoid common exam mistakes.

Multiple Choice Questions have become the backbone of the CBSE Class 12 Biology paper. With the latest exam pattern carrying 30–40% weightage for MCQs, mastering them chapter-by-chapter is no longer optional — it's essential for scoring 90+.

👉 Most students repeat the same easy questions over and over

👉 No proper explanations for wrong answers

👉 No way to track which chapters are truly mastered

CBSE Class 12 Biology has 13 chapters across 5 units. The board allocates marks unevenly — some chapters carry far higher MCQ probability. Practicing chapter-wise helps you focus on weak areas, understand question patterns, and build confidence unit by unit.

Below you'll find the most high-yield MCQ topics per chapter and 2–3 important MCQs with full explanations — based on CBSE past papers and the latest syllabus.

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Unit 1

Reproduction (Chapters 1–3)

01

Sexual Reproduction in Flowering Plants

High yieldNEET

High-yield MCQ topics

  • Structure of anther and ovule
  • Microsporogenesis vs Megasporogenesis
  • Double fertilization & triple fusion
  • Endosperm formation (nuclear vs cellular)
  • Apomixis and polyembryony

Important MCQs

MCQ 1Which cells of the embryo sac degenerate after fertilization?
(a) Antipodals only (b) Synergids only (c) Both antipodals and synergids (d) Egg cell

Answer: (c)

After fertilization, both synergids (which guided pollen tube entry) and antipodal cells degenerate as they are no longer needed. The egg cell forms the embryo, central cell forms endosperm.

⚠️ Students often choose only synergids, forgetting that antipodals also degenerate post-fertilization.
MCQ 2In angiosperms, triple fusion involves the fusion of:
(a) Two polar nuclei + one male gamete (b) One polar nucleus + two male gametes (c) Egg cell + one male gamete + polar nucleus (d) Two synergids + one male gamete

Answer: (a)

Triple fusion = 2 polar nuclei + 1 male gamete → primary endosperm nucleus (3n). Distinct from syngamy, together they form double fertilization.

⚠️ Confusing triple fusion with double fertilization is a common error. Double fertilization includes both syngamy and triple fusion.
MCQ 3Megasporogenesis results in the formation of:
(a) Four haploid megaspores (b) One diploid functional megaspore (c) Eight-nucleate embryo sac directly (d) Microspore mother cell

Answer: (a)

Megaspore mother cell (MMC) undergoes meiosis to produce a linear tetrad of 4 haploid megaspores. Only one functional megaspore develops further.

⚠️ Students sometimes jump directly to the embryo sac, but megasporogenesis ends with 4 megaspores.
02

Human Reproduction

High yieldNEET

High-yield MCQ topics

  • Spermatogenesis & oogenesis stages
  • Menstrual cycle phases
  • Fertilization & implantation
  • Placenta structure and functions

Important MCQs

MCQ 1Which hormone triggers ovulation?
(a) FSH(b) Progesterone(c) LH surge(d) Estrogen

Answer: (c)

LH surge around day 14 triggers release of secondary oocyte. FSH stimulates follicle growth; estrogen peaks before LH surge.

⚠️ Many say FSH, but ovulation is specifically caused by LH surge.
MCQ 2Implantation occurs in which layer of the uterus?
(a) Myometrium(b) Perimetrium(c) Endometrium(d) Peritoneum

Answer: (c)

Endometrium is the innermost lining where blastocyst implants. Myometrium is muscular layer.

⚠️ Myometrium is often confused with endometrium – remember endo = inner.
03

Reproductive Health

Board priority

High-yield MCQ topics

  • Contraceptive methods (barrier, IUD, pills)
  • STDs & causative organisms
  • MTP, ART: IVF, ZIFT, GIFT
MCQ 1ZIFT stands for:
(a) Zygote Intra-Fallopian Transfer(b) Zygote In-vitro Fertilization Transfer(c) Zygote Internal Female Transfer(d) Zonal Internal Fertilization Technique

Answer: (a)

Zygote is transferred into fallopian tube. IVF-ET transfers embryo into uterus.

⚠️ ZIFT vs IVF: site of transfer differs – fallopian tube vs uterus.
MCQ 2Which contraceptive method also provides protection against STDs?
(a) Oral pills(b) Copper-T(c) Condoms(d) Diaphragm alone

Answer: (c)

Condoms are the only contraceptives offering dual protection: pregnancy + STDs.

⚠️ Diaphragm does NOT prevent STDs; only condoms do.

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Unit 2

Genetics & Evolution (Chapters 4–6)

04

Principles of Inheritance & Variation

High yield
  • Mendel's laws & ratios
  • Incomplete dominance, codominance
  • ABO blood groups
  • Chromosomal disorders
A person with blood group AB has genotype:
(a) IAIB(b) IAi(c) IBi(d) ii

Answer: (a)

AB shows codominance, both A and B alleles expressed.

⚠️ Codominance ≠ incomplete dominance.
Turner's syndrome is caused by:
(a) Trisomy 21(b) XXY(c) 45, XO(d) XYY

Answer: (c)

Monosomy of X chromosome, female with short stature, webbed neck.

⚠️ Turner XO vs Klinefelter XXY – classic confusion.
05

Molecular Basis of Inheritance

NEET essential
  • DNA replication enzymes
  • Transcription & genetic code
  • Lac operon
Enzyme that joins Okazaki fragments on lagging strand:
(a) DNA polymerase I(b) DNA ligase(c) Helicase(d) Primase

Answer: (b)

DNA ligase seals nicks between Okazaki fragments.

⚠️ Polymerase I fills gaps but does not seal – ligase does final joining.
In lac operon, repressor becomes inactive when:
(c) Allolactose binds to repressor(a) Glucose present(b) Lactose absent(d) RNA polymerase binds promoter

Answer: (c)

Allolactose (inducer) binds repressor, removes it from operator.

⚠️ Lactose itself is not the direct inducer – it's allolactose.
06

Evolution

Board priority
  • Evidences of evolution
  • Hardy-Weinberg principle
  • Adaptive radiation
Darwin's finches are an example of:
(b) Adaptive radiation(a) Convergent evolution(c) Industrial melanism(d) Founder effect

Answer: (b)

One ancestral species diversified into multiple ecological niches.

⚠️ Adaptive radiation is divergence from common ancestor, not convergent evolution.
Unit 3

Biology in Human Welfare (Chapters 7–8)

07

Human Health and Disease

High yield
  • Innate & acquired immunity
  • Lymphoid organs
  • Pathogens & diseases
  • Drugs & alcohol abuse
Which antibody is the first to appear during an immune response?
(a) IgG(b) IgM(c) IgA(d) IgE

Answer: (b)

IgM is the first immunoglobulin produced in primary response, later replaced by IgG.

⚠️ Many assume IgG is first, but IgM is the initial responder.
Malaria is caused by:
(a) Plasmodium(b) Entamoeba(c) Salmonella(d) Wuchereria

Answer: (a)

Plasmodium (protozoan) transmitted by Anopheles mosquito.

⚠️ Confusion with amoebiasis (Entamoeba) is common.
08

Microbes in Human Welfare

Board
  • Household products (curd, bread)
  • Industrial production (antibiotics, biofertilizers)
  • Sewage treatment & biogas
Which bacterium is used for curd formation?
(a) Lactobacillus(a) Lactobacillus(b) Streptococcus(c) Bacillus(d) Rhizobium

Answer: Lactobacillus

Lactobacillus converts milk to curd by producing lactic acid.

⚠️ Remember: curd = lactobacillus; acetic acid bacteria for vinegar.
⚡ Check Important Topics & MCQs for Physics →
Unit 4

Biotechnology (Chapters 9–10)

09

Biotechnology: Principles and Processes

NEET
  • Restriction enzymes & vectors
  • PCR, gel electrophoresis
  • Competent host preparation
The first restriction endonuclease isolated was:
(a) Hind II(b) EcoRI(c) BamHI(d) SalI

Answer: (a)

Hind II was the first restriction enzyme discovered. EcoRI is more commonly used but not the first.

⚠️ EcoRI is famous but Hind II holds historical first discovery.
10

Biotechnology and its Applications

  • GM crops (Bt cotton, golden rice)
  • Gene therapy, molecular diagnosis
  • Bioremediation
RNA interference (RNAi) is used to prevent:
(a) Viral infection in bacteria(b) Nematode infestation in plants(c) Bacterial blight in rice(d) Fungal rot in wheat

Answer: (b)

RNAi silences specific genes; used in plants against nematode Meloidogyne incognita.

⚠️ Connection: RNAi → nematode resistance in plants (CBSE special).
Unit 5

Ecology & Environment (Chapters 11–13)

11

Organisms and Populations

Board
  • Population attributes (density, natality)
  • Growth models (exponential/logistic)
  • Population interactions (mutualism, competition)
Carrying capacity (K) in a logistic growth curve refers to:
(a) Maximum population an environment can support(b) Maximum growth rate(c) Population at which growth is highest(d) Intrinsic rate of increase

Answer: (a)

K is the upper asymptote; the population stabilizes near K due to resource limits.

⚠️ Don't confuse K with r (intrinsic growth rate) or inflection point.
12

Ecosystem

  • Primary productivity, decomposition
  • Energy flow (10% law)
  • Ecological pyramids
According to Lindeman's 10% law, how much energy is transferred to next trophic level?
(a) 10%(b) 20%(c) 1%(d) 50%

Answer: (a)

Only about 10% of energy flows from one trophic level to the next; rest lost as heat.

⚠️ Misremembering as 20% or 30% – stick to 10% law for boards.
13

Biodiversity and Conservation

High yield
  • Species diversity patterns (latitudinal gradient)
  • Biodiversity loss & IUCN Red List
  • In-situ & ex-situ conservation
Which one is an example of in-situ conservation?
(a) Biosphere reserve(b) Botanical garden(c) Seed bank(d) Zoo

Answer: (a)

In-situ = within natural habitat; biosphere reserves, national parks. Ex-situ = zoos, botanical gardens.

⚠️ Zoos/Botanical gardens are ex-situ, not in-situ.

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Pro tips to master Class 12 Biology MCQs

StrategyHow to apply
Daily 20-minute drillUse your free 20 MCQs every 48 hours. Solve 10 MCQs a day — quota never expires.
Chapter-by-chapter masteryStart with a challenging chapter, practice until platform shows "no unseen questions left".
Mistake journalRead "common mistake" notes after each MCQ. Write it down. You'll stop repeating errors.
Refer friends for more practiceShare unique referral link. Each friend gives 30 bonus MCQs — stackable.
Switch to Advanced for NEETSolve Preparatory level then Advanced for the same chapter.

Frequently asked questions

Is mcqadda.in free to use?

Yes — you get 20 free MCQs on signup. Your quota resets to 20 every 48 hours, and unused questions carry forward. You also earn unlimited bonus MCQs by referring friends (30 MCQs per referral).

Can I practise only one chapter at a time?

Absolutely. Choose any chapter from the Class 12 Biology list. The system tracks progress per chapter independently.

Does it follow the latest CBSE syllabus?

Yes, strictly follows NCERT Class 12 Biology (2026-27) with all 13 chapters.

Can I use it on my phone?

Yes, mobile-friendly — no app needed.

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