Exam-Focused MCQs for CBSE Class 12 Biology (NCERT Based)

These 50 MCQs with answers and detailed explanations are strictly prepared as per the NCERT syllabus and CBSE board exam pattern. The questions are exam-focused, concept-driven, and high-yield, covering all major units of CBSE Class 12 Biology.
Each section aligns with frequently tested board-level concepts and competitive exam expectations.

Section A: Reproduction in Organisms (MCQs 1–10)

Q1. The acrosome of human sperm contains enzymes essential for:
A. Motility of sperm
B. Penetration of zona pellucida
C. Nourishment of ovum
D. Formation of zygote

Answer: B
Explanation: The acrosome contains hydrolytic enzymes like hyaluronidase and acrosin that help the sperm penetrate the zona pellucida of the ovum during fertilisation.

Q2. In humans, implantation of the blastocyst normally occurs in the:
A. Ovary
B. Cervix
C. Fallopian tube
D. Endometrium of uterus

Answer: D
Explanation: Implantation takes place in the thick, vascular endometrium of the uterus, which supports embryonic development.

Q3. Which hormone is responsible for maintenance of pregnancy?
A. Estrogen
B. FSH
C. Progesterone
D. LH

Answer: C
Explanation: Progesterone maintains uterine lining, prevents uterine contractions, and supports pregnancy.

Q4. Menstrual cycle is regulated by hormones from:
A. Hypothalamus only
B. Pituitary and ovary
C. Thyroid gland
D. Adrenal cortex

Answer: B
Explanation: FSH and LH from pituitary and estrogen and progesterone from ovaries regulate the menstrual cycle.

Q5. The process of formation of male gametes is called:
A. Oogenesis
B. Spermiogenesis
C. Spermatogenesis
D. Gametogenesis

Answer: C
Explanation: Spermatogenesis involves formation of sperm from spermatogonia in seminiferous tubules.

Q6. Which structure prevents polyspermy?
A. Corona radiata
B. Zona pellucida
C. Acrosome
D. Nucleus

Answer: B
Explanation: Zona pellucida hardens after fertilisation, preventing entry of additional sperms.

Q7. Human chorionic gonadotropin (hCG) is secreted by:
A. Ovary
B. Placenta
C. Pituitary
D. Endometrium

Answer: B
Explanation: hCG is secreted by trophoblastic cells of the placenta and maintains corpus luteum.

Q8. Which stage of embryo is implanted in uterus?
A. Morula
B. Zygote
C. Blastocyst
D. Gastrula

Answer: C
Explanation: Implantation occurs at the blastocyst stage.

Q9. Amniotic fluid functions in:
A. Nutrition
B. Excretion
C. Protection from shocks
D. Hormone secretion

Answer: C
Explanation: Amniotic fluid cushions the embryo and protects it from mechanical injury.

Q10. Placenta acts as an endocrine organ by secreting:
A. Insulin
B. Thyroxine
C. hCG and progesterone
D. Adrenaline

Answer: C
Explanation: Placenta secretes hormones essential for maintaining pregnancy.

Section B: Genetics and Evolution (MCQs 11–20)

Q11. Mendel’s law of segregation is based on:
A. Independent assortment
B. Allele separation during gamete formation
C. Dominance
D. Gene interaction

Answer: B
Explanation: During gametogenesis, alleles separate so each gamete carries only one allele.

Q12. A test cross is performed to determine:
A. Dominant genotype
B. Recessive phenotype
C. Genotype of dominant individual
D. Mutation

Answer: C
Explanation: Test cross reveals whether a dominant phenotype is homozygous or heterozygous.

Q13. Phenotypic ratio in Mendelian monohybrid cross is:
A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 2:1

Answer: C
Explanation: Dominant trait appears three times more than recessive in F₂ generation.

Q14. DNA replication occurs during:
A. G₁ phase
B. S phase
C. G₂ phase
D. M phase

Answer: B
Explanation: S phase is synthesis phase where DNA is replicated.

Q15. The genetic material in most organisms is:
A. RNA
B. Protein
C. DNA
D. Lipid

Answer: C
Explanation: DNA stores and transmits genetic information.

Q16. Transcription occurs in:
A. Ribosome
B. Cytoplasm
C. Nucleus
D. Golgi apparatus

Answer: C
Explanation: DNA-dependent RNA synthesis occurs in nucleus.

Q17. Codon is a sequence of:
A. Two nucleotides
B. Three nucleotides
C. Four nucleotides
D. Five nucleotides

Answer: B
Explanation: Each codon consists of three nucleotides coding for one amino acid.

Q18. Mutation refers to:
A. Gene expression
B. DNA repair
C. Sudden heritable change
D. Crossing over

Answer: C
Explanation: Mutation causes permanent change in DNA sequence.

Q19. Hardy-Weinberg principle relates to:
A. Genetic drift
B. Population genetics
C. Natural selection
D. Mutation rate

Answer: B
Explanation: It explains genetic equilibrium in a population.

Q20. Evolutionary fitness refers to:
A. Strength
B. Longevity
C. Reproductive success
D. Body size

Answer: C
Explanation: Fitness is measured by ability to produce viable offspring.

Section C: Biology and Human Welfare (MCQs 21–30)

Q21. Antibiotics are effective against:
A. Viruses
B. Protozoa
C. Bacteria
D. Fungi

Answer: C
Explanation: Antibiotics target bacterial metabolic pathways.

Q22. Which organism produces penicillin?
A. Rhizopus
B. Penicillium
C. Aspergillus
D. Saccharomyces

Answer: B
Explanation: Penicillin is produced by Penicillium notatum.

Q23. Vaccination works on principle of:
A. Passive immunity
B. Active immunity
C. Natural immunity
D. Autoimmunity

Answer: B
Explanation: Vaccines stimulate immune system to produce antibodies.

Q24. Which disease is caused by virus?
A. Tuberculosis
B. Typhoid
C. AIDS
D. Malaria

Answer: C
Explanation: AIDS is caused by HIV, a retrovirus.

Q25. Biofertilisers increase soil fertility by:
A. Killing pathogens
B. Fixing atmospheric nitrogen
C. Providing hormones
D. Removing toxins

Answer: B
Explanation: Biofertilisers like Rhizobium fix nitrogen biologically.

Q26. Biogas mainly contains:
A. CO₂
B. Methane
C. Oxygen
D. Nitrogen

Answer: B
Explanation: Methane is the major combustible component of biogas.

Q27. Which microbe is used in sewage treatment?
A. Virus
B. Algae
C. Bacteria
D. Protozoa

Answer: C
Explanation: Bacteria degrade organic matter in sewage.

Q28. Single cell protein is rich in:
A. Fats
B. Vitamins
C. Proteins
D. Minerals

Answer: C
Explanation: SCP provides high-quality protein.

Q29. Mycorrhiza is an association between:
A. Algae and fungi
B. Fungi and roots
C. Bacteria and roots
D. Virus and plant

Answer: B
Explanation: Mycorrhiza enhances nutrient absorption in plants.

Q30. Which disease spreads by mosquito vector?
A. Cholera
B. Malaria
C. Typhoid
D. Pneumonia

Answer: B
Explanation: Malaria is transmitted by female Anopheles mosquito.

Section D: Biotechnology and Its Applications (MCQs 31–40)

Q31. Restriction enzymes are also called:
A. Ligases
B. Molecular scissors
C. Polymerases
D. Vectors

Answer: B
Explanation: They cut DNA at specific recognition sites.

Q32. Plasmids are commonly found in:
A. Virus
B. Bacteria
C. Fungi
D. Algae

Answer: B
Explanation: Plasmids are circular extra-chromosomal DNA in bacteria.

Q33. PCR is used for:
A. DNA sequencing
B. DNA amplification
C. DNA repair
D. Transcription

Answer: B
Explanation: PCR amplifies a specific DNA segment.

Q34. Insulin used by diabetics is produced by:
A. Animal pancreas
B. Recombinant DNA technology
C. Chemical synthesis
D. Plant extracts

Answer: B
Explanation: Human insulin is produced using genetically modified bacteria.

Q35. Vector in genetic engineering acts as:
A. Enzyme
B. Host
C. Carrier of gene
D. Protein

Answer: C
Explanation: Vectors transfer desired gene into host cell.

Q36. Bt cotton is resistant to:
A. Virus
B. Weed
C. Insect pests
D. Fungi

Answer: C
Explanation: Bt gene produces toxin lethal to insect larvae.

Q37. Gene therapy aims to:
A. Kill microbes
B. Replace defective genes
C. Prevent mutation
D. Clone humans

Answer: B
Explanation: Gene therapy corrects genetic disorders.

Q38. ELISA test is used for diagnosis of:
A. Cancer
B. AIDS
C. Tuberculosis
D. Malaria

Answer: B
Explanation: ELISA detects HIV antibodies.

Q39. Recombinant DNA is formed by:
A. Transcription
B. Translation
C. Ligation
D. Mutation

Answer: C
Explanation: DNA fragments are joined using ligase enzyme.

Q40. Transgenic organisms contain:
A. Foreign DNA
B. Extra chromosomes
C. Mutated DNA
D. Deleted genes

Answer: A
Explanation: Transgenic organisms possess genes from other species.

Section E: Ecology and Environment (MCQs 41–50)

Q41. Primary producers are:
A. Carnivores
B. Herbivores
C. Autotrophs
D. Decomposers

Answer: C
Explanation: Autotrophs synthesize food using sunlight.

Q42. Pyramid of energy is always:
A. Inverted
B. Upright
C. Spindle-shaped
D. Irregular

Answer: B
Explanation: Energy decreases at each trophic level.

Q43. Ozone depletion is caused by:
A. CO₂
B. SO₂
C. CFCs
D. Methane

Answer: C
Explanation: CFCs release chlorine radicals that destroy ozone.

Q44. Biodiversity hotspot is characterised by:
A. Low species richness
B. High endemism
C. Low population
D. Cold climate

Answer: B
Explanation: Hotspots have high species diversity and endemism.

Q45. Greenhouse effect leads to:
A. Cooling
B. Global warming
C. Ozone formation
D. Acid rain

Answer: B
Explanation: Trapping of heat causes global temperature rise.

Q46. Decomposers belong to:
A. First trophic level
B. Second trophic level
C. Last trophic level
D. Producers

Answer: C
Explanation: Decomposers recycle nutrients from dead organisms.

Q47. Which gas is major contributor to greenhouse effect?
A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Helium

Answer: C
Explanation: CO₂ traps infrared radiation.

Q48. Ecological succession ending in stable community is called:
A. Primary succession
B. Secondary succession
C. Climax community
D. Pioneer stage

Answer: C
Explanation: Climax community is stable and self-sustaining.

Q49. Which biome has highest biodiversity?
A. Desert
B. Tundra
C. Tropical rainforest
D. Grassland

Answer: C
Explanation: Tropical rainforests support maximum species diversity.

Q50. Conservation within natural habitat is called:
A. Ex situ conservation
B. In situ conservation
C. Cryopreservation
D. Artificial selection

Answer: B
Explanation: In situ conservation protects species in their natural ecosystems.