High-Scoring MCQs for CBSE Class 12 Biology Exams

(NCERT-Based | Exam-Focused | With Answers & Concept-Clearing Explanations)

Section A: Reproduction (10 MCQs)

Q1. Which hormone is responsible for the maintenance of corpus luteum during early pregnancy?
A. LH
B. FSH
C. hCG
D. Progesterone

Answer: C. hCG
Explanation: Human chorionic gonadotropin (hCG), secreted by the embryo, maintains the corpus luteum to ensure continued progesterone secretion.

Q2. In angiosperms, triple fusion results in the formation of:
A. Diploid embryo
B. Haploid endosperm
C. Triploid endosperm
D. Diploid endosperm

Answer: C. Triploid endosperm
Explanation: One male gamete fuses with two polar nuclei, forming a triploid primary endosperm nucleus.

Q3. The acrosome of sperm is derived from:
A. Nucleus
B. Golgi apparatus
C. Mitochondria
D. Endoplasmic reticulum

Answer: B. Golgi apparatus
Explanation: The acrosome forms from Golgi vesicles and contains enzymes essential for fertilization.

Q4. Which of the following is a natural method of contraception?
A. Copper-T
B. Oral pills
C. Periodic abstinence
D. Vasectomy

Answer: C. Periodic abstinence
Explanation: Avoiding intercourse during fertile days reduces the chances of fertilization.

Q5. Menopause is characterized by:
A. Increase in estrogen
B. Permanent cessation of ovulation
C. Start of menstrual cycle
D. Increased fertility

Answer: B. Permanent cessation of ovulation
Explanation: Menopause marks the end of reproductive phase in females.

Q6. The edible part of coconut is:
A. Embryo
B. Perisperm
C. Endosperm
D. Cotyledon

Answer: C. Endosperm
Explanation: Coconut water (liquid) and kernel (solid) both represent endosperm.

Q7. Syngamy refers to:
A. Fusion of two polar nuclei
B. Fusion of male and female gametes
C. Transfer of pollen
D. Development of embryo

Answer: B. Fusion of male and female gametes
Explanation: Syngamy leads to zygote formation.

Q8. Which hormone stimulates spermatogenesis?
A. LH
B. FSH
C. Testosterone
D. Estrogen

Answer: B. FSH
Explanation: FSH acts on Sertoli cells to promote spermatogenesis.

Q9. Which plant shows cleistogamy?
A. Sunflower
B. Pea
C. Rice
D. Wheat

Answer: B. Pea
Explanation: Cleistogamous flowers remain closed and ensure self-pollination.

Q10. Implantation of embryo in humans occurs in the:
A. Ovary
B. Fallopian tube
C. Uterus
D. Cervix

Answer: C. Uterus
Explanation: The blastocyst embeds into the endometrium of the uterus.

Section B: Genetics and Evolution (10 MCQs)

Q11. The phenotypic ratio of incomplete dominance in F₂ generation is:
A. 3:1
B. 1:2:1
C. 9:3:3:1
D. 1:1

Answer: B. 1:2:1
Explanation: Heterozygotes show intermediate phenotype.

Q12. The genetic disorder caused due to absence of an enzyme is:
A. Down syndrome
B. Turner syndrome
C. Phenylketonuria
D. Klinefelter syndrome

Answer: C. Phenylketonuria
Explanation: Lack of phenylalanine hydroxylase leads to PKU.

Q13. Crossing over occurs during:
A. Pachytene
B. Zygotene
C. Diplotene
D. Leptotene

Answer: A. Pachytene
Explanation: Exchange of genetic material between homologous chromosomes occurs in pachytene stage.

Q14. The term “survival of the fittest” was given by:
A. Darwin
B. Wallace
C. Spencer
D. Mendel

Answer: C. Spencer
Explanation: Herbert Spencer coined the phrase to explain natural selection.

Q15. Which is a sex-linked disease?
A. Thalassemia
B. Sickle cell anemia
C. Hemophilia
D. Phenylketonuria

Answer: C. Hemophilia
Explanation: Hemophilia is an X-linked recessive disorder.

Q16. The function of tRNA is to:
A. Carry amino acids
B. Carry genetic code
C. Form ribosomes
D. Replicate DNA

Answer: A. Carry amino acids
Explanation: tRNA transports specific amino acids during protein synthesis.

Q17. Mutation causing loss of function of gene is called:
A. Silent mutation
B. Missense mutation
C. Nonsense mutation
D. Frameshift mutation

Answer: C. Nonsense mutation
Explanation: It introduces a premature stop codon.

Q18. Genetic drift is more prominent in:
A. Large populations
B. Stable populations
C. Small populations
D. Migrating populations

Answer: C. Small populations
Explanation: Random changes in allele frequency affect small populations more strongly.

Q19. RNA is synthesized in which direction?
A. 3′ → 5′
B. 5′ → 3′
C. 2′ → 3′
D. 1′ → 5′

Answer: B. 5′ → 3′
Explanation: RNA polymerase adds nucleotides at the 3′ end.

Q20. The correct sequence of evolutionary history is:
A. Fish → Amphibians → Reptiles → Birds
B. Amphibians → Fish → Reptiles → Birds
C. Reptiles → Fish → Amphibians → Birds
D. Fish → Reptiles → Amphibians → Birds

Answer: A. Fish → Amphibians → Reptiles → Birds
Explanation: This represents the evolutionary progression of vertebrates.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Which microorganism is used in yoghurt preparation?
A. Yeast
B. Lactobacillus
C. Streptococcus
D. Penicillium

Answer: B. Lactobacillus
Explanation: It converts milk lactose into lactic acid.

Q22. Which disease is spread by female Anopheles mosquito?
A. Dengue
B. Filariasis
C. Malaria
D. Chikungunya

Answer: C. Malaria
Explanation: Female Anopheles transmits Plasmodium parasite.

Q23. Which antibiotic inhibits bacterial cell wall synthesis?
A. Penicillin
B. Tetracycline
C. Chloramphenicol
D. Streptomycin

Answer: A. Penicillin
Explanation: Penicillin blocks peptidoglycan formation.

Q24. Biocontrol agents include:
A. Chemical fertilizers
B. Pathogens
C. Predators
D. Antibiotics

Answer: C. Predators
Explanation: Predators help control pests naturally.

Q25. The major source of antibiotics is:
A. Algae
B. Fungi
C. Protozoa
D. Viruses

Answer: B. Fungi
Explanation: Many antibiotics are derived from fungi.

Q26. Which disease is caused by HIV?
A. Cancer
B. Tuberculosis
C. AIDS
D. Hepatitis

Answer: C. AIDS
Explanation: HIV attacks the immune system causing AIDS.

Q27. SCP helps to solve:
A. Energy crisis
B. Protein deficiency
C. Water scarcity
D. Soil erosion

Answer: B. Protein deficiency
Explanation: SCP provides alternative protein source.

Q28. Which organism is used in sewage treatment?
A. Algae
B. Fungi
C. Bacteria
D. Protozoa

Answer: C. Bacteria
Explanation: Bacteria decompose organic matter.

Q29. Which vaccine provides passive immunity?
A. BCG
B. DPT
C. Antiserum
D. OPV

Answer: C. Antiserum
Explanation: Ready-made antibodies give immediate protection.

Q30. Which disease is zoonotic?
A. Typhoid
B. AIDS
C. Rabies
D. Malaria

Answer: C. Rabies
Explanation: Rabies is transmitted from animals to humans.

Section D: Biotechnology (10 MCQs)

Q31. The enzyme used to cut DNA is:
A. Ligase
B. Polymerase
C. Restriction endonuclease
D. Primase

Answer: C. Restriction endonuclease
Explanation: It cleaves DNA at specific recognition sites.

Q32. The first transgenic plant was:
A. Rice
B. Tobacco
C. Cotton
D. Wheat

Answer: B. Tobacco
Explanation: Tobacco was the first genetically modified plant.

Q33. Which vector is commonly used in gene cloning?
A. Plasmid
B. Ribosome
C. mRNA
D. tRNA

Answer: A. Plasmid
Explanation: Plasmids replicate independently in host cells.

Q34. ELISA is used for:
A. DNA sequencing
B. Disease diagnosis
C. Gene cloning
D. PCR

Answer: B. Disease diagnosis
Explanation: ELISA detects antigen–antibody interactions.

Q35. Bt toxin is effective against:
A. Bacteria
B. Viruses
C. Insects
D. Fungi

Answer: C. Insects
Explanation: Bt toxin disrupts insect gut epithelium.

Q36. Which technique separates proteins?
A. PCR
B. Chromatography
C. Gel electrophoresis
D. Blotting

Answer: C. Gel electrophoresis
Explanation: Proteins and nucleic acids are separated by size.

Q37. The selectable marker helps in:
A. DNA replication
B. Identifying recombinants
C. Protein synthesis
D. Transcription

Answer: B. Identifying recombinants
Explanation: Marker genes help select transformed cells.

Q38. Which hormone is produced by genetically engineered bacteria?
A. Insulin
B. Thyroxine
C. Estrogen
D. Adrenaline

Answer: A. Insulin
Explanation: Recombinant insulin is produced using bacteria.

Q39. RNA interference is used to:
A. Express genes
B. Amplify DNA
C. Silence genes
D. Mutate DNA

Answer: C. Silence genes
Explanation: RNAi blocks translation of target mRNA.

Q40. Bioreactors provide:
A. Sterile conditions
B. Optimal growth conditions
C. Genetic material
D. Enzymes

Answer: B. Optimal growth conditions
Explanation: They maintain temperature, pH, and nutrients.

Section E: Ecology and Environment (10 MCQs)

Q41. The major driving force of ecosystem is:
A. Producers
B. Consumers
C. Decomposers
D. Sunlight

Answer: D. Sunlight
Explanation: Solar energy supports all trophic levels.

Q42. Which biome has highest biodiversity?
A. Desert
B. Tundra
C. Tropical rainforest
D. Grassland

Answer: C. Tropical rainforest
Explanation: Warm and humid climate supports diverse life.

Q43. Decomposers belong to which trophic level?
A. First
B. Second
C. Third
D. All levels

Answer: D. All levels
Explanation: Decomposers act on dead matter from all trophic levels.

Q44. Greenhouse effect leads to:
A. Acid rain
B. Ozone depletion
C. Global warming
D. Eutrophication

Answer: C. Global warming
Explanation: Greenhouse gases trap heat.

Q45. The major source of atmospheric nitrogen fixation is:
A. Lightning
B. Industries
C. Bacteria
D. Algae

Answer: C. Bacteria
Explanation: Nitrogen-fixing bacteria convert N₂ to usable forms.

Q46. Which is a renewable resource?
A. Coal
B. Petroleum
C. Solar energy
D. Natural gas

Answer: C. Solar energy
Explanation: Solar energy is inexhaustible.

Q47. Lichens indicate:
A. Water purity
B. Soil fertility
C. Air quality
D. Climate change

Answer: C. Air quality
Explanation: Lichens are sensitive to air pollutants.

Q48. Biological magnification refers to:
A. Increase in population
B. Accumulation of toxins
C. Energy flow
D. Nutrient cycling

Answer: B. Accumulation of toxins
Explanation: Toxic substances increase at higher trophic levels.

Q49. Which is an ex-situ conservation method?
A. Wildlife sanctuary
B. National park
C. Seed bank
D. Biosphere reserve

Answer: C. Seed bank
Explanation: Conservation outside natural habitat.

Q50. The term ecosystem was coined by:
A. Odum
B. Tansley
C. Darwin
D. Haeckel

Answer: B. Tansley
Explanation: A.G. Tansley introduced the term ecosystem.

✅ These high-scoring MCQs strictly follow the NCERT syllabus and are ideal for CBSE Class 12 Biology board exam preparation.