Exam-Oriented Biology MCQs for CBSE Class 12 Students

(Strictly NCERT-Based | Board-Focused | With Detailed Answers & Concept Explanations)

Section A: Reproduction (10 MCQs)

Q1. The surge of which hormone directly causes ovulation in human females?
A. FSH
B. Estrogen
C. LH
D. Progesterone

Answer: C. LH
Explanation: A sharp rise (LH surge) leads to rupture of the mature Graafian follicle and release of the ovum.

Q2. Double fertilization in flowering plants results in the formation of:
A. Zygote and nucellus
B. Embryo and perisperm
C. Zygote and endosperm
D. Embryo sac and endosperm

Answer: C. Zygote and endosperm
Explanation: One male gamete fuses with egg (syngamy) forming zygote, while the other fuses with polar nuclei forming endosperm.

Q3. The acrosome of sperm contains enzymes required for:
A. Sperm motility
B. Energy production
C. Penetration of ovum
D. Hormone secretion

Answer: C. Penetration of ovum
Explanation: Acrosomal enzymes help sperm penetrate the zona pellucida.

Q4. Which hormone maintains the uterine lining during pregnancy?
A. Estrogen
B. Oxytocin
C. Progesterone
D. Prolactin

Answer: C. Progesterone
Explanation: Progesterone prevents uterine contractions and maintains endometrium.

Q5. Apomixis is advantageous because it:
A. Produces genetic variation
B. Requires pollination
C. Maintains hybrid vigor
D. Produces sterile seeds

Answer: C. Maintains hybrid vigor
Explanation: Seeds formed without fertilization preserve desirable traits.

Q6. Implantation of embryo in humans occurs in the:
A. Ovary
B. Cervix
C. Fallopian tube
D. Uterus

Answer: D. Uterus
Explanation: The blastocyst embeds into the endometrium.

Q7. Menopause refers to:
A. First ovulation
B. First menstruation
C. Temporary stoppage of cycle
D. Permanent cessation of menstruation

Answer: D. Permanent cessation of menstruation
Explanation: It marks the end of reproductive phase in females.

Q8. Which part of coconut is consumed as food?
A. Embryo
B. Pericarp
C. Endosperm
D. Cotyledon

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

Q9. Which contraceptive method also provides protection from STDs?
A. IUD
B. Oral pills
C. Vasectomy
D. Condom

Answer: D. Condom
Explanation: Condoms act as barrier methods preventing infection transmission.

Q10. Placenta functions as:
A. Respiratory organ
B. Endocrine organ
C. Excretory organ
D. All of the above

Answer: D. All of the above
Explanation: Placenta exchanges gases, nutrients, wastes, and secretes hormones.

Section B: Genetics and Evolution (10 MCQs)

Q11. Mendel’s Law of Segregation states that:
A. Genes blend during inheritance
B. Alleles separate during gamete formation
C. Only dominant genes are inherited
D. Characters assort independently

Answer: B. Alleles separate during gamete formation
Explanation: Each gamete receives only one allele of a gene.

Q12. Which disorder is inherited as X-linked recessive?
A. Down syndrome
B. Hemophilia
C. Thalassemia
D. Phenylketonuria

Answer: B. Hemophilia
Explanation: Hemophilia affects males more due to X-linked inheritance.

Q13. DNA replication occurs during which phase of cell cycle?
A. G₁
B. S
C. G₂
D. M

Answer: B. S
Explanation: S-phase is the synthesis phase of interphase.

Q14. The start codon for translation is:
A. UAA
B. UAG
C. AUG
D. UGA

Answer: C. AUG
Explanation: AUG codes for methionine and initiates protein synthesis.

Q15. The unit of evolution is considered to be:
A. Individual
B. Species
C. Population
D. Ecosystem

Answer: C. Population
Explanation: Evolution involves changes in allele frequency within populations.

Q16. Homologous organs provide evidence for:
A. Convergent evolution
B. Parallel evolution
C. Divergent evolution
D. Co-evolution

Answer: C. Divergent evolution
Explanation: Same origin but different functions indicate divergence.

Q17. Crossing over takes place during:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diplotene

Answer: C. Pachytene
Explanation: Exchange of genetic material occurs between homologous chromosomes.

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

Answer: C. Small populations
Explanation: Random allele frequency changes are more significant in small populations.

Q19. RNA polymerase is required for:
A. DNA replication
B. Transcription
C. Translation
D. Mutation

Answer: B. Transcription
Explanation: It synthesizes RNA using DNA as template.

Q20. Darwin’s finches represent an example of:
A. Convergent evolution
B. Genetic drift
C. Adaptive radiation
D. Parallel evolution

Answer: C. Adaptive radiation
Explanation: Different species evolved from a common ancestor to occupy different niches.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Curd formation is due to the action of:
A. Yeast
B. Lactobacillus
C. Penicillium
D. Rhizobium

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

Q22. Malaria is caused by:
A. Virus
B. Bacterium
C. Protozoan
D. Fungus

Answer: C. Protozoan
Explanation: Caused by Plasmodium species.

Q23. Antibiotics are ineffective against:
A. Bacteria
B. Protozoa
C. Viruses
D. Fungi

Answer: C. Viruses
Explanation: Viruses lack metabolic pathways targeted by antibiotics.

Q24. Single Cell Protein (SCP) is mainly rich in:
A. Carbohydrates
B. Proteins
C. Lipids
D. Minerals

Answer: B. Proteins
Explanation: SCP provides high-quality protein.

Q25. AIDS is caused by:
A. Bacterium
B. Fungus
C. Virus
D. Protozoan

Answer: C. Virus
Explanation: Human Immunodeficiency Virus (HIV) attacks immune cells.

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

Answer: B. Methane
Explanation: Methane is the major fuel component.

Q27. Which organism acts as a biofertilizer?
A. Yeast
B. Azotobacter
C. Virus
D. Lactobacillus

Answer: B. Azotobacter
Explanation: It fixes atmospheric nitrogen in soil.

Q28. Penicillin is produced by:
A. Bacteria
B. Algae
C. Virus
D. Fungus

Answer: D. Fungus
Explanation: Produced by Penicillium species.

Q29. Sewage treatment plants mainly depend on:
A. Algae
B. Protozoa
C. Bacteria
D. Fungi

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

Q30. Rabies spreads mainly through:
A. Air
B. Water
C. Animal bite
D. Food

Answer: C. Animal bite
Explanation: Virus spreads through saliva of infected animals.

Section D: Biotechnology (10 MCQs)

Q31. Restriction enzymes are also known as:
A. Molecular glue
B. Molecular scissors
C. Vectors
D. Markers

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

Q32. PCR is a technique used for:
A. DNA sequencing
B. DNA amplification
C. Protein synthesis
D. Gene silencing

Answer: B. DNA amplification
Explanation: PCR produces millions of copies of DNA.

Q33. The heat-stable enzyme used in PCR is:
A. DNA ligase
B. Taq polymerase
C. RNA polymerase
D. Primase

Answer: B. Taq polymerase
Explanation: It remains active at high temperatures.

Q34. Bt cotton is resistant to:
A. Viruses
B. Fungi
C. Insects
D. Weeds

Answer: C. Insects
Explanation: Bt toxin kills insect larvae.

Q35. A commonly used cloning vector is:
A. Ribosome
B. Chromosome
C. Plasmid
D. mRNA

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

Q36. ELISA is based on:
A. DNA hybridization
B. Antigen–antibody interaction
C. RNA synthesis
D. Protein folding

Answer: B. Antigen–antibody interaction
Explanation: Used for disease diagnosis.

Q37. Recombinant human insulin is produced using:
A. Yeast
B. Virus
C. E. coli
D. Algae

Answer: C. E. coli
Explanation: Genetically engineered bacteria produce insulin.

Q38. RNA interference is used to:
A. Clone genes
B. Silence genes
C. Amplify DNA
D. Translate mRNA

Answer: B. Silence genes
Explanation: RNAi blocks mRNA translation.

Q39. A bioreactor provides:
A. Antibiotics
B. Genetic material
C. Optimal growth conditions
D. Enzymes only

Answer: C. Optimal growth conditions
Explanation: Controls pH, oxygen, nutrients, and temperature.

Q40. Selectable marker genes help in:
A. DNA cutting
B. Identifying recombinants
C. Replication
D. Transcription

Answer: B. Identifying recombinants
Explanation: They distinguish transformed cells.

Section E: Ecology and Environment (10 MCQs)

Q41. The ultimate source of energy in an ecosystem is:
A. Producers
B. Consumers
C. Decomposers
D. Sun

Answer: D. Sun
Explanation: Solar energy drives all ecosystem processes.

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

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

Q43. Which biogeochemical cycle has no gaseous phase?
A. Carbon
B. Nitrogen
C. Water
D. Phosphorus

Answer: D. Phosphorus
Explanation: Phosphorus circulates through rocks and soil.

Q44. Lichens are indicators of:
A. Water pollution
B. Soil fertility
C. Air pollution
D. Radiation

Answer: C. Air pollution
Explanation: Lichens are sensitive to sulfur dioxide.

Q45. The major cause of biodiversity loss is:
A. Pollution
B. Climate change
C. Habitat loss
D. Overpopulation

Answer: C. Habitat loss
Explanation: Destruction of natural habitats leads to extinction.

Q46. Biological magnification refers to:
A. Energy loss
B. Population increase
C. Accumulation of toxins
D. Nutrient cycling

Answer: C. Accumulation of toxins
Explanation: Toxins increase in concentration at higher trophic levels.

Q47. Eutrophication occurs due to excess of:
A. Oxygen
B. Nutrients
C. Heat
D. Salts

Answer: B. Nutrients
Explanation: Excess nitrates and phosphates cause algal blooms.

Q48. In-situ conservation includes:
A. Zoo
B. Seed bank
C. Botanical garden
D. National park

Answer: D. National park
Explanation: Conservation within natural habitat.

Q49. Ex-situ conservation includes:
A. Wildlife sanctuary
B. Biosphere reserve
C. National park
D. Zoological park

Answer: D. Zoological park
Explanation: Conservation outside natural habitat.

Q50. The term “ecosystem” was given by:
A. Odum
B. Clements
C. Darwin
D. Tansley

Answer: D. Tansley
Explanation: A.G. Tansley coined the term ecosystem.

✅ These exam-oriented, NCERT-aligned Biology MCQs are ideal for CBSE Class 12 students preparing for board exams.