CBSE Class 12 Biology MCQs for Board Exam Preparation

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

Section A: Reproduction (10 MCQs)

Q1. Which hormone is responsible for ovulation in humans?
A. FSH
B. LH
C. Estrogen
D. Progesterone

Answer: B. LH
Explanation: A surge in Luteinizing Hormone (LH) triggers ovulation by causing rupture of the Graafian follicle and release of the ovum from the ovary.

Q2. In flowering plants, double fertilization results in the formation of:
A. Zygote and antipodal cells
B. Zygote and endosperm
C. Embryo and synergids
D. Endosperm and nucellus

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

Q3. The site of fertilization in humans is:
A. Ovary
B. Uterus
C. Cervix
D. Ampulla of fallopian tube

Answer: D. Ampulla of fallopian tube
Explanation: Fertilization usually occurs in the ampullary–isthmic junction of the fallopian tube.

Q4. Which structure prevents polyspermy in humans?
A. Corona radiata
B. Zona pellucida
C. Acrosome
D. Vitelline membrane

Answer: B. Zona pellucida
Explanation: After fertilization, the zona pellucida undergoes changes that block entry of additional sperms.

Q5. Apomixis refers to:
A. Sexual reproduction without fertilization
B. Asexual seed formation
C. Fusion of gametes
D. Vegetative reproduction

Answer: B. Asexual seed formation
Explanation: In apomixis, seeds are produced without fertilization, common in some grasses.

Q6. The function of seminal vesicles is to:
A. Produce sperms
B. Store sperms
C. Provide fructose-rich fluid
D. Secrete testosterone

Answer: C. Provide fructose-rich fluid
Explanation: Seminal vesicles secrete fructose which provides energy for sperm motility.

Q7. Which hormone maintains pregnancy?
A. Estrogen
B. Oxytocin
C. Progesterone
D. LH

Answer: C. Progesterone
Explanation: Progesterone maintains the uterine lining for implantation and pregnancy.

Q8. The transfer of pollen grains from anther to stigma is called:
A. Fertilization
B. Pollination
C. Germination
D. Syngamy

Answer: B. Pollination
Explanation: Pollination precedes fertilization and may occur via wind, water, or animals.

Q9. Which method of contraception is irreversible?
A. Condom
B. Oral pills
C. Vasectomy
D. IUD

Answer: C. Vasectomy
Explanation: Vasectomy involves cutting and tying the vas deferens, preventing sperm transport permanently.

Q10. Menarche refers to:
A. Cessation of menstruation
B. First ovulation
C. First menstruation
D. Menstrual cycle

Answer: C. First menstruation
Explanation: Menarche marks the beginning of reproductive life in human females.

Section B: Genetics and Evolution (10 MCQs)

Q11. Mendel’s Law of Segregation is based on:
A. Monohybrid cross
B. Dihybrid cross
C. Test cross
D. Back cross

Answer: A. Monohybrid cross
Explanation: The law states that alleles separate during gamete formation, evident from monohybrid ratios.

Q12. Which genotype represents a carrier of haemophilia?
A. XʰXʰ
B. XHXH
C. XHXʰ
D. XʰY

Answer: C. XHXʰ
Explanation: Carrier females possess one normal and one affected X chromosome.

Q13. The phenomenon where one gene influences multiple traits is called:
A. Polygenic inheritance
B. Pleiotropy
C. Codominance
D. Incomplete dominance

Answer: B. Pleiotropy
Explanation: A single gene affects multiple phenotypic traits, e.g., phenylketonuria.

Q14. DNA replication is:
A. Conservative
B. Dispersive
C. Semiconservative
D. Random

Answer: C. Semiconservative
Explanation: Each new DNA molecule has one parental and one newly synthesized strand.

Q15. The unit of evolution is:
A. Individual
B. Species
C. Population
D. Community

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

Q16. Hardy–Weinberg equilibrium is disturbed by all except:
A. Mutation
B. Migration
C. Random mating
D. Natural selection

Answer: C. Random mating
Explanation: Random mating helps maintain genetic equilibrium.

Q17. Which enzyme synthesizes RNA from DNA template?
A. DNA polymerase
B. RNA polymerase
C. Ligase
D. Restriction enzyme

Answer: B. RNA polymerase
Explanation: RNA polymerase catalyzes transcription.

Q18. Genetic material in most viruses is:
A. Protein
B. DNA only
C. RNA only
D. DNA or RNA

Answer: D. DNA or RNA
Explanation: Viruses may contain either DNA or RNA, but never both.

Q19. Homologous chromosomes separate during:
A. Meiosis I
B. Meiosis II
C. Mitosis
D. Interphase

Answer: A. Meiosis I
Explanation: Reduction division occurs when homologous chromosomes separate.

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

Answer: A. Adaptive radiation
Explanation: Finches evolved from a common ancestor into multiple species adapted to different niches.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Which microbe produces penicillin?
A. Rhizobium
B. Penicillium
C. Streptococcus
D. Lactobacillus

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

Q22. The causative agent of malaria is:
A. Virus
B. Bacteria
C. Protozoan
D. Fungus

Answer: C. Protozoan
Explanation: Malaria is caused by Plasmodium, a protozoan parasite.

Q23. Which vaccine is a killed vaccine?
A. BCG
B. OPV
C. IPV
D. MMR

Answer: C. IPV
Explanation: Inactivated Polio Vaccine contains killed virus.

Q24. Biogas mainly consists of:
A. CO₂
B. Methane
C. Hydrogen
D. Nitrogen

Answer: B. Methane
Explanation: Methane is the major component and fuel in biogas.

Q25. Which organism is used in cheese production?
A. Yeast
B. Penicillium
C. Lactobacillus
D. Aspergillus

Answer: B. Penicillium
Explanation: Certain cheeses use Penicillium species for flavor and texture.

Q26. Antibiotics are ineffective against:
A. Bacteria
B. Fungi
C. Viruses
D. Protozoa

Answer: C. Viruses
Explanation: Antibiotics target bacterial metabolism, not viral replication.

Q27. SCP refers to:
A. Single Cell Protein
B. Secondary Crop Production
C. Synthetic Chemical Protein
D. Stored Cell Product

Answer: A. Single Cell Protein
Explanation: SCP provides protein-rich biomass from microbes.

Q28. Which disease is caused by a bacterium?
A. AIDS
B. Typhoid
C. Malaria
D. Ringworm

Answer: B. Typhoid
Explanation: Typhoid is caused by Salmonella typhi.

Q29. Mycorrhiza shows a relationship of:
A. Parasitism
B. Commensalism
C. Mutualism
D. Predation

Answer: C. Mutualism
Explanation: Both fungus and plant roots benefit mutually.

Q30. Which vitamin is produced by gut bacteria?
A. Vitamin A
B. Vitamin C
C. Vitamin K
D. Vitamin D

Answer: C. Vitamin K
Explanation: Intestinal bacteria synthesize Vitamin K.

Section D: Biotechnology (10 MCQs)

Q31. Restriction enzymes cut DNA at:
A. Random sites
B. Specific sequences
C. RNA primers
D. Phosphate groups

Answer: B. Specific sequences
Explanation: Restriction enzymes recognize palindromic sequences.

Q32. PCR stands for:
A. Protein Chain Reaction
B. Polymerase Chain Reaction
C. Primary Cell Reaction
D. Phosphate Chain Reaction

Answer: B. Polymerase Chain Reaction
Explanation: PCR amplifies DNA segments in vitro.

Q33. The commonly used vector in genetic engineering is:
A. Virus
B. Plasmid
C. Ribosome
D. Chromosome

Answer: B. Plasmid
Explanation: Plasmids carry foreign DNA into host cells.

Q34. Which enzyme joins DNA fragments?
A. Ligase
B. Polymerase
C. Helicase
D. Primase

Answer: A. Ligase
Explanation: DNA ligase seals nicks by forming phosphodiester bonds.

Q35. Bt cotton is resistant to:
A. Fungi
B. Virus
C. Insects
D. Weeds

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

Q36. Insulin was first produced using:
A. Yeast
B. Virus
C. E. coli
D. Algae

Answer: C. E. coli
Explanation: Recombinant DNA technology used E. coli to produce human insulin.

Q37. Which is a selectable marker?
A. Antibiotic resistance gene
B. Promoter
C. Terminator
D. Origin of replication

Answer: A. Antibiotic resistance gene
Explanation: It helps identify transformed cells.

Q38. Gel electrophoresis separates DNA based on:
A. Shape
B. Charge
C. Size
D. Sequence

Answer: C. Size
Explanation: Smaller DNA fragments move faster through the gel.

Q39. Bioreactors are used for:
A. DNA extraction
B. Gene sequencing
C. Large-scale production
D. Cloning vectors

Answer: C. Large-scale production
Explanation: Bioreactors maintain optimal conditions for microbial growth.

Q40. RNA interference is used to:
A. Amplify genes
B. Silence genes
C. Express proteins
D. Cut DNA

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

Section E: Ecology and Environment (10 MCQs)

Q41. The pyramid of energy is always:
A. Inverted
B. Upright
C. Spindle-shaped
D. Irregular

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

Q42. The major cause of biodiversity loss is:
A. Pollution
B. Overpopulation
C. Habitat loss
D. Climate change

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

Q43. Primary producers are:
A. Herbivores
B. Carnivores
C. Decomposers
D. Autotrophs

Answer: D. Autotrophs
Explanation: They synthesize food using sunlight or chemicals.

Q44. Ozone depletion is mainly caused by:
A. CO₂
B. SO₂
C. CFCs
D. NO₂

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

Q45. The most abundant biogeochemical cycle is:
A. Carbon
B. Nitrogen
C. Phosphorus
D. Water

Answer: D. Water
Explanation: The hydrological cycle involves massive movement of water.

Q46. Which gas causes global warming?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Helium

Answer: C. Carbon dioxide
Explanation: CO₂ traps heat and contributes to the greenhouse effect.

Q47. Lichens are indicators of:
A. Water pollution
B. Soil fertility
C. Air pollution
D. Radiation

Answer: C. Air pollution
Explanation: Lichens are sensitive to SO₂ in air.

Q48. The 10% law was proposed by:
A. Darwin
B. Lindeman
C. Odum
D. Mendel

Answer: B. Lindeman
Explanation: Only about 10% of energy is transferred to the next trophic level.

Q49. Eutrophication occurs due to excess of:
A. Oxygen
B. Nutrients
C. Salts
D. Pesticides

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

Q50. Which is an example of in-situ conservation?
A. Zoo
B. Botanical garden
C. National park
D. Seed bank

Answer: C. National park
Explanation: In-situ conservation protects species in their natural habitat.

✅ These 50 NCERT-aligned MCQs comprehensively cover the CBSE Class 12 Biology syllabus and are ideal for board exam preparation.