NCERT-Based MCQs for CBSE Class 12 Biology – Exam Ready

(Strictly as per NCERT | Board-Oriented | With Detailed Explanations)

Section A: Reproduction (10 MCQs)

Q1. The hormone responsible for the growth of ovarian follicles in human females is:
A. LH
B. FSH
C. Progesterone
D. Estrogen

Answer: B. FSH
Explanation: Follicle Stimulating Hormone (FSH) stimulates the growth and maturation of ovarian follicles during the follicular phase.

Q2. Which part of the ovule develops into seed coat after fertilization?
A. Nucellus
B. Integuments
C. Embryo sac
D. Endosperm

Answer: B. Integuments
Explanation: The integuments harden to form the protective seed coat.

Q3. The gestation period in humans is approximately:
A. 180 days
B. 240 days
C. 270 days
D. 300 days

Answer: C. 270 days
Explanation: Human pregnancy lasts about 9 months or 270 days.

Q4. Which structure nourishes the developing embryo in angiosperms?
A. Cotyledon
B. Perisperm
C. Endosperm
D. Plumule

Answer: C. Endosperm
Explanation: Endosperm stores food and provides nutrition to the developing embryo.

Q5. Which hormone is known as the “birth hormone”?
A. Estrogen
B. Progesterone
C. Prolactin
D. Oxytocin

Answer: D. Oxytocin
Explanation: Oxytocin induces uterine contractions during childbirth.

Q6. Vegetative propagation is an example of:
A. Sexual reproduction
B. Asexual reproduction
C. Apomixis
D. Amphimixis

Answer: B. Asexual reproduction
Explanation: New plants are produced without gamete fusion.

Q7. The functional megaspore in angiosperms is:
A. Uppermost
B. Lowermost (chalazal end)
C. Central
D. Micropylar

Answer: B. Lowermost (chalazal end)
Explanation: Only one megaspore survives and develops into embryo sac.

Q8. Which contraceptive method also protects against STDs?
A. IUD
B. Oral pills
C. Condom
D. Sterilization

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

Q9. Menstrual cycle is regulated by hormones from:
A. Ovary only
B. Pituitary only
C. Hypothalamus and pituitary
D. Ovary, pituitary and hypothalamus

Answer: D. Ovary, pituitary and hypothalamus
Explanation: Coordinated hormonal control regulates the menstrual cycle.

Q10. After fertilization, ovary converts into:
A. Fruit
B. Seed
C. Endosperm
D. Pericarp

Answer: A. Fruit
Explanation: The ovary wall develops into fruit, while ovules form seeds.

Section B: Genetics and Evolution (10 MCQs)

Q11. The inheritance pattern showing both alleles expressed equally is:
A. Incomplete dominance
B. Codominance
C. Pleiotropy
D. Polygenic inheritance

Answer: B. Codominance
Explanation: In codominance, both alleles express fully, e.g., ABO blood group.

Q12. The number of linkage groups in humans is:
A. 22
B. 23
C. 44
D. 46

Answer: B. 23
Explanation: Each chromosome represents one linkage group.

Q13. Which nitrogenous base is absent in RNA?
A. Adenine
B. Guanine
C. Thymine
D. Cytosine

Answer: C. Thymine
Explanation: RNA contains uracil instead of thymine.

Q14. The enzyme that unwinds DNA during replication is:
A. Ligase
B. Helicase
C. Primase
D. Polymerase

Answer: B. Helicase
Explanation: Helicase breaks hydrogen bonds between DNA strands.

Q15. Which disorder is caused by trisomy of chromosome 21?
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Edwards syndrome

Answer: C. Down syndrome
Explanation: Presence of an extra chromosome 21 causes Down syndrome.

Q16. Evolutionary fitness refers to:
A. Physical strength
B. Long life span
C. Reproductive success
D. Body size

Answer: C. Reproductive success
Explanation: Fitness is measured by the ability to pass genes to next generation.

Q17. The start codon for protein synthesis is:
A. UAA
B. UAG
C. AUG
D. UGA

Answer: C. AUG
Explanation: AUG codes for methionine and initiates translation.

Q18. Speciation occurs due to:
A. Mutation only
B. Reproductive isolation
C. Migration
D. Random mating

Answer: B. Reproductive isolation
Explanation: Isolation prevents gene flow, leading to speciation.

Q19. Which RNA carries genetic information from DNA to ribosome?
A. tRNA
B. rRNA
C. mRNA
D. snRNA

Answer: C. mRNA
Explanation: mRNA acts as a template for protein synthesis.

Q20. Homologous organs indicate:
A. Convergent evolution
B. Adaptive radiation
C. Divergent evolution
D. Parallel evolution

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

Section C: Biology in Human Welfare (10 MCQs)

Q21. Which microorganism fixes atmospheric nitrogen in legume roots?
A. Azotobacter
B. Nostoc
C. Rhizobium
D. Anabaena

Answer: C. Rhizobium
Explanation: Rhizobium forms symbiotic nodules in legume roots.

Q22. Which disease is caused by a virus?
A. Typhoid
B. Malaria
C. AIDS
D. Cholera

Answer: C. AIDS
Explanation: AIDS is caused by Human Immunodeficiency Virus (HIV).

Q23. The most commonly used biofertilizer is:
A. Algae
B. Fungi
C. Bacteria
D. Protozoa

Answer: C. Bacteria
Explanation: Nitrogen-fixing bacteria enrich soil fertility.

Q24. Which antibiotic is obtained from fungus?
A. Streptomycin
B. Tetracycline
C. Penicillin
D. Erythromycin

Answer: C. Penicillin
Explanation: Penicillin is produced by Penicillium species.

Q25. Which vaccine is a live attenuated vaccine?
A. IPV
B. OPV
C. Tetanus
D. Rabies

Answer: B. OPV
Explanation: Oral Polio Vaccine contains weakened live virus.

Q26. Biogas is produced by:
A. Aerobic bacteria
B. Anaerobic bacteria
C. Algae
D. Fungi

Answer: B. Anaerobic bacteria
Explanation: Methanogens work in anaerobic conditions.

Q27. Which disease spreads through contaminated water?
A. Malaria
B. Dengue
C. Cholera
D. Tuberculosis

Answer: C. Cholera
Explanation: Cholera is a water-borne bacterial disease.

Q28. Which organism is used as SCP?
A. Cow
B. Fish
C. Yeast
D. Frog

Answer: C. Yeast
Explanation: Yeast provides protein-rich biomass.

Q29. Antibiotic resistance develops due to:
A. Mutation
B. Overuse of antibiotics
C. Natural selection
D. All of the above

Answer: D. All of the above
Explanation: Resistance arises due to genetic changes and selection pressure.

Q30. Which is a biocontrol agent?
A. Pesticide
B. Ladybird beetle
C. Fertilizer
D. Herbicide

Answer: B. Ladybird beetle
Explanation: It preys on aphids and controls pests naturally.

Section D: Biotechnology (10 MCQs)

Q31. Restriction enzymes are also called:
A. Molecular scissors
B. Molecular glue
C. Molecular carriers
D. Molecular markers

Answer: A. Molecular scissors
Explanation: They cut DNA at specific sequences.

Q32. PCR requires which enzyme?
A. DNA ligase
B. Taq polymerase
C. RNA polymerase
D. Restriction enzyme

Answer: B. Taq polymerase
Explanation: It is heat stable and functions at high temperatures.

Q33. Which bacterium is used to produce human insulin?
A. Salmonella
B. Bacillus
C. E. coli
D. Lactobacillus

Answer: C. E. coli
Explanation: Recombinant DNA technology uses E. coli.

Q34. The plasmid transfers foreign DNA into:
A. Virus
B. Host cell
C. Ribosome
D. Nucleus

Answer: B. Host cell
Explanation: Plasmids act as cloning vectors.

Q35. Which is NOT a component of PCR?
A. Primers
B. DNA template
C. Ligase
D. dNTPs

Answer: C. Ligase
Explanation: DNA ligase is not required in PCR.

Q36. ELISA is based on:
A. DNA–DNA interaction
B. Antigen–antibody reaction
C. RNA synthesis
D. Enzyme inhibition

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

Q37. Which crop is genetically modified for pest resistance?
A. Wheat
B. Rice
C. Bt cotton
D. Barley

Answer: C. Bt cotton
Explanation: Contains Bt toxin gene.

Q38. Gene silencing technique is known as:
A. Cloning
B. PCR
C. RNA interference
D. Sequencing

Answer: C. RNA interference
Explanation: Prevents expression of target genes.

Q39. A bioreactor helps in:
A. DNA cutting
B. Cell lysis
C. Large-scale production
D. Gene transfer

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

Q40. Which marker gene is commonly used in plants?
A. lacZ
B. ampR
C. nptII
D. tetR

Answer: C. nptII
Explanation: Provides kanamycin resistance.

Section E: Ecology and Environment (10 MCQs)

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

Answer: D. Sun
Explanation: Solar energy drives all ecosystems.

Q42. Which trophic level has maximum energy?
A. Producers
B. Primary consumers
C. Secondary consumers
D. Tertiary consumers

Answer: A. Producers
Explanation: Energy decreases at higher trophic levels.

Q43. Which cycle does not have gaseous phase?
A. Nitrogen
B. Carbon
C. Water
D. Phosphorus

Answer: D. Phosphorus
Explanation: Phosphorus cycle lacks a gaseous phase.

Q44. Acid rain is caused due to:
A. CO₂
B. SO₂ and NO₂
C. Methane
D. Ozone

Answer: B. SO₂ and NO₂
Explanation: These gases form acids in atmosphere.

Q45. Which ecosystem has highest productivity?
A. Desert
B. Grassland
C. Tropical rainforest
D. Tundra

Answer: C. Tropical rainforest
Explanation: Favorable climate supports high productivity.

Q46. Ozone layer protects us from:
A. Infrared rays
B. Gamma rays
C. Ultraviolet rays
D. X-rays

Answer: C. Ultraviolet rays
Explanation: Ozone absorbs harmful UV radiation.

Q47. Biodiversity hotspot means:
A. High rainfall area
B. High population density
C. High endemic species
D. Industrial area

Answer: C. High endemic species
Explanation: Hotspots have rich and threatened biodiversity.

Q48. Which is an example of keystone species?
A. Grass
B. Tiger
C. Deer
D. Frog

Answer: B. Tiger
Explanation: Removal of tigers disrupts ecosystem balance.

Q49. Ex-situ conservation includes:
A. National parks
B. Wildlife sanctuaries
C. Zoological parks
D. Biosphere reserves

Answer: C. Zoological parks
Explanation: Conservation outside natural habitat.

Q50. The concept of ecological succession was proposed by:
A. Odum
B. Clements
C. Tansley
D. Darwin

Answer: B. Clements
Explanation: He explained orderly changes in community structure.

✅ This NCERT-based, exam-ready MCQ set ensures full syllabus coverage and is ideal for scoring high in CBSE Class 12 Biology board exams.