Class 12 Biology Last 5 Years MCQs – Free Practice
Class 12 Biology Last 5 Years MCQs - Online Practice — Practice Questions
1. Foetal ejection reflex in human female triggers the release of which hormone?
- (A) Oxytocin from foetal pituitary gland
- (B) hCG from placenta
- (C) Progesterone from corpus luteum
- (D) Oxytocin from maternal pituitary gland
Answer: (D) Oxytocin from maternal pituitary gland
Signals from the fully developed foetus and the placenta induce mild uterine contractions (foetal ejection reflex), which stimulates release of oxytocin from the mother's pituitary, further intensifying contractions in a positive feedback loop.
2. Which of the following is not a functional unit of an ecosystem?
- (A) Energy flow
- (B) Decomposition
- (C) Stratification
- (D) Productivity
Answer: (C) Stratification
Productivity, decomposition, energy flow, and nutrient cycling are the four basic functional components of an ecosystem. Stratification refers to the vertical layering of organisms (e.g. canopy, understorey) and is a structural feature, not a functional process.
3. Match Column I with Column II: a.Primers, b.Insertional inactivation, c.Bioreactor, d.Downstream processing / i.beta-galactosidase, ii.To separate and purify products, iii.Chemically synthesized oligonucleotides, iv.Large scale production of specific product of activity of microbes
- (A) a-iii, b-i, c-iv, d-ii
- (B) a-iii, b-i, c-ii, d-iv
- (C) a-i, b-iii, c-iv, d-ii
- (D) a-i, b-iv, c-ii, d-iii
Answer: (A) a-iii, b-i, c-iv, d-ii
Primers are short chemically synthesized oligonucleotides (iii); insertional inactivation is detected via loss of beta-galactosidase activity (i); a bioreactor allows large-scale microbial product formation (iv); downstream processing separates and purifies the final product (ii).
4. Golden rice is a promising transgenic crop. When released for cultivation, it will help in:
- (A) Producing petrol-like fuel
- (B) Reduction of Vitamin A deficiency in humans
- (C) Pest resistance
- (D) Herbicide tolerance
Answer: (B) Reduction of Vitamin A deficiency in humans
Golden rice is genetically engineered to biosynthesize beta-carotene (a Vitamin A precursor) in the edible part of the grain, aimed at addressing Vitamin A deficiency in populations dependent on rice as a staple.
5. Appearance of antibiotic-resistant bacteria is an example of evolution due to:
- (A) Adaptive radiation
- (B) Divergent evolution
- (C) Artificial selection
- (D) Anthropogenic action
Answer: (D) Anthropogenic action
Antibiotic resistance arises and spreads because of selection pressure created by human use (and overuse) of antibiotics, making it a human-driven (anthropogenic) evolutionary change, distinct from natural adaptive radiation or divergence.
6. Identify the statements that correctly describe Darwin's Theory of Evolution: (i) Overproduction of organisms leads to competition. (ii) Variation is inherited and causes evolution. (iii) Acquired characters are inherited. (iv) Survival depends on favourable traits. (v) New species arise due to accumulation of favourable variations.
- (A) (i), (ii), (iv) and (v) are correct
- (B) (ii), (iii) and (iv) are correct
- (C) All are correct
- (D) Only (i) and (iv) are correct
Answer: (A) (i), (ii), (iv) and (v) are correct
Darwin's natural selection theory includes overproduction/competition, heritable variation, survival of the fittest (favourable traits), and gradual accumulation of variations leading to new species. Statement (iii), inheritance of acquired characters, is Lamarckian, not Darwinian, so it is excluded.
7. Which of the following is not a symptom of Ascariasis?
- (A) Intestinal blockage
- (B) Muscular pain and fever
- (C) Anaemia
- (D) Skin ulcers
Answer: (D) Skin ulcers
Ascariasis (roundworm infection) commonly causes internal bleeding, muscular pain, fever, intestinal blockage, and anaemia due to nutrient loss. Skin ulcers are not a characteristic symptom of this infection.
8. Every trophic level has a certain mass of living material at a particular time. What is it called?
- (A) Standing crop
- (B) Primary productivity
- (C) Standing state
- (D) Ecological efficiency
Answer: (A) Standing crop
The standing crop refers to the biomass (or number of individuals) present at a given trophic level at a specific point in time, typically measured as mass of living organisms per unit area.
9. The smallest part of DNA molecule that can be changed by point mutation is:
- (A) Oligonucleotide
- (B) Codon
- (C) Gene
- (D) Nucleotide
Answer: (D) Nucleotide
A point mutation is a change at a single base-pair (nucleotide) position in the DNA sequence — it is the smallest unit that can be altered in this type of mutation.
10. Statements regarding drugs and alcohol: (i) Adolescents are more vulnerable to peer pressure. (ii) Drug addiction leads to increased tolerance level of receptors in our body. (iii) Alcohol affects the central nervous system. (iv) Excessive use of drugs helps to increase energy. (v) Anabolic steroids decrease aggressiveness.
- (A) (i), (iv) and (v) are correct
- (B) (i), (ii) and (iii) are correct
- (C) Only (i) and (v) are correct
- (D) Only (iii) is correct
Answer: (B) (i), (ii) and (iii) are correct
Adolescent vulnerability to peer pressure, increased receptor tolerance with addiction, and alcohol's depressant effect on the CNS are all correct, standard facts. Excessive drug use does not increase energy, and anabolic steroids are associated with increased (not decreased) aggressiveness, so (iv) and (v) are incorrect.
11. Select the correct option for the pair of plants pollinated by water:
- (A) Vallisneria and Hydrilla
- (B) Zostera and Water lily
- (C) Water lily and Parthenium
- (D) Water hyacinth and Water lily
Answer: (A) Vallisneria and Hydrilla
Vallisneria and Hydrilla are classic examples of hydrophilous (water-pollinated) plants. Water lily and water hyacinth, despite growing in water, are actually pollinated by insects, not by water itself.
12. Assertion (A): Activated sludge contains large population of bacteria. Reason (R): These bacteria help in anaerobic digestion of human waste in biogas plant.
- (A) Both A and R are true and R is the correct explanation of A
- (B) Both A and R are true but R is NOT the correct explanation of A
- (C) A is true but R is false
- (D) A is false but R is true
Answer: (C) A is true but R is false
Activated sludge does contain a large bacterial population (A is true), but this refers to the aerobic secondary sewage treatment process, not anaerobic digestion in a biogas plant — the anaerobic digestion described in R happens in a separate step/facility, so R as stated is false.
13. Assertion (A): Ecosystems require a constant supply of energy to synthesize the molecules they require. Reason (R): This is to counteract the universal tendency towards increasing disorderliness as per Second Law of Thermodynamics.
- (A) Both A and R are true and R is the correct explanation of A
- (B) Both A and R are true but R is NOT the correct explanation of A
- (C) A is true but R is false
- (D) A is false but R is true
Answer: (A) Both A and R are true and R is the correct explanation of A
Living systems continuously need energy input to build and maintain ordered biomolecules against the natural tendency toward disorder (entropy increase), as described by the Second Law of Thermodynamics — R correctly explains A.
14. Assertion (A): DNA cannot pass through cell membrane of a bacterial cell. Reason (R): DNA is a hydrophilic molecule.
- (A) Both A and R are true and R is the correct explanation of A
- (B) Both A and R are true but R is NOT the correct explanation of A
- (C) A is true but R is false
- (D) A is false but R is true
Answer: (D) A is false but R is true
DNA CAN be made to pass through a bacterial cell membrane under specific treatments (e.g. CaCl2 and heat shock in transformation), so A is false. DNA being a hydrophilic (polar) molecule is a true statement on its own, which is precisely why it cannot cross the membrane without such special treatment.
15. Assertion (A): Repetitive sequences are stretches of DNA sequences thought to have no direct coding functions. Reason (R): They shed light on chromosome structure, dynamics and evolution.
- (A) Both A and R are true and R is the correct explanation of A
- (B) Both A and R are true but R is NOT the correct explanation of A
- (C) A is true but R is false
- (D) A is false but R is true
Answer: (A) Both A and R are true and R is the correct explanation of A
Repetitive DNA sequences indeed lack direct protein-coding function, and studying them (e.g. via satellite DNA analysis) provides insight into chromosome structure, organization, and evolutionary history — both statements are true and connected.