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Class 12 Biology Online Practice, Chapter-wise
Each test below covers one Biology chapter from the Class 12 book. Our teachers built these to match the CBSE 2026-27 marking scheme closely. Click a chapter to start - there's no login, and you can try a test as many times as you want.
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Quick Practice - Class 12 Biology (NCERT Core) Select any chapter below to test your understanding with 5 high-yield multiple-choice questions, instant scoring, and step-by-step verified explanations. Q1.What is the ploidy level of the Primary Endosperm Nucleus (PEN) in typical angiosperms after double fertilization? Answer: (c) Triploid (3n). Triple fusion involves the fusion of one haploid male gamete (n) with the diploid central cell containing two polar nuclei (2n), forming a triploid (3n) primary endosperm nucleus.
Q2.The filiform apparatus is a characteristic cellular feature present in: Answer: (b) Synergids. The filiform apparatus consists of special finger-like cellular thickenings at the micropylar tip of the synergids that guide the entry of the pollen tube into the embryo sac.
Q3.What type of pollination takes place in cleistogamous flowers (e.g., in Viola, Oxalis, and Commelina)? Answer: (a) Invariable Autogamy (Self-pollination). Cleistogamous flowers never open at all. As anthers dehisce inside the closed bud, pollen grains directly land on the stigma, assuring seed-set without pollinators.
Q4.The functional megaspore in a developing angiosperm ovule develops into the mature female gametophyte (embryo sac) through: Answer: (d) 3 sequential free-nuclear mitotic divisions. The single functional megaspore nucleus undergoes three successive rounds of free-nuclear mitosis to form an 8-nucleate, 7-celled mature embryo sac.
Q5.The phenomenon of production of seeds without fertilization, mimicking sexual reproduction, is called: Answer: (b) Apomixis. Apomixis is a form of asexual reproduction seen in grasses and Asteraceae where seeds develop directly without syngamy or meiosis.
Q1.Which cells in the human testes are stimulated by Luteinizing Hormone (LH) to synthesize and secrete androgens (Testosterone)? Answer: (a) Leydig (Interstitial) Cells. Leydig cells located in the interstitial spaces between seminiferous tubules respond to LH pulses by producing testosterone. Sertoli cells support and nourish developing sperms.
Q2.Ovulation in human females occurs around the 14th day of the menstrual cycle in response to a rapid surge of: Answer: (c) Luteinizing Hormone (LH Surge). Maximum levels of LH (LH surge) during mid-cycle induce the rupture of the mature Graafian follicle and release of the secondary oocyte into the peritoneal cavity.
Q3.At what stage of embryonic development does implantation into the endometrium of the human uterus occur? Answer: (b) Blastocyst. The outer trophoblast layer of the blastocyst attaches to the uterine endometrium, and the inner cell mass differentiates into the embryo proper.
Q4.The primary physiological role of the hormone Progesterone during pregnancy is to: Answer: (d) Maintain the thickened secretory uterine endometrium for pregnancy support. Secreted by the corpus luteum and later by the placenta, progesterone prevents endometrial shedding and suppresses uterine wall contractions.
Q5.What is the structural role of the acrosome located at the anterior tip of the mammalian sperm head? Answer: (a) Contains hydrolytic enzymes that digest the zona pellucida of the ovum. The acrosome (derived from the Golgi complex) releases sperm lysins upon contact to penetrate the egg's protective coats during fertilization.
Q1.'Saheli', an oral contraceptive pill developed by the Central Drug Research Institute (CDRI) Lucknow, is chemically a: Answer: (c) Non-steroidal 'once-a-week' selective estrogen receptor modulator (Centchroman). Saheli is a non-steroidal oral pill taken once a week with very high contraceptive efficacy and minimal systemic side effects.
Q2.Which of the following Intrauterine Devices (IUDs) functions primarily by releasing copper ions into the uterus? Answer: (b) CuT, Cu7, and Multiload 375. Released Cu ions suppress sperm motility and reduce their fertilizing capacity while increasing phagocytosis of sperms in the uterus.
Q3.In the Assisted Reproductive Technology technique called ZIFT (Zygote Intra-Fallopian Transfer): Answer: (a) A zygote or early embryo up to 8 blastomeres is transferred into the fallopian tube. ZIFT transfers embryos at the ≤8-cell stage into the fallopian tube. If the embryo is >8 blastomeres, it is transferred to the uterus (IUT).
Q4.Statutory ban on Amniocentesis in India was enforced primarily to prevent: Answer: (d) Misuse for prenatal sex determination leading to female foeticide. Amniocentesis was developed to detect fetal genetic defects, but was banned under the PCPNDT Act to stop illegal sex-selective abortions.
Q5.Surgical sterilization in human males, involving cutting and tying of a small part of the vas deferens, is termed: Answer: (b) Vasectomy. Vasectomy is a terminal sterilization method that blocks sperm transport from the epididymis to the urethra without affecting semen volume or hormone production.
Q1.In garden pea plants (Pisum sativum), what is the phenotypic ratio obtained in the F2 generation of a classical Mendelian Dihybrid Cross? Answer: (a) 9 : 3 : 3 : 1. Crossing heterozygous round-yellow peas (RrYy × RrYy) gives 9 Round-Yellow, 3 Round-Green, 3 Wrinkled-Yellow, and 1 Wrinkled-Green plant in the F2 generation.
Q2.In snapdragon (Antirrhinum majus), crossing pure red (RR) with pure white (rr) flowers produces all pink (Rr) F1 flowers due to: Answer: (b) Incomplete Dominance. The red allele is not completely dominant over the white allele, resulting in an intermediate pink phenotype where both phenotypic and genotypic F2 ratios are 1 : 2 : 1.
Q3.A point mutation in the beta-globin chain gene that substitutes Glutamic acid with Valine at the 6th position causes: Answer: (c) Sickle-cell Anaemia. A single base substitution from GAG to GUG in the sixth codon replaces hydrophilic glutamic acid with hydrophobic valine, leading to sickle-shaped RBCs under low oxygen.
Q4.Down's syndrome in humans is caused by which numerical chromosomal aberration? Answer: (a) Trisomy of autosome chromosome 21 (2n + 1 = 47). First described by Langdon Down in 1866, Down's syndrome results from non-disjunction of chromosome 21 during gametogenesis.
Q5.What is the frequency of recombinant offspring if two genes are located very close to each other on the same chromosome (tight linkage)? Answer: (d) Very low, with parental types predominating. T.H. Morgan demonstrated in Drosophila that tightly linked genes rarely cross over, leading to high parental gene combinations and minimal non-parental recombinants.
Q1.In a double-stranded B-DNA molecule, if Adenine constitutes 30% of the total nitrogenous bases, what percentage is Cytosine? Answer: (b) 20%. By Chargaff's rules, %A = %T = 30%, totaling 60%. The remaining 40% is equally split between Guanine and Cytosine (%G = %C = 20%).
Q2.The unambiguous experiment using radioactive isotopes 32P and 35S that proved DNA is the genetic material was conducted by: Answer: (a) Alfred Hershey and Martha Chase (1952). By labeling bacteriophage T2 DNA with 32P and protein coats with 35S, they proved that only viral DNA enters the bacterial host to direct replication.
Q3.In the lac operon of E. coli, the structural gene z codes for which enzyme? Answer: (c) β-Galactosidase. Gene z codes for β-galactosidase (hydrolyzes lactose into glucose and galactose), gene y codes for permease, and gene a codes for transacetylase.
Q4.The process of removing non-coding introns and joining coding exons together in eukaryotic hnRNA is termed: Answer: (b) RNA Splicing. In eukaryotes, primary transcripts (hnRNA) contain non-functional introns that are excised by spliceosomes while functional exons are ligated to form mature mRNA.
Q5.Which of the following codons functions as the universal Initiator codon and codes for the amino acid Methionine? Answer: (a) AUG. AUG has dual functions: it acts as the primary start codon during translation initiation and codes for methionine. UAA, UAG, and UGA are stop codons.
Q1.The forelimbs of humans, cheetahs, whales, and bats share a similar skeletal anatomy despite performing different functions, illustrating: Answer: (b) Homologous organs (Divergent Evolution). Homology indicates common anatomical ancestry adapted to different environmental niches through divergent evolution.
Q2.In the Miller-Urey experiment simulating prebiotic Earth conditions, which mixture of gases was sparked with electric discharge? Answer: (d) CH4, H2, NH3, and water vapor at 800°C. Miller created electric discharge in a closed flask containing methane, ammonia, hydrogen, and boiling water, synthesizing simple amino acids (glycine, alanine).
Q3.According to the Hardy-Weinberg equilibrium (p2 + 2pq + q2 = 1), allele frequencies in a population remain constant provided there is: Answer: (a) Random mating and absence of evolutionary forces. Gene frequencies remain stable over generations in large, randomly mating populations with no genetic drift, mutation, or selection pressure.
Q4.Darwin's Finches on the Galapagos Islands with varied beak adaptations represent a classic textbook example of: Answer: (c) Adaptive Radiation. Adaptive radiation is the evolutionary process where an ancestral seed-eating stock diversifies into distinct ecological niches with specialized beaks (insectivorous, vegetarian).
Q5.Hugo de Vries proposed the Mutation Theory of Evolution working on the evening primrose (Oenothera lamarckiana), stating mutations are: Answer: (b) Random, discontinuous, and directionless (Saltation). Unlike Darwin's gradual minor variations, de Vries believed speciation is driven by single-step, large, sudden mutations called saltation.
Q1.The toxic crystalline substance released when malarial parasites rupture human erythrocytes, causing recurring fever and chills, is: Answer: (c) Haemozoin. The breakdown of red blood cell hemoglobin by multiplying Plasmodium merozoites produces toxic insoluble haemozoin granules, causing clinical malarial paroxysms.
Q2.Which primary immune cells are selectively infected and progressively destroyed by HIV, causing collapse of the adaptive immune system? Answer: (b) Helper T-lymphocytes (TH / CD4+ cells). HIV attacks CD4+ helper T-cells. As their count drops below critical thresholds, the patient develops vulnerability to opportunistic pathogens.
Q3.Colostrum, the yellowish fluid secreted by the mother during initial days of lactation, provides immediate passive immunity because it is rich in: Answer: (a) Secretory IgA Antibodies. IgA dimers in breast colostrum coat mucosal surfaces in the infant's gut, shielding against bacterial and viral invasion.
Q4.The standard clinical diagnostic serological test used to confirm Typhoid fever in patients is the: Answer: (d) Widal Test. The Widal test detects specific agglutinating antibodies against O and H antigens of Salmonella typhi in blood serum.
Q5.Malignant tumors spread and form secondary tumors at distant anatomical sites through blood and lymph via: Answer: (b) Metastasis. Metastasis is the hallmark characteristic of malignant cancers where sloughed tumor cells colonize distant tissues.
Q1.Which fungus is commercially cultivated for the industrial production of the immunosuppressive drug Cyclosporin A? Answer: (a) Trichoderma polysporum. Trichoderma polysporum produces Cyclosporin A, which suppresses organ transplant graft rejection by inhibiting T-cell activation.
Q2.Statins, bioactive molecules that competitively inhibit HMG-CoA reductase to lower blood cholesterol, are produced by the yeast: Answer: (c) Monascus purpureus. The red fermented yeast Monascus purpureus produces statins that block the rate-limiting enzyme in cholesterol synthesis.
Q3.What is the primary biological objective of the secondary (biological) treatment of municipal sewage water? Answer: (b) Reducing Biochemical Oxygen Demand (BOD) using aerobic microbial flocs. Aerobic microbes in aeration tanks digest organic matter into carbon dioxide and water, reducing the wastewater's BOD before discharge.
Q4.The large holes and porous texture in Swiss Cheese are caused by the release of carbon dioxide gas by: Answer: (d) Propionibacterium sharmanii. During fermentation, P. sharmanii produces large amounts of CO2 that form the characteristic round eyes (holes) in Swiss cheese.
Q5.Which of the following fungal-root symbiotic associations (Mycorrhiza) assists plants primarily by absorbing phosphorus from the soil? Answer: (a) Glomus. Fungi belonging to the genus Glomus form endomycorrhizae, absorbing soil phosphorus and conferring resistance to root-borne pathogens and salinity.
Q1.Restriction endonucleases cleave phosphodiester backbones of double-stranded DNA by recognizing specific: Answer: (c) Palindromic nucleotide sequences. Restriction enzymes bind and cleave double-stranded DNA at palindromic sites that read identically in the 5' → 3' direction on both strands.
Q2.Why is the thermostable enzyme Taq Polymerase used during the Extension step of the Polymerase Chain Reaction (PCR)? Answer: (b) It resists denaturation during repeated high-temperature cycles. Isolated from the thermophilic bacterium Thermus aquaticus, Taq polymerase stays active through automated high-temperature PCR cycles.
Q3.In agarose gel electrophoresis, DNA fragments separate according to their size and migrate toward the anode because DNA is: Answer: (a) Negatively charged due to phosphate groups, with smaller fragments traveling farther. The agarose gel acts as a sieve. Negatively charged DNA fragments move toward the positive electrode (anode) at rates inversely proportional to their base-pair length.
Q4.In plasmid pBR322, insertional inactivation of the β-galactosidase (lacZ) gene by foreign DNA produces: Answer: (d) White (colorless) recombinant bacterial colonies. Inserting foreign DNA disrupts the lacZ gene, preventing functional β-galactosidase synthesis. Recombinant colonies remain white in the presence of chromogenic substrate X-gal.
Q5.What method of direct gene transfer introduces foreign DNA into plant cells by bombarding them with micro-particles of gold or tungsten? Answer: (b) Biolistics / Gene Gun Method. Biolistics accelerates DNA-coated microscopic gold or tungsten beads at high velocity to penetrate tough plant cell walls.
Q1.Why do the crystalline Cry proteins produced by Bacillus thuringiensis not kill the bacterium itself? Answer: (d) The toxin exists as an inactive protoxin and requires the alkaline pH of the insect midgut for activation. Ingested protoxin crystals dissolve in the alkaline insect midgut, where proteases cleave them into active endotoxins that create lethal membrane pores.
Q2.RNA interference (RNAi) protects tobacco plants from the root-knot nematode Meloidogyne incognita by: Answer: (a) Post-transcriptional gene silencing of specific nematode mRNA using complementary dsRNA. Transgenic plants produce sense and anti-sense RNA forming double-stranded RNA (dsRNA), which triggers RISC-mediated cleavage of target nematode mRNA.
Q3.How did Eli Lilly & Company synthesize genetically engineered human insulin (Humulin) in 1983? Answer: (c) Produced insulin chains A and B separately in E. coli and bonded them with disulfide bridges. They engineered two separate DNA sequences for chains A and B, expressed them in E. coli, and joined the purified chains with synthetic disulfide bonds.
Q4.The first clinical gene therapy was administered in 1990 to a 4-year-old girl suffering from Severe Combined Immunodeficiency (SCID) caused by deficiency of: Answer: (b) Adenosine Deaminase (ADA). Functional ADA cDNA was delivered into cultured patient lymphocytes using a disarmed retroviral vector and infused back to restore immune function.
Q5.Transgenic 'Golden Rice' was genetically engineered with β-carotene biosynthesis genes to combat human deficiency of: Answer: (a) Vitamin A. Golden Rice expresses daffodil and bacterial enzymes that synthesize provitamin A (β-carotene) in the edible grain endosperm to prevent night blindness.
Q1.According to Allen's Rule, mammals adapted to colder arctic climates typically possess: Answer: (b) Shorter ears and shorter limbs to minimize heat loss. Allen's rule states that endothermic animals from colder climates have shorter extremities to reduce exposed surface area and conserve body heat.
Q2.The population interaction between an epiphytic orchid growing on a mango branch, where the orchid benefits and the mango tree is unaffected, is: Answer: (c) Commensalism (+ / 0). In commensalism, one species derives shelter or support (+) while the host organism experiences neither harm nor benefit (0).
Q3.In the Verhulst-Pearl Logistic Growth equation dN/dt = rN [(K - N) / K], the variable 'K' represents: Answer: (a) Environmental Carrying Capacity. 'K' is the maximum population size an ecosystem can sustain indefinitely given limited food, shelter, and space.
Q4.Gause's Principle of Competitive Exclusion states that: Answer: (d) Two species competing for the exact same limiting resources cannot coexist. Gause demonstrated that identical niche requirements lead to the competitive exclusion of the less efficient competitor.
Q5.A physiological adaptation where organisms suspend development to survive unfavorable seasonal conditions, as seen in zooplankton, is: Answer: (b) Diapause. Diapause is a state of suspended metabolic development in many zooplankton and insects to survive unfavorable environmental stress.
Q1.Why is the ecological Pyramid of Energy always upright in all natural ecosystems without exception? Answer: (c) Energy transfer between trophic levels follows Lindeman's 10% law. Energy flow is strictly unidirectional and obeys thermodynamics; energy decreases progressively at each higher trophic tier.
Q2.The Pyramid of Biomass in an open ocean / aquatic ecosystem is typically: Answer: (a) Inverted. Phytoplankton have a short lifespan and high turnover rate, meaning their standing biomass at any single moment is less than that of long-lived zooplankton and fishes.
Q3.What is the rate of biomass production available for consumption by heterotrophs (NPP = GPP - R) called? Answer: (b) Net Primary Productivity (NPP). NPP is the total solar energy fixed into organic biomass (GPP) minus the respiratory losses (R) incurred by producers.
Q4.In ecological succession on bare rock (Xerarch succession), which organisms act as the pioneering species? Answer: (d) Crustose lichens. Crustose lichens secrete organic acids that weather hard rock into mineral soil, paving the way for bryophytes and grasses.
Q5.The breakdown of detritus into smaller particulate fragments by earthworms and detritivores is termed: Answer: (a) Fragmentation. Decomposition follows five steps: Fragmentation (by detritivores), Leaching, Catabolism (by fungal/bacterial enzymes), Humification, and Mineralization.
Q1.Which of the following is classified as an Ex-Situ (Off-Site) biodiversity conservation strategy? Answer: (b) Zoological Parks, Botanical Gardens, and Cryopreservation. Ex-situ conservation removes endangered animals and plants from threatened natural habitats into specialized human-managed facilities.
Q2.According to the Species-Area relationship established by Alexander von Humboldt, on a logarithmic scale the curve is a straight line described by: Answer: (c) log S = log C + Z log A. Plotted on logarithmic coordinates, species richness (S) versus area (A) yields a linear slope where Z represents the regression coefficient.
Q3.Among the 'Evil Quartet' drivers of human-induced biodiversity loss, which factor is considered the single most significant cause? Answer: (a) Habitat Loss and Fragmentation. Clearing natural forest covers for agriculture and cattle pasture represents the leading direct cause of species extinctions globally.
Q4.In Paul Ehrlich's 'Rivet Popper Hypothesis', what component of the ecosystem is compared to the rivets of an airplane? Answer: (d) Individual biological species within the ecosystem. Popping rivets represents species extinctions. Losing a few interior rivets causes minor impairment, but losing key wing rivets (keystone species) threatens catastrophic system failure.
Q5.The international landmark environmental treaty signed at the 1992 Earth Summit in Rio de Janeiro to promote biodiversity conservation is: Answer: (b) Convention on Biological Diversity (CBD). CBD committed signatory nations to conserve biological diversity, use biological components sustainably, and equitably share benefits from genetic resources.
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