Biological ClassificationNEET MCQs with solutions

Not quite — the answer is C.

Age of an organism has no taxonomic significance and is not used as a classification criterion. Cell organization, evolutionary relationships, and mode of nutrition are all explicitly recognized criteria in modern systematics.

Not quite — the answer is D.

Internal cell organization is more fundamental than superficial morphology. Two organisms may convergently evolve similar body forms (analogous structures) while being phylogenetically distant; cell structure reflects true evolutionary position.

Not quite — the answer is A.

Cyanobacteria are photosynthetic but prokaryotic. Cell structure (absence of true nucleus) overrides nutritional mode in determining kingdom placement — this organism belongs to Monera, not Plantae, despite being photosynthetic.

Not quite — the answer is D.

Monera are prokaryotic and completely lack membrane-bound organelles, including mitochondria. Options A, B, and C are all defining features of Monera. Mitochondria are eukaryotic organelles present in Protista, Fungi, Plantae, and Animalia.

Not quite — the answer is B.

The defining feature of Monera is prokaryotic cell organization — absence of true nucleus and membrane-bound organelles. Not all Monera are extremophiles; many are heterotrophic; and some reproduce by means other than simple binary fission (e.g., conjugation).

Not quite — the answer is A.

Photosynthetic protists (e.g., diatoms, green algae) are eukaryotic and possess chlorophyll — identical to plants in those features. The distinguishing criterion is tissue differentiation and embryo formation, which are hallmarks of Plantae absent in Protista.

Not quite — the answer is D.

Prokaryotes definitively lack a membrane-bound nucleus — their DNA is in the nucleoid, an unenclosed cytoplasmic region. Options A (70S ribosomes), B (nucleoid), and C (plasmids) are all genuine prokaryotic features that serve as common distractors.

Not quite — the answer is B.

Nitrification is a two-step aerobic chemosynthetic process: Nitrosomonas oxidizes NH₃ → NO₂⁻; Nitrobacter oxidizes NO₂⁻ → NO₃⁻. Both derive energy from these inorganic oxidations. Nitrogen fixation (N₂ → NH₃) is performed by different bacteria (Rhizobium, Azotobacter); denitrification is performed by Pseudomonas.

Not quite — the answer is B.

Nitrogenase enzyme is irreversibly inactivated by oxygen. Heterocysts lack Photosystem II (which evolves O₂) and have thick walls with extra glycolipid layers — creating the anaerobic microenvironment nitrogenase requires. Vegetative cells perform photosynthesis; heterocysts fix nitrogen.

Not quite — the answer is B.

NCERT classifies protozoans into: amoeboid (pseudopodia), flagellated (flagella), ciliated (cilia), and sporozoans (no locomotor organelle in adult stage). Locomotion is the primary grouping criterion — not reproduction or pigmentation.

Not quite — the answer is A.

E. histolytica uses pseudopodia to invade intestinal epithelium and produces proteases that lyse host cells — causing flask-shaped ulcers, bloody mucoid stools (dysentery), and potentially liver abscess if it enters the portal circulation. It is transmitted via faecal-oral route through contaminated food or water.

Not quite — the answer is C.

During conjugation, two compatible Paramecium cells align and form a cytoplasmic bridge. Micronuclei undergo meiosis; haploid micronuclei are exchanged reciprocally. After separation, each cell reconstitutes its macronucleus from the new micronucleus — achieving genetic recombination without increase in cell number.

Not quite — the answer is C.

Ascomycetes form ascospores inside sac-like structures called asci — this naming is directly from NCERT. "Water moulds" (Oomycetes) are no longer classified as fungi; this option tests whether students confuse older classifications.

Not quite — the answer is A.

Sexual reproduction in fungi follows plasmogamy (cytoplasm fusion), then karyogamy (nuclear fusion), then meiosis to restore haploid state. Reversing karyogamy and meiosis is the most common student error — Option D is the classic trap.

Not quite — the answer is A.

In Phycomycetes, zygospores form by the fusion of two gametangia (gametangial copulation), producing a thick-walled, resistant resting spore. Option B confuses basidiospores (which are already post-meiotic products) with zygospore parents; Option C incorrectly assigns asci to Phycomycetes.

Not quite — the answer is D.

Virology is the branch of microbiology focused on viruses — their structure, classification, replication, and disease causation. While this is an EASY recall question, it anchors the foundational vocabulary expected in NEET.

Not quite — the answer is C.

BSE is caused by prions — abnormally folded PrP (prion protein) that induces misfolding of normal PrP in neural tissue, leading to spongiform neurodegeneration. Option A (viroid) is the most common wrong answer — students confuse prions and viroids as both being "sub-viral agents."

Not quite — the answer is B.

NCERT describes: Ivanowsky (1892) showed tobacco mosaic disease was caused by a filterable agent smaller than bacteria; Beijerinck (1898) demonstrated the agent was a "contagium vivum fluidum" (living fluid) that could reproduce; Stanley (1935) crystallised TMV, proving its chemical nature. Diener (viroid discoverer) is from a later and separate context.

Not quite — the answer is A.

Potato spindle tuber disease is the classic NCERT example of a viroid-caused plant disease. Mad cow disease is caused by a prion; polio by a virus; TMD by TMV (a virus).

Not quite — the answer is B.

The defining structural simplicity of viroids is the complete absence of a protein coat — all viruses, at minimum, have a capsid surrounding their nucleic acid. Option C is a trap: size and gene count are consequences, not the primary structural distinction.

Not quite — the answer is C.

Viroids are naked infectious RNA — no protein, no DNA, no envelope. Option D precisely describes prions — the ELITE trap for students who mix up the two anomalous infectious agents.

Not quite — the answer is A.

BSE (mad cow disease) is the NCERT-cited prion disease. Potato spindle tuber disease = viroid; Polio and Influenza = viruses.

Not quite — the answer is D.

Prion diseases produce characteristic sponge-like vacuolation and holes in brain tissue, leading to irreversible neurodegeneration. Options A and B wrongly imply bacterial or viral involvement.

Not quite — the answer is A.

Prions propagate by forcing normal PrPᶜ proteins to adopt the abnormal PrPˢᶜ conformation — a self-propagating chain reaction requiring no nucleic acid. Option D is the top trap: aggregation occurs, but translation is not involved since prions encode nothing.