Biological Classification MCQs for NEET

Question 1

Whittaker's five-kingdom classification is based primarily on which set of criteria?

Accepted Answer

Cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships — R. H. Whittaker (1969) proposed the five-kingdom system — Monera, Protista, Fungi, Plantae, Animalia — using cell structure (prokaryotic vs eukaryotic), body organisation (unicellular vs multicellular), mode of nutrition (autotrophic, heterotrophic — absorptive vs ingestive), reproduction, and phylogenetic relationships as the main criteria.

Question 2

Which of the following is NOT a characteristic of Archaebacteria?

Accepted Answer

They possess peptidoglycan in their cell walls — Archaebacteria lack peptidoglycan (murein) in their cell walls — a key difference from eubacteria. Their walls contain pseudopeptidoglycan or protein layers, and their membranes have branched-chain lipids that resist extreme temperature/pH. Methanogens, halophiles, and thermoacidophiles are the three main groups.

Question 3

Mycoplasma differ from all other prokaryotes because they:

Accepted Answer

Completely lack a cell wall — Mycoplasma are the smallest living cells known and are the only prokaryotes that completely lack a cell wall. This makes them pleomorphic and resistant to cell-wall targeting antibiotics like penicillin. They can survive without oxygen (many are anaerobic) and cause diseases in animals and plants.

Question 4

The 'red tides' in the sea are caused by rapid multiplication of:

Accepted Answer

Dinoflagellates such as Gonyaulax — Red tides are caused by red dinoflagellates (e.g., Gonyaulax) that multiply so rapidly the sea appears red. Toxins released by these dinoflagellates can kill fish and other marine animals. Dinoflagellates are photosynthetic Protists with two flagella — one longitudinal and one transverse.

Question 5

Diatomaceous earth is formed from the accumulated:

Accepted Answer

Silica-rich cell walls (frustules) of diatoms — Diatoms have indestructible cell walls made of two overlapping shells (frustules) that fit together like a soap-box, embedded with silica. Over billions of years, their accumulated cell walls formed 'diatomaceous earth', which is used in polishing, filtration of oils and syrups.

Question 6

Which of the following pairs is correctly matched with respect to fungi?

Accepted Answer

Ascomycetes — sac fungi, sexual spores are ascospores produced in asci — Ascomycetes (sac fungi) — e.g., Aspergillus, Claviceps, Neurospora — produce sexual spores called ascospores endogenously in sac-like asci. Phycomycetes have coenocytic hyphae and produce zoospores/aplanospores. Basidiomycetes produce basidiospores exogenously on basidia. Deuteromycetes ('fungi imperfecti') lack a known sexual stage.

Question 7

Viroids differ from viruses in that viroids:

Accepted Answer

Consist of free RNA without a protein coat, of lower molecular weight than viral RNA — Viroids were discovered by T. O. Diener (1971) as the causal agent of potato spindle tuber disease. They consist of free, low-molecular-weight RNA without a protein coat — smaller than viruses. Viruses always have a nucleic acid (DNA or RNA) enclosed in a protein capsid.

Question 8

Lichens represent a symbiotic association between:

Accepted Answer

An alga (phycobiont) and a fungus (mycobiont) — Lichens are symbiotic (mutualistic) associations between an alga (phycobiont — usually a green alga or cyanobacterium) that prepares food by photosynthesis, and a fungus (mycobiont — usually an ascomycete) that provides shelter and absorbs mineral nutrients and water. Lichens are excellent pollution indicators — they don't grow in polluted areas.

Question 9

Which of the following statements about Euglena is INCORRECT?

Accepted Answer

It reproduces exclusively by sexual reproduction — Euglenoids like Euglena reproduce by longitudinal binary fission (asexual reproduction) — sexual reproduction is not known. They are 'mixotrophic' — photosynthetic in light and heterotrophic when deprived of sunlight. The flexible pellicle (made of proteins) replaces a cell wall, allowing them to change shape.

Question 10

The bacteria Nostoc and Anabaena are important in agriculture because they:

Accepted Answer

Fix atmospheric nitrogen in specialised cells called heterocysts — Nostoc and Anabaena are filamentous cyanobacteria (blue-green algae) that fix atmospheric nitrogen in specialised, thick-walled cells called heterocysts. This makes them important biofertilisers in paddy fields. Cyanobacteria have chlorophyll a and are photosynthetic; some also form symbiotic associations (e.g., Anabaena in Azolla).