24 free Biology MCQs written in the NEET exam pattern, each with a step-by-step solution. Tap an option for instant feedback — no sign-up, no ads.
Revise with smart repetition →✍️ These are original practice questions written in the NEET pattern for the NEET (UG) medical entrance exam — not questions from any official past paper.
Q1. In a eukaryotic cell, the Krebs (citric acid) cycle takes place in the:
B. Mitochondrial matrix — The Krebs cycle occurs in the mitochondrial matrix. Glycolysis happens in the cytoplasm, and the light-independent reactions of photosynthesis occur in the chloroplast stroma — so those options are incorrect.
Q2. The natural pacemaker of the human heart is the:
C. Sinoatrial (SA) node — The sinoatrial (SA) node in the wall of the right atrium generates the impulses that set the heart's rhythm, so it is called the pacemaker. The AV node, bundle of His and Purkinje fibres conduct that impulse onward to the ventricles.
Q3. The structural and functional unit of the human kidney is the:
A. Nephron — Each kidney contains about a million nephrons, which filter blood and form urine. A neuron is a nerve cell, an alveolus is an air sac in the lung, and a villus is a projection of the intestinal lining.
Q4. Which nitrogenous base is present in RNA but absent in DNA?
D. Uracil — RNA contains uracil in place of the thymine found in DNA. Adenine and guanine are purines present in both DNA and RNA, so they are not the answer.
Q5. In vascular plants, water and dissolved minerals are conducted upward from the roots mainly by the:
B. Xylem — Xylem conducts water and minerals upward from the roots to the rest of the plant. Phloem translocates the sugars made in photosynthesis; the cambium is a meristem; the epidermis is a protective covering.
Q6. Insulin, the hormone that lowers blood glucose, is secreted by the:
C. Beta cells of the islets of Langerhans — The beta cells of the islets of Langerhans in the pancreas secrete insulin, which lowers blood glucose. The alpha cells secrete glucagon, which raises blood glucose — the opposite effect.
Q7. Ribosomes in a cell are the site of:
B. Protein synthesis — Ribosomes translate mRNA into polypeptides, so they are the site of protein synthesis. DNA replication occurs in the nucleus in eukaryotes; photosynthesis occurs in chloroplasts.
Q8. Double fertilisation — one male gamete fusing with the egg and the other with the polar nuclei — is a characteristic feature of:
D. Angiosperms — Double fertilisation — syngamy (male gamete + egg → zygote) plus triple fusion (male gamete + two polar nuclei → endosperm) — occurs only in angiosperms (flowering plants). Gymnosperms show single fertilisation.
Q9. Which of the following cell organelles is bounded by only a single membrane?
A. Lysosome — Lysosomes are surrounded by a single unit membrane, whereas mitochondria, chloroplasts and the nucleus are each enclosed by a double membrane (envelope).
Q10. A heterozygous tall pea plant (Tt) is crossed with a homozygous dwarf plant (tt). The expected phenotypic ratio of tall to dwarf offspring is:
B. 1 : 1 — This is a test cross (Tt x tt). It yields half Tt (tall) and half tt (dwarf), giving a 1 : 1 phenotypic ratio.
Q11. During DNA replication, Okazaki fragments are synthesised discontinuously on the:
B. Lagging strand — Because DNA polymerase works only 5' to 3', the strand oriented opposite to the replication fork movement (the lagging strand) is made as short Okazaki fragments that are later joined by ligase.
Q12. Bile secreted by the liver aids fat digestion mainly by:
A. Emulsifying large fat globules into smaller droplets — Bile contains no digestive enzymes; its salts emulsify fats into fine droplets, increasing the surface area for pancreatic lipase to act on.
Q13. The largest fraction of carbon dioxide is transported in human blood in the form of:
C. Bicarbonate ions — About 70% of CO2 is carried as bicarbonate (HCO3-) ions formed in RBCs by carbonic anhydrase; roughly 20-25% is carbaminohaemoglobin and only about 7% is dissolved in plasma.
Q14. The rising (depolarisation) phase of an action potential in a neuron is caused mainly by the rapid influx of:
D. Sodium ions — When a threshold stimulus opens voltage-gated Na+ channels, Na+ rushes in and reverses the membrane polarity, producing the depolarisation (rising) phase of the action potential.
Q15. In the light reactions of photosynthesis, the photolysis (splitting) of water is closely associated with:
A. Photosystem II — Water is split on the inner thylakoid side in association with Photosystem II, releasing electrons (to replace those lost by P680), protons, and O2.
Q16. According to Lindeman's ten percent law, roughly 10% of the energy at one trophic level is:
C. Transferred to the next higher trophic level — The ten percent law states that only about 10% of the energy captured at one trophic level is passed on to (and stored by) organisms at the next higher trophic level; the rest is lost mainly as heat.
Q17. The DNA sequences recognised by restriction endonucleases used in genetic engineering are usually:
B. Palindromic sequences — Restriction enzymes recognise specific palindromic sequences (reading the same 5' to 3' on both strands) and cut within or near them, often producing sticky ends.
Q18. A mid-cycle surge of which hormone directly triggers ovulation in the human female?
A. Luteinising hormone (LH) — A sharp rise (surge) in LH around mid-cycle induces rupture of the mature Graafian follicle and release of the ovum (ovulation).
Q19. The wings of a butterfly and the wings of a bird are best described as:
B. Analogous organs — Both perform the same function (flight) but differ in structure and origin, making them analogous organs, an example of convergent evolution.
Q20. A competitive inhibitor decreases the rate of an enzyme-catalysed reaction because it:
B. Structurally resembles the substrate and competes for the active site — A competitive inhibitor closely resembles the substrate and occupies the active site, blocking substrate binding; its effect can be overcome by raising substrate concentration.
Q21. Mature sieve tube elements of angiosperm phloem lack a nucleus yet stay functional because their activities are controlled by adjacent:
C. Companion cells — Each enucleate sieve tube element is connected through plasmodesmata to a nucleated companion cell, which maintains the sieve tube's metabolic functions.
Q22. A water vascular system with tube feet used for locomotion is a distinctive feature of the phylum:
D. Echinodermata — Echinoderms (e.g., starfish) possess a unique water vascular system with tube feet used for locomotion, food capture and respiration.
Q23. The antibody present in a mother's colostrum that provides passive immunity to the breastfed newborn is:
D. IgA — Colostrum, the early milk, is rich in secretory IgA, which protects the infant's gut mucosa and confers passive immunity.
Q24. Which hormone raises blood calcium levels chiefly by stimulating resorption of calcium from bone?
C. Parathyroid hormone — Parathyroid hormone (parathormone) increases blood Ca2+ by promoting bone resorption and renal reabsorption of calcium; calcitonin has the opposite (calcium-lowering) effect.
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