NUMS — Medical & Dental Entry Test
Take the NUMS Biology — Cell Structure and Function (Set 4): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review.…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. A transmission electron micrograph shows a mitochondrion measuring 45 mm in length. If its actual length is 15 μm, what is the magnification?
Answer: B. ×3000
Explanation: Magnification = image size ÷ actual size = 45 mm ÷ 15 μm = 45 000 μm ÷ 15 μm = 3000.
Q2. A cell measures 3.5 cm across on a photomicrograph printed at ×2000. What is its actual diameter?
Answer: A. 17.5 μm
Explanation: Actual size = 3.5 cm ÷ 2000 = 35 000 μm ÷ 2000 = 17.5 μm.
Q3. Two cubical cells have sides of 2 μm and 4 μm. Which statement about their surface-area-to-volume (SA:V) ratios is correct?
Answer: B. The 2 μm cell has SA:V = 3 and the 4 μm cell has 1.5
Explanation: For a cube SA:V = 6a²/a³ = 6/a: 6/2 = 3 and 6/4 = 1.5. Larger cells have lower SA:V, limiting exchange.
Q4. Potato cylinders are weighed, soaked in sucrose solutions for an hour and reweighed. Mass change: 0.0 M = +12%; 0.2 M = +6%; 0.4 M = −6%; 0.6 M = −12%. Assuming a straight-line trend, the sucrose concentration isotonic to the potato cells is about
Answer: D. 0.3 M
Explanation: Zero mass change lies midway between +6% (0.2 M) and −6% (0.4 M), i.e. 0.3 M, where there is no net water movement.
Q5. A plant cell has solute potential −0.9 MPa and pressure potential +0.5 MPa. It is placed in a solution of water potential −0.6 MPa. What happens?
Answer: A. Net water movement out of the cell, because the cell's water potential is −0.4 MPa
Explanation: Ψcell = Ψs + Ψp = −0.9 + 0.5 = −0.4 MPa, which is higher (less negative) than −0.6 MPa, so water moves down the gradient out of the cell. Using Ψs alone is the common trap.
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Q6. A plant cell at incipient plasmolysis is placed in a solution and no net water movement occurs. Which of the following must be true of the cell?
Q7. Cholesterol is removed from the plasma membrane of cultured cells and they are warmed from 20 °C to 40 °C. Compared with normal cells, the membrane will be
Q8. A Na⁺/K⁺ pump of a nerve cell uses 30 ATP molecules. How many ions are moved, and what is the net charge change inside the cell?
Q9. A pulse of radioactive amino acids is given to pancreatic cells and followed with unlabelled amino acids. Which sequence shows where labelled insulin precursor is found over time?
Q10. A child lacks one lysosomal hydrolase and substrate builds up inside cells, enlarging them. This type of disease arises because
Q11. Catalase in peroxisomes converts H₂O₂ to water and oxygen (2H₂O₂ → 2H₂O + O₂). If 34 g of H₂O₂ is completely decomposed, what mass of O₂ is released? (H = 1, O = 16)
Q12. Two cell types are compared: type X has abundant mitochondria with densely packed cristae; type Y has few mitochondria with sparse cristae. Which is the most reasonable inference?
Q13. Liver homogenate is centrifuged at low speed and the pellet is examined first. Which structures are most likely in this first pellet?
Q14. Streptomycin binds bacterial 70S ribosomes. Why can it still cause side effects in humans?
Q15. Which statement about ribosomal subunits is correct?
Q16. A drug prevents actin filaments from assembling. Dividing cells treated with it complete mitosis but become binucleate. Which process is blocked?
Q17. In cross-section, an electron micrograph shows a cylinder with 9 outer pairs of microtubules and 2 central single microtubules. This structure is
Q18. A patient's cells cannot take up LDL cholesterol from blood, leaving blood cholesterol high. This is most directly a defect in
Q19. The rate of uptake of a nutrient by cells increases with concentration and then levels off. Adding cyanide (which blocks ATP production) stops uptake completely. The transport is
Q20. A fruit softens and its cells separate easily when calcium pectate in its tissue is broken down. Which structure is being degraded?
Q21. Cardiac muscle cells contract almost simultaneously because ions pass directly from one cell to the next. Which junction mainly supports this?
Q22. Carrot roots are orange although they are underground. Which plastid gives the colour?
Q23. A plant cell is placed in a hypertonic solution and its central vacuole shrinks. Which membrane surrounds the vacuole and controls this water movement?
Q24. Cells of one tissue show a very large nucleolus and abundant free ribosomes, and the tissue is growing fast. Which activity is emphasised?
Q25. Viruses are acellular, so they fall outside the cell theory. Which statement of the theory do they fail to fit because they are not made of cells?
Q26. A light microscope has a resolving power of about 0.2 μm. Which structure pair could both be resolved? (ribosome ≈ 25 nm, mitochondrion ≈ 1000 nm wide, plasma membrane ≈ 8 nm thick, nucleus ≈ 5000 nm)
Q27. Cells in a tissue section show abundant smooth ER and mitochondria with tubular cristae, and the cells secrete lipid-soluble hormones. The tissue is most likely
Q28. The acrosome of a sperm, which contains hydrolytic enzymes, is derived from which organelle?
Q29. A protein is made on free ribosomes and remains in the cytosol, whereas a similar protein is made on the rough ER. Which feature most directly decides this?
Q30. Which observation is the strongest support for the endosymbiotic origin of mitochondria?