NUMS — Medical & Dental Entry Test
Take the NUMS Biology — Cell Structure and Function (Set 5): 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 spherical cell of radius 5 μm grows to a radius of 15 μm. By what factor does its surface area to volume ratio change?
Answer: D. It falls to one-third
Explanation: SA:V of a sphere = 3/r. Tripling the radius makes the ratio one-third of its original value.
Q2. An electron micrograph is printed so that a mitochondrion of true length 1.5 μm measures 45 mm in the picture. What is the magnification?
Answer: D. ×30,000
Explanation: 45 mm = 45,000 μm; magnification = image size ÷ actual size = 45,000 ÷ 1.5 = 30,000.
Q3. A scale bar on a micrograph is 20 mm long and is labelled 2 μm. A nucleolus on the same picture measures 35 mm across. What is its real diameter?
Answer: B. 3.5 μm
Explanation: Each 10 mm of picture equals 1 μm, so 35 mm represents 3.5 μm.
Q4. Onion epidermal cells are placed in sucrose solutions. Plasmolysis is seen in 0% of cells at 0.2 M and 0.3 M, 50% at 0.4 M, and 100% at 0.5 M. What is the best conclusion about cells in 0.4 M sucrose?
Answer: B. Water potential equals the solution's and pressure potential is about zero
Explanation: The 50% point is incipient plasmolysis: no net water movement, so cell water potential equals that of the solution, and the wall is just no longer pushing back (pressure potential about zero).
Q5. A plant cell has solute potential −0.8 MPa and pressure potential +0.3 MPa. It is placed in a solution of water potential −0.3 MPa. What happens?
Answer: D. Water enters the cell, since its water potential is −0.5 MPa
Explanation: Cell ψ = ψs + ψp = −0.8 + 0.3 = −0.5 MPa, lower than the solution's −0.3 MPa, so water moves into the cell.
Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.
Q6. Uptake of a sugar into a cell is measured at increasing external concentrations. The rate rises steeply at first and then levels off at a maximum. Which transport mechanism fits this behaviour best?
Q7. The sodium–potassium pump exports 3 Na⁺ and imports 2 K⁺ for every ATP used. When 15 Na⁺ ions are pumped out, how many K⁺ ions are pumped in?
Q8. Root hair cells accumulate nitrate against its concentration gradient. When the roots are treated with cyanide, which result would be expected?
Q9. In cystic fibrosis, a defective chloride channel in epithelial cells leads to thick, sticky mucus. Which statement best explains the link?
Q10. A baby lacks a lysosomal hydrolase that normally breaks down a membrane lipid, and the lipid builds up in nerve cells. Which statement describes the underlying cause?
Q11. A cell biologist adds hydrogen peroxide to liver homogenate and observes vigorous bubbling that stops when the homogenate is boiled first. The bubbling comes from
Q12. Liver homogenate is spun in stages. A pellet is found to have high succinate dehydrogenase activity but no DNA. The pellet most probably contains
Q13. A drug stops transport vesicles from budding off the rough ER. Newly made secretory proteins would most probably
Q14. Chloramphenicol blocks protein synthesis on 70S ribosomes. Which cell components would it be expected to affect in a human cell?
Q15. A cell has a very large, darkly stained nucleolus. What does this indicate about the cell?
Q16. Which molecules are made in the cytoplasm but must be imported into the nucleus through nuclear pores?
Q17. Colchicine binds tubulin and prevents microtubule assembly. Dividing cells treated with colchicine are most likely to
Q18. Men with a defect in the dynein arms of the 9+2 axoneme often have chronic respiratory infections and infertility. Which pair of structures fails to move normally?
Q19. A pair of centrioles lies near the nucleus of an animal cell. Each centriole is a cylinder of nine microtubule triplets. How many microtubules are in the pair?
Q20. To obtain individual plant cells from a piece of tissue, a technician uses pectinase. Which structure does this enzyme mainly degrade?
Q21. Heart muscle cells contract almost in unison because an action potential passes quickly from cell to cell. Which junction type makes this possible?
Q22. Cell P has a cellulose wall, a large central vacuole, chloroplasts and 80S ribosomes. Cell Q has a peptidoglycan wall, 70S ribosomes and a circular chromosome. Which statement is correct?
Q23. A freshwater Paramecium is transferred from pond water to a moderately salty solution. What change is expected in its contractile vacuole?
Q24. Liver cells of patients with high cholesterol levels in blood fail to remove LDL particles because their LDL receptors are absent. Which process is impaired?
Q25. A pancreatic acinar cell secretes enzymes constantly, and its plasma membrane area stays nearly constant. What explains this?
Q26. Cold-adapted fish have more unsaturated phospholipids in their membranes than tropical fish. What is the advantage?
Q27. Blood group A and blood group B red cells differ only in the sugar chains carried on the outer face of their membranes. Which feature is described?
Q28. A potato tuber stored in light slowly turns green near the surface. Which change in its plastids explains this?
Q29. A red blood cell and a plant cell are both placed in distilled water. The red cell bursts, but the plant cell only becomes firm. Why does the plant cell not burst?
Q30. People who take certain sedatives for a long time often show a large increase in smooth ER in liver cells. Which role of the smooth ER accounts for this?