A-Level Biology Topic 4: Cell Membranes and Transport MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Practice for Cambridge International AS and A Level Biology 9700, Topic 4, covering the fluid mosaic model, movement across membranes, water potential and cell signalling, with a short explanation after every question.
The Fluid Mosaic Model
Q1. In the fluid mosaic model, how are phospholipids arranged in a membrane?
- (A) As a single layer with tails facing outwards into the water
- (B) As a rigid wall of protein only
- (C) As a bilayer, heads outwards and tails inwards
- (D) As scattered droplets with no pattern
Show Answer
Answer: C – Hydrophilic heads face the watery surroundings on both sides, while hydrophobic tails face each other in the middle of the bilayer.
Q2. Why is the membrane described as fluid?
- (A) Its phospholipids and proteins can move sideways
- (B) It dissolves completely in water around the cell surface
- (C) It has no proteins
- (D) It is made only of water
Show Answer
Answer: A – Phospholipid molecules and many proteins can move laterally, so the membrane is flexible rather than rigid.
Q3. What role does cholesterol play in a cell surface membrane?
- (A) It transports glucose actively across the membrane using ATP
- (B) It helps maintain stability and fluidity of the membrane
- (C) It forms the cell wall
- (D) It produces ATP
Show Answer
Answer: B – Cholesterol molecules fit between phospholipids and help keep the membrane stable yet fluid.
Q4. Which membrane proteins allow water-soluble substances to cross the membrane?
- (A) Glycolipids only
- (B) Cholesterol molecules only
- (C) Peripheral proteins on the surface only, not spanning it
- (D) Channel and carrier proteins spanning the membrane
Show Answer
Answer: D – Channel proteins form pores and carrier proteins change shape to move substances across the membrane.
Q5. What is a glycoprotein in a cell surface membrane?
- (A) A protein with a carbohydrate chain attached
- (B) A lipid with no carbohydrate attached to it at all
- (C) A protein found only inside the nucleus
- (D) A carbohydrate stored in the vacuole
Show Answer
Answer: A – Glycoproteins are proteins with carbohydrate chains attached, and they act in cell recognition and signalling.
Q6. What are cell surface antigens used for?
- (A) Producing ATP
- (B) Digesting proteins in the cytoplasm of the cell
- (C) Allowing cells to recognise self and non-self
- (D) Forming the nuclear envelope
Show Answer
Answer: C – Cell surface antigens, often glycoproteins, allow the immune system and other cells to recognise cell identity.
Q7. Which statement about the phospholipid bilayer is correct?
- (A) It is fully permeable to all substances in solution
- (B) It is partially permeable to different substances
- (C) It blocks water completely
- (D) It lets large proteins diffuse freely
Show Answer
Answer: B – The bilayer is partially permeable: small non-polar molecules cross easily, while ions and large polar molecules need proteins or other routes.
Q8. What is a glycolipid?
- (A) A protein channel
- (B) A cholesterol molecule
- (C) A nucleic acid in the membrane of the cell
- (D) A lipid with a carbohydrate chain attached
Show Answer
Answer: D – Glycolipids are lipids with attached carbohydrate chains, found on the outer surface of the membrane, where they help with recognition.
Q9. In cell signalling, what is a ligand?
- (D) A molecule of ATP inside a mitochondrion
- (B) A type of cell wall
- (C) A channel protein that never closes
- (A) A chemical secreted by one cell that binds to a receptor on a target cell
Show Answer
Answer: D – A ligand is a signalling chemical released by one cell that travels to a target cell and binds its receptor.
Q10. What happens after a ligand binds to a cell surface receptor?
- (A) The cell always divides at once
- (B) The receptor is destroyed permanently
- (C) A specific response is triggered in the target cell
- (D) The ligand enters the nucleus and becomes part of the DNA
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Answer: C – Binding of a ligand to its receptor triggers a chain of events leading to a specific response in the target cell.
Diffusion, Facilitated Diffusion and Active Transport
Q11. What is simple diffusion?
- (A) Movement of molecules against a concentration gradient, using ATP
- (B) Movement of water through a partially permeable membrane
- (C) Bulk movement of large particles in vesicles
- (D) Net movement of molecules down a gradient without energy
Show Answer
Answer: D – Simple diffusion is the passive, net movement of molecules from a region of higher concentration to a region of lower concentration.
Q12. How does facilitated diffusion differ from simple diffusion?
- (A) It uses ATP directly
- (B) It uses channel or carrier proteins down a gradient
- (C) It moves substances against a concentration gradient
- (D) It only moves water
Show Answer
Answer: B – Facilitated diffusion uses membrane proteins to help substances cross, but it remains passive movement down a concentration gradient.
Q13. Which process moves ions against their concentration gradient?
- (A) Active transport, using ATP
- (B) Simple diffusion down a concentration gradient
- (C) Facilitated diffusion
- (D) Osmosis
Show Answer
Answer: A – Active transport uses energy from ATP to move substances against a concentration gradient, through carrier proteins.
Q14. What is endocytosis?
- (A) Release of substances from a cell in vesicles that fuse with the membrane
- (B) Diffusion of oxygen into a cell
- (C) Uptake of substances into a cell in vesicles formed from the membrane
- (D) Active transport of single ions
Show Answer
Answer: C – In endocytosis, the membrane folds around material and pinches off to form a vesicle inside the cell.
Q15. What is exocytosis?
- (A) Uptake of bacteria by a white blood cell in a vesicle formed from it
- (B) Movement of water into a root hair cell
- (C) Diffusion through a channel protein
- (D) Release of substances when a vesicle fuses with the membrane
Show Answer
Answer: D – In exocytosis, a vesicle fuses with the cell surface membrane and releases its contents outside the cell.
Q16. Why does a steeper concentration gradient increase the rate of diffusion?
- (A) More molecules move from higher to lower concentration
- (B) The membrane becomes fully permeable
- (C) ATP production increases in the mitochondria of the cell
- (D) The molecules become smaller
Show Answer
Answer: A – A larger difference in concentration means a greater net movement of molecules down the gradient.
Q17. Which factor would increase the rate of diffusion across a membrane?
- (A) A smaller surface area for diffusion to occur across it
- (B) A larger surface area and shorter diffusion distance
- (C) A lower temperature
- (D) A thicker membrane
Show Answer
Answer: B – A larger surface area provides more space for movement, and a shorter distance means molecules cross faster.
Q18. Visking tubing is used in investigations of diffusion because it acts as what?
- (A) A source of ATP for active transport
- (B) A living cell
- (C) A partially permeable membrane
- (D) A carrier protein
Show Answer
Answer: C – Visking tubing is a non-living, partially permeable membrane that allows small molecules through but holds back larger ones.
Q19. In an agar block investigation, why does a smaller block change colour faster throughout?
- (A) It has a larger surface area to volume ratio
- (B) It has more cells in its outer layers than a large block
- (C) It produces ATP faster
- (D) It has a thicker outer layer
Show Answer
Answer: A – Smaller blocks have a larger surface area relative to their volume, so diffusion reaches the centre sooner.
Q20. As an organism or cell grows larger, what happens to its surface area to volume ratio?
- (A) It increases
- (B) It stays exactly the same as the cell grows larger in size
- (C) It decreases, as volume grows faster than surface area
- (D) It becomes infinite
Show Answer
Answer: C – Surface area grows with the square of length while volume grows with the cube, so the ratio falls as size increases.
Osmosis, Water Potential and Cell Responses
Q21. What is osmosis?
- (A) Water moving down a water potential gradient
- (B) Net movement of solutes down a concentration gradient
- (C) Active transport of water using ATP
- (D) Bulk uptake of water in vesicles
Show Answer
Answer: A – Osmosis is the diffusion of water through a partially permeable membrane, from higher to lower water potential.
Q22. A plant cell is placed in pure water. In which direction does water move?
- (A) Out of the cell only
- (B) Neither in nor out
- (C) Into the cell, as pure water has higher water potential
- (D) Into the vacuole only, bypassing the cytoplasm entirely
Show Answer
Answer: C – Water moves by osmosis from the higher water potential of pure water into the lower water potential inside the cell.
Q23. What happens to a plant cell placed in pure water?
- (A) It bursts
- (B) It becomes turgid, with the wall resisting further expansion
- (C) It becomes plasmolysed
- (D) It shrinks away from its wall as water leaves the cell by osmosis
Show Answer
Answer: B – Water enters the plant cell, but the strong cell wall prevents bursting, so the cell becomes turgid.
Q24. What happens to an animal cell placed in pure water?
- (A) It becomes turgid as water enters the cell by osmosis
- (B) It becomes plasmolysed
- (C) It stays the same size
- (D) It swells and may burst, since it has no cell wall
Show Answer
Answer: D – Water enters by osmosis and, without a wall to resist expansion, the animal cell swells and may burst.
Q25. What happens to a plant cell placed in a concentrated solution?
- (A) It becomes turgid
- (B) Water leaves and cytoplasm pulls away from the wall
- (C) Water enters and the cell bursts as pressure rises greatly
- (D) Nothing changes
Show Answer
Answer: B – Water leaves the cell by osmosis, the vacuole shrinks and the cytoplasm pulls away from the cell wall, a state called plasmolysis.
Q26. What happens to an animal cell placed in a concentrated solution?
- (A) It swells and bursts as water enters the cell
- (B) It loses water and shrinks
- (C) It becomes turgid
- (D) It gains a cell wall
Show Answer
Answer: B – Water leaves the animal cell by osmosis towards the lower water potential outside, so the cell shrinks.
Q27. How can the water potential of plant tissue be estimated?
- (A) By counting its cells
- (B) Finding the solution where tissue mass does not change
- (C) By measuring its colour before and after immersion in solution
- (D) By weighing it once in air
Show Answer
Answer: B – The solution where the tissue neither gains nor loses mass has the same water potential as the tissue.
Q28. What are the main stages of cell signalling in order?
- (D) Transport to a target cell, then secretion of a ligand
- (B) Binding to a receptor, secretion of a ligand, then transport
- (C) A specific response, then secretion of a ligand
- (A) Secretion of a ligand, transport to a target cell, binding to a receptor, then a specific response
Show Answer
Answer: D – Signalling starts with secretion of a specific chemical, its transport to target cells, binding to receptors and then a response.
Q29. Why does a signalling chemical usually affect only certain target cells?
- (A) Only target cells have the matching receptor
- (B) Only target cells contain water in their cytoplasm
- (C) Only target cells have a cell wall
- (D) Only target cells can carry out diffusion
Show Answer
Answer: A – A ligand only triggers a response in cells carrying the receptor that matches it.
Q30. Which investigation uses plant tissue to study osmosis?
- (A) Measuring mass change of potato in different solutions
- (B) Measuring oxygen released by catalase in a reaction mixture
- (C) Counting ribosomes in an electron micrograph
- (D) Testing for starch with iodine
Show Answer
Answer: A – Changes in mass of plant tissue in different solutions show whether water has entered or left by osmosis.
Work through any questions you missed again, then revise those areas before moving on to the next topic.