Free Cell membranes & transport questions for AS Level Biology (9700), part of Cells & molecules. Each question has the answer and the marking points an examiner would look for.
Generate a full Cell Membranes & Transport worksheet →All Cells & molecules questionsWhich row matches the substance with its usual method of crossing a cell membrane?
| oxygen | glucose into red blood cells | sodium ions out of nerve cells | |
|---|---|---|---|
| A | osmosis | facilitated diffusion | active transport |
| B | facilitated diffusion | simple diffusion | active transport |
| C | simple diffusion | facilitated diffusion | active transport |
| D | simple diffusion | active transport | facilitated diffusion |
Answer: C
The fluid mosaic model describes membrane structure.
1 Cholesterol regulates membrane fluidity.
2 Channel proteins allow ions to cross by facilitated diffusion.
3 Carrier proteins used in active transport do not change shape.
Which statements are correct?
Answer: B
Which statement describes fluid mosaic model?
Answer: D
A plant cell has a solute potential of −700 kPa and a pressure potential of 400 kPa. It is placed in a solution with a water potential of −500 kPa.
What happens?
Answer: C
Potato discs are placed in sucrose solutions to find the water potential of the tissue. The discs show no change in mass in 0.2 mol dm−3 sucrose.
Explain why there is no change in mass in this solution.
Explain the change in mass of discs in a more dilute solution.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | same water potential the water potential of the tissue equals that of the solution B1 no net movement of water by osmosis B1 | 2 |
| (b) | gain mass, water enters by osmosis gain mass B1 water moves into cells by osmosis from higher water potential (solution) to lower (cells) B1 | 2 |
This question is about cell membranes and transport.
Describe the fluid mosaic model of membrane structure.
A plant cell with water potential -400 kPa is placed in a solution of water potential -200 kPa. State and explain the direction of net water movement.
Describe what happens to the cell if it is placed in a very concentrated sucrose solution, and explain why the cell wall does not shrink.
Explain how cholesterol affects the fluidity of membranes.
Distinguish between facilitated diffusion and active transport.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | phospholipid bilayer; hydrophilic heads out, hydrophobic tails in; proteins scattered (intrinsic, extrinsic); cholesterol; glycoproteins; molecules move laterally phospholipid bilayer with hydrophilic heads facing outwards and hydrophobic tails inwards B1 proteins (intrinsic and extrinsic) scattered like a mosaic B1 cholesterol, glycolipids and glycoproteins present B1 components move laterally (fluid) B1 | 4 |
| (b) | into the cell: solution has higher water potential water moves into the cell by osmosis B1 from higher (less negative) water potential in the solution to lower in the cell B1 | 2 |
| (c) | water lost, protoplast shrinks, plasmolysis; cell wall rigid cellulose, freely permeable water leaves by osmosis and the vacuole and cytoplasm shrink B1 the cell membrane pulls away from the wall (plasmolysis) B1 the cellulose wall is rigid / fully permeable, so sucrose solution fills the gap B1 | 3 |
| (d) | reduces fluidity at high temp, prevents too rigid at low temp cholesterol restricts phospholipid movement at higher temperatures B1 and prevents close packing (keeps fluid) at low temperatures B1 | 2 |
| (e) | both use membrane proteins; facilitated down gradient, no ATP; active against gradient, ATP, carrier proteins both use membrane proteins B1 facilitated diffusion moves substances down a concentration gradient without ATP (channel or carrier proteins) B1 active transport moves substances against the gradient using ATP and carrier proteins B1 | 3 |
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