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S4 Biology Membranes and Transport, Paper 1: diffusion, osmosis and active transport
S4 Biology Membranes and Transport, Paper 1: diffusion, osmosis and active transport
Paper 1 works through mass-change percentages, water potential, plasmolysis and the energy cost of active transport.
Focus Water always moves from high to low water potential, and only active transport spends ATP.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Biology: Membranes and Transport |
| Level | S4 |
02 Questions (10 items)
- FoundationIn which direction does diffusion take place?
- FoundationA potato strip grows from 2.0 g to 2.3 g. What is the percentage increase?
- FoundationBetween 0.2 M and 0.5 M sucrose, which way does water move?
- FoundationDefine osmosis.
- IntermediateWhat happens to a plant cell placed in 1.0 M sucrose?
- IntermediateFor a cube of side 2 cm, what is the surface area to volume ratio?
- IntermediateHow does active transport differ from passive transport?
- ChallengeThree strips change by minus three per cent, nothing and plus four per cent. Which solution is isotonic?
- ChallengeA substance diffuses at 0.02 mm per second. How long to travel 0.1 mm?
- Error redoError: a student says osmosis moves water from low to high water potential. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | From higher to lower concentration until balanced | Particles move randomly, so the net flow runs from high to low concentration. |
| 2 | Fifteen per cent | The gain of 0.3 g divided by 2.0 g gives 0.15, or fifteen per cent. |
| 3 | Towards the 0.5 M solution | The stronger solution has the lower water potential, so water enters it. |
| 4 | Water moving through a partially permeable membrane from higher to lower water potential | Only water crosses this membrane, so it flows towards the side with more solute. |
| 5 | Plasmolysis, with the membrane pulling away from the wall | The cell loses water and shrinks, so the membrane pulls away from the wall. |
| 6 | 3 per cm | Surface area is 24 and volume is 8, so the ratio is 3. |
| 7 | Active moves against the gradient and needs ATP; passive follows the gradient without ATP | Active transport uses carrier proteins and ATP, so ions can be pumped against the gradient. |
| 8 | The one with no change | No change in mass means water enters and leaves equally, so that solution is isotonic. |
| 9 | 5 seconds | Dividing 0.1 by 0.02 gives 5, and the time grows with the distance. |
| 10 | Water moves from high potential, in pure water, to low potential in the solution | The direction is reversed: pure water has the highest potential and water always flows down. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.
