1. Which process specifically describes net water movement across a partially permeable membrane?
- Transpiration
- Translation
- Osmosis
Check the answer and reasoning
Osmosis
Osmosis describes water movement; diffusion is a broader particle process.
Biology / IGCSE
Cells and movement across membranes
Tissues, organs and organ systems coordinate specialised cells.
Learning objectives
- Connect specialised cell structure with function.
- Distinguish diffusion, osmosis and active transport.
- Predict water movement between solutions.
The big idea
Tissues, organs and organ systems coordinate specialised cells. Diffusion is net particle movement down a concentration gradient; osmosis concerns water through a partially permeable membrane.
Active transport moves substances against a concentration gradient using energy from respiration. Plant cells become turgid when water enters against their walls, whereas animal cells lack this rigid support and can burst in sufficiently dilute surroundings.
Worked example
A cell’s mass rises from 2.0 g to 2.4 g after water enters. Find percentage increase.
Follow the solution
The increase is 0.4 g; 0.4/2.0×100=20%.
Investigate and explain
Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.
Related simplified PhET model. Explain what it represents and what the living system does differently.
Check your understanding
2. A cell’s mass rises from 2.0 g to 2.4 g after water enters. Find percentage increase.
- 20%
- 0.4%
- 120%
Check the answer and reasoning
20%
The increase is 0.4 g; 0.4/2.0×100=20%.
3. Does diffusion require every particle to move in one direction?
- Yes
- No
- Only in a liquid
Check the answer and reasoning
No
Particles move randomly both ways; unequal movement rates produce a net transfer.