This memory aid covers Memory Aid: DOA within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 16 of 19 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
💡 Memory Aid: DOA
Use the acronym DOA to remember the three transport types and their key features:
| Letter | Process | Key Feature | Energy? |
|---|---|---|---|
| D | Diffusion | Down the gradient (high → low), any particle | No |
| O | Osmosis | Only water, through partially permeable membrane | No |
| A | Active transport | Against the gradient (low → high), needs ATP | Yes |
Additional Mnemonics
- Osmosis = O — "O" looks like water droplets. Osmosis = water ONLY. "O for Only water."
- Active = Against — Both start with "A". Active transport goes Against the gradient.
- Turgid, Flaccid, Plasmolysed — "The Full Plant Plays" → Turgid (full of water), Flaccid (limp), Plasmolysed (pulled away from wall).
- Percentage change formula — "Final minus Initial, divided by Initial, times 100." Think: "FI-I over I times 100."
Quick Check: Explain why a lettuce leaf placed in salty water becomes limp and wilts. Use the terms osmosis, partially permeable membrane, concentration gradient, and flaccid in your answer.
The salty water has a lower water concentration (higher solute concentration) than the cytoplasm inside the lettuce cells. Water therefore moves by osmosis — through the partially permeable cell membrane — down the water concentration gradient, out of the cells and into the salty solution. As the cells lose water, their vacuoles shrink and they become flaccid (limp). With no turgor pressure pushing against the cell walls, the leaf loses its rigidity and wilts.
Practice questions for Cell Transport
Which statement best describes diffusion?
Explain how osmosis causes a plant cell to become plasmolysed when placed in a concentrated sugar solution.