This worked example covers Surface Area to Volume Ratio within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 13 of 19 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🧮 Surface Area to Volume Ratio
Why is this ratio important?
As organisms get larger, their surface area to volume ratio gets smaller. This creates problems:
- Less surface area per unit volume for exchange
- Inner cells become too far from the surface
- Simple diffusion becomes too slow
- Need for specialized exchange surfaces and transport systems
📝 Calculation Example: Cube
For a 2cm cube:
- Surface area = 6 × side² = 6 × 4 = 24 cm²
- Volume = side³ = 2³ = 8 cm³
- Ratio = 24:8 = 3:1
For a 4cm cube:
- Surface area = 6 × 16 = 96 cm²
- Volume = 64 cm³
- Ratio = 96:64 = 1.5:1
Notice: Larger cube has smaller ratio!
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.
Quick recall flashcards
Define osmosis
The movement of water molecules from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration) through a semi-permeable membrane.
Define diffusion
The movement of particles from an area of high concentration to an area of low concentration down a concentration gradient. No energy is required (passive process).