S4.1.3 For the adult
Diffusion, osmosis and active transport
A potato strip in plain water goes firm. In strong salt water it goes floppy. What is the water doing?
What this chapter teaches
Diffusion moves particles from a higher to a lower concentration. Osmosis moves water across a partially permeable membrane from a dilute to a more concentrated solution. Active transport moves particles from a lower to a higher concentration and uses energy from respiration.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does a potato strip in strong salt water go floppy?
- Which of diffusion, osmosis and active transport needs energy, and why?
- A strip goes from 50 mm to 45 mm. What is the percentage change?
After the chapter, the learner can
- Explain osmosis using potato pieces in salty and plain water
- Compare diffusion, osmosis and active transport
What they copy into their notebook
Diffusion: any particles, high to low, no energy. Osmosis: water, dilute to concentrated, through a partially permeable membrane. Active transport: low to high, uses energy from respiration. Percentage change = change ÷ start × 100.