3.5 Diffusion

Question 1

What is diffusion?

Answer 1

The net (overall) movement of particles from an area of higher concentration to an area of lower concentration

Question 2

Cell membranes are partially permeable. What does this mean?

Answer 2

Only very small molecules can move through them - things like glucose, amino acids, water and oxygen. Things like starch, sucrose, and proteins cant fit through

Question 3

Is diffusion a passive or an active process? what does this mean?

Answer 3

Passive, this means it doesn’t require any energy from the cells

Question 4

What are the 3 factors that affect the rate of diffusion?

Answer 4

• Concentration gradient: the larger the concentration gradient, the higher the rate of diffusion
• Temperature: higher temperatures give the particles more energy so they move around faster, this means they diffuse faster
• Surface area: larger surface area, higher rate of diffusion

Question 5

Describe the steps to investigate diffusion in a non-living system (3)

Answer 5

Phenolphthalein is a pH indicator - it’s pink in alkaline solution and colourless in acidic solutions. You can use it to investigate diffusion in agar jelly:
1) First, you need some agar jelly made from phenolphthalein and dilute sodium hydroxide. Dilute sodium hydroxide is an alkali, so the jelly should be pink.
2) Now, add some dilute hydrochloric acid to a beaker. Measure out and cut some cubes from the jelly - then put them in the beaker of acid.
3) If the cubes are left they’ll eventually turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide - use a stopwatch to see how long it takes. You could investigate how varying the concentration of the acid (e.g. between 0.1 and 1M) affects the rate of diffusion. Keep everything apart from the concentration of acid the same.