B4 - Diffusion and Osmosis

Question 1

What is diffusion ?

Answer 1

Particles moving from an area of high concentration to an area of low concentration. They move until they are evenly spread.

Question 2

What can affect the rate of diffusion and why?

Answer 2

Distance - the shorter the distance, the quicker the rate of diffusion.

Concentration gradient - the greater the difference in concentration between two regions, the fastest the rate of diffusion.

Surface area - the greater the surface area that the particles have to diffuse across, the quicker the rate of diffusion.

Question 3

What is osmosis?

Answer 3

The movement of water from an area of high concentration to an area of low concentration through a semi - permeable membrane

Question 4

What happens in plant cells in different concentrations?

Answer 4

• dilute solution -> takes up water by osmosis, pressure in cell increases, becomes turgid
• isotonic solution-> no net movement of water
• more concentrated solution -> loses water by osmosis, becomes flaccid. Eventually the cells contents collapse away from the cell wall - plasmolysed cell

Question 5

What happens in animal cells in different concentrations ?

Answer 5

• dilute solution - takes up water, swells and may burst - lysis
• isotonic - no net movement of water
• more concentrated solution - loses water by osmosis, becomes crenated