GCSE Bio B2- transport and exchange

What is diffusion?

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. It occurs down a concentration gradient.

What factors affect the rate of diffusion?

The rate of diffusion is affected by:

1. Concentration gradient: A steeper gradient increases the rate.

2. Temperature: Higher temperature increases particle kinetic energy, increasing the rate.

3. Surface area: A larger surface area allows more particles to diffuse.

4. Distance/thickness of membrane: A shorter distance/thinner membrane increases the rate.

Give examples of diffusion in living organisms.

Examples of diffusion include:

• Gas exchange in the lungs: Oxygen diffuses from alveoli into the blood, carbon dioxide diffuses from blood into alveoli.

• Absorption of digested food: Small molecules (e.g., glucose, amino acids) diffuse from the small intestine into the blood.

• Urea diffusion: Urea diffuses from cells into the blood plasma to be transported to the kidneys.

What is osmosis?

Osmosis is the net movement of water molecules from an area of higher water potential (dilute solution) to an area of lower water potential (concentrated solution) across a partially permeable membrane.

What happens to animal cells in solutions of different water potentials?

1. In pure water/dilute solution (higher water potential): Water enters the cell, causing it to swell and potentially burst (lysis) as animal cells lack a cell wall.

2. In concentrated solution (lower water potential): Water leaves the cell, causing it to shrink and shrivel (crenation).