AQA GCSE Simple diffusion (Biology)

Simple diffusion

Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

Net movement means the overall movement. So, if 10 people get off of a bus and 4 people board the bus, then there is a net movement of 6 people off of the bus.

Why diffusion occurs.

At room temperature the particles in liquids or gases have energy, so they move in random directions.

Whilst moving the particles collide with each other and the walls of the container.

Gradually, they spread themselves out from area of high concentration to an area of low concentration.

Diffusion is described as an energy passive process. It does not need to have additional energy supplied to allow to occur.

An example of diffusion is if someone sprays a perfume in the corner of a room, gradually the perfume particles will spread themselves out throughout the room.

Diffusion and biological cells.

The cell membrane controls which substances enter and leaves the cell.

Substances can enter or leave the cell by moving across the cell membrane via diffusion.

Examples of substances that diffuse across the cell membrane include oxygen, glucose, carbon dioxide and urea.

Diffusion at the gas exchange surface

Oxygen will diffuse from the alveolus into the red blood cells at the gas exchange surface.

There is a high concentration of oxygen in alveolus and a low concentration of oxygen in red blood cells.

Carbon dioxide will diffuse from the red blood cells into the alveolus at the gas exchange surface.

There is a high concentration of carbon dioxide in the red blood cells and a low concentration of carbon dioxide in the alveolus.

Diffusion between blood and body tissues

Oxygen will diffuse from the red blood cells into the body cells for aerobic respiration. There is a higher concentration of oxygen in the red blood cells compared to the body cells.

Carbon dioxide will diffuse from the body cells into the red blood cells. Carbon dioxide is a waste product from respiration. There is a higher concentration of carbon dioxide in the body cells compared to the red blood cells.

Urea, which is a waste product from the breakdown of excess protein will diffuse from the body cells into the blood plasma. The blood plasma will transport the urea from the body cells to the kidneys where it is excreted.