Key learning points

1. All substances, including the cell cytoplasm and substances within it, are made up of particles.
2. These particles move in random directions and collide all the time.
3. Concentration is the number of particles in a volume of liquid or gas.
4. The net movement of particles is down a concentration gradient.
5. Diffusion is the passive movement of particles of a substance from an area of higher to lower concentration.

Keywords

• Passive process - A passive process doesn’t require any additional energy.

• Concentration - Concentration is the number of particles in a volume of liquid or gas.

• Concentration gradient - A concentration gradient is a difference in the concentration of particles from one area to another.

• Net movement - Net movement is the overall movement of particles from one area to another.

• Diffusion - Diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration.

Common misconception