DIFFUSION

Smells, for example, travel by diffusion. Particles in gases and liquids are constantly moving past each other in random directions, but the particles will always move from an area of high concentration to an area of low concentration, or in adherence with the concentration gradient. This is a passive process and does not require energy.

OSMOSIS

A membrane that allows some molecules through it and not other is partially permeable. Osmosis is the net movement of water molecules from an area of high water concentration to an area of low water concentration through a partially permeable membrane.

ACTIVE TRANSPORT

Cells may need to transport molecules against the concentration gradient, or transport molecules that are too big to diffuse through a membrane. They do this using active transport. This process is carried out by proteins in the cell membrane. This is an active process (says so in the name) and requires energy in the form of ATP.

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Slide Set on Edexcel 9-1 GSCE Biology B1 Summary; Key Concepts in Biology., created by Fatima Hussain on 21/04/2018.