BRAINCAKEPassive and Active Transport
Substances cross cell membranes either by passive transport or by active transport. The difference is where the energy comes from and the direction of movement.
Passive transport does not use energy from ATP. The energy comes from the random kinetic energy of the particles themselves. Substances move down a concentration gradient, from where they are more concentrated to where they are less concentrated, until equilibrium is reached. There are three types:
• diffusion: particles pass through the phospholipid bilayer;
• facilitated diffusion: particles pass through channel or carrier proteins;
• osmosis: the movement of water across a partially permeable membrane.
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Key terms in this lesson
- concentration gradient
- The difference in the concentration of a substance between two regions, which determines the direction of net diffusion.
More in Cell Transport Mechanisms
- The Need for Transport
- Transport Across the Cell Membrane
- Diffusion
- Facilitated Diffusion
- Water Potential ψ
- Osmosis
- Modelling Osmosis
- Osmotic Concentrations
All 18 lessons in Cell Transport Mechanisms · All Edexcel AS-level Biology topics