Here's a breakdown:
* Concentration Gradient: This refers to the difference in concentration of a substance between two areas. Molecules naturally tend to move from an area of high concentration to an area of low concentration.
* Passive Transport: This type of transport doesn't require any energy input from the cell. It relies on the natural movement of molecules down their concentration gradient.
There are four main types of passive transport:
1. Simple Diffusion: This is the movement of molecules directly through the cell membrane, following their concentration gradient. This occurs for small, non-polar molecules like oxygen and carbon dioxide.
2. Facilitated Diffusion: This process uses membrane proteins to help molecules move across the membrane. These proteins can act as channels or carriers to facilitate the movement of specific molecules that would otherwise have difficulty crossing the membrane.
3. Osmosis: This is the movement of water across a semi-permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
4. Filtration: This is the movement of water and small solutes across a membrane from an area of high pressure to an area of low pressure. This is not technically considered diffusion as it is driven by pressure, but it's often grouped with passive transport.
In contrast to passive transport, active transport requires energy to move molecules against their concentration gradient. This means moving molecules from an area of low concentration to an area of high concentration.
