Membrane transport

Membrane transport refers to the process by which molecules and other substances pass through the cell membrane. As cell membranes are semi-permeable, they allow certain molecules to pass through whilst blocking others. This is crucial for the cell’s survival, as it needs to take up nutrients, excrete waste products and regulate its internal environment.

There are various types of membrane transport, including:

1. Passive transport: This is the movement of molecules across the cell membrane that does not require energy (ATP). Passive transport includes diffusion, osmosis and facilitated diffusion.
   • Diffusion is the process by which molecules move from areas of high concentration to areas of low concentration.
   • Osmosis is a specific type of diffusion in which water moves through a semi-permeable membrane.
   • Facilitated diffusion utilises specialised proteins to transport molecules across the cell membrane.
2. Active transport: This process requires energy in the form of ATP to transport molecules against their concentration gradient, i.e. from areas of low concentration to areas of high concentration. Active transport utilises specialised proteins to facilitate this process.
3. Endocytosis and exocytosis: These are processes by which cells take up or release large molecules. In endocytosis, the cell membrane envelops the molecule and forms a vesicle, which enters the cell. In exocytosis, the vesicle containing the molecule leaves the cell.

These various transport methods enable cells to take up nutrients, remove waste products and maintain a constant internal environment, regardless of external conditions.