Cell Membrane
The cell membrane is the partially permeable layer that surrounds every cell and controls the movement of substances into and out of it 1. It is present in plant, animal and bacterial cells alike.
Three Routes Across the Membrane
| Route | Direction of movement | Energy used |
|---|---|---|
| Diffusion | Higher to lower concentration (down the gradient) | None from the cell |
| Osmosis | Water from higher to lower water potential | None from the cell |
| Active transport | Lower to higher concentration (against the gradient) | Released by respiration |
Oxygen and nutrients such as glucose enter cells, while carbon dioxide and other waste products leave. Because the membrane is partially permeable, only certain particles pass through it, and in active transport protein carriers in the membrane move molecules or ions across 1.
Related
- Partially Permeable Membrane - The barrier property that lets only some particles cross.
- Cell - Structural unit bounded by this membrane.
- Cytoplasm - Contents enclosed by the membrane.
- Diffusion - Net particle movement down a concentration gradient.
- Osmosis - Movement of water across this membrane down a water-potential gradient.
- Active Transport - Movement against the gradient through protein carriers.
- Respiration - Supplies the energy for active transport.
- Biology - Cambridge IGCSE life-science area.
Footnotes
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Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 - Cell structure (2.1), diffusion (3.1), osmosis and water potential (3.2), active transport and protein carriers (3.3). ↩ ↩2