Biology › Section C · Cell structure and membranes › Topic C.8
Active and bulk transport
Diffusion is free, but cells cannot live on downhill flows alone. To hoard potassium, expel sodium, import glucose, or swallow a bacterium whole, a cell must pay - in ATP for pumps, in membrane for bulk cargo. Here is how cells move things the gradient forbids.
In this topic
- Active transport: paying to go uphill
- The electrochemical gradient
- Carrier proteins: uni, sym, and anti
- Worked example: the sodium-potassium pump cycle
- Secondary active transport: spending the battery
- Endocytosis and phagocytosis: swallowing
- Pinocytosis: sipping
- Receptor-mediated endocytosis: targeted uptake
- Exocytosis: exporting in bulk
- Worked example: choosing the transport method
- Common mistakes to avoid
- Key takeaways
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