Movement Into And Out Of Cells: Active Transport
3.2 Active Transport
Definition
- Movement of molecules/ions across a cell membrane from lower concentration to higher concentration (against the concentration gradient).
- Requires energy from respiration (ATP).
- Uses carrier proteins in the membrane.
Key Features
- Opposite of diffusion and osmosis (goes against gradient).
- Selective process → only certain substances moved.
- Energy-dependent → stops if respiration stops.
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Examples Of Active Transport
- Root hair cells: absorb mineral ions (nitrates, magnesium) from soil even when soil concentration is lower.
- Small intestine villi: absorb glucose and amino acids into blood when their concentration is higher in blood than in lumen.
- Kidneys: reabsorb glucose and ions back into blood from nephron.
Comparison With Other Processes
| Process | Requires Energy? | Movement Direction | Example |
|---|---|---|---|
| Diffusion | No | High → Low | O₂ into blood |
| Osmosis | No | High water potential → Low water potential | Water into root hair cells |
| Active transport | Yes | Low → High | Nitrates into root hair cells |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course