AP Biology / Unit 2: Cell Structure and Function
2.8 Mechanisms of Transport
Notes
Cells use several mechanisms at once:
- Electrochemical gradients store energy.
- Cotransport: one substance moving down its gradient pulls another against its gradient (e.g., Na⁺-glucose).
- Proton pumps build $\mathrm{H^+}$ gradients used by ATP synthase.
Practice
In Na⁺-glucose cotransport, energy comes from:
Sodium's gradient powers glucose uptake.
If the Na⁺/K⁺ pump stops, cotransport of glucose:
The pump maintains the gradient.
An electrochemical gradient combines:
Both chemical and electrical.
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