3.3 Active Transport
Movement Against the Concentration Gradient
Core Definition
Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient), using energy from respiration.
Understanding the Energy Requirement
Think of concentration gradients like hills. In diffusion, particles naturally roll downhill from high to low concentration. But in active transport, cells must push particles uphill from low to high concentration, which requires energy.
Interactive Demonstration
Comparison: Diffusion vs Active Transport
Diffusion (Passive)
- • High → Low concentration
- • No energy needed
- • Down gradient (downhill)
- • Natural movement
Active Transport
- • Low → High concentration
- • Requires ATP energy
- • Against gradient (uphill)
- • Forced movement
Key Takeaways
Active transport moves particles from low to high concentration (against the gradient)
Requires energy from respiration (ATP) to work
Protein carriers in the membrane change shape to pump particles across
Essential for ion uptake by root hairs from dilute soil solutions
Without functioning mitochondria (respiration), active transport cannot occur
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