Active Transport

This lesson covers active transport as required by the Edexcel GCSE Combined Science specification (1SC0). You need to define active transport, explain why it requires energy, compare it to diffusion and osmosis, and describe key biological examples including root hair cells and the gut lining.

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What Is Active Transport?

Active transport is the movement of substances from a region of lower concentration to a region of higher concentration — against the concentration gradient. This requires energy from cellular respiration.

Key features:

• Moves substances against the concentration gradient (from low to high concentration).
• Requires energy from respiration (ATP).
• Uses specific carrier proteins (transport proteins) in the cell membrane.
• Allows cells to absorb substances even when the concentration inside the cell is already higher than outside.

Exam Tip: The key distinction is the direction of movement. Diffusion and osmosis are passive (high to low concentration). Active transport moves substances from low to high concentration and requires energy.

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Why Is Energy Needed?

In diffusion and osmosis, particles move naturally down their concentration gradient — from high to low concentration. This happens spontaneously and does not require energy.