Active transport — AQA GCSE Biology
Test yourself on Active transport with AQA GCSE practice questions.
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Active transport explained
Active transport is the movement of substances across a cell membrane from a region of lower concentration to a region of higher concentration, that is, against a concentration gradient.
Read the full explanation
This is the opposite direction to simple diffusion, which is passive and down a concentration gradient. Because active transport moves substances against the gradient, it requires energy and carrier proteins in the membrane. In plants, root hair cells use active transport to absorb mineral ions such as nitrate from soil, where the soil solution is more dilute than the cell cytoplasm. In animals, cells lining the small intestine use active transport to absorb glucose from the gut when gut concentration is lower than blood concentration. The process is selective because specific carrier proteins transport specific substances.
Your focus
- State the direction of movement in active transport relative to a concentration gradient.
- Explain the role of carrier proteins and energy in active transport.
- Apply the concept to named examples such as mineral ion uptake by root hair cells.
Active transport exam tips
Marking Points
- Define active transport as movement of substances from a more dilute solution to a more concentrated solution, against a concentration gradient.
- Contrast active transport with diffusion, which is passive and moves substances down a concentration gradient.
- State that active transport requires energy from respiration and carrier proteins in the cell membrane.
- Give a named example, such as root hair cells absorbing mineral ions from dilute soil solution.
- Explain that carrier proteins are specific, so active transport allows selective uptake of particular substances.
- Describe how the direction of movement relates to concentration: from lower concentration to higher concentration.
Examiner Tips
- 💡Use the phrase against a concentration gradient when defining active transport, as this distinguishes it from diffusion.
- 💡When giving an example, name the substance and the direction of movement, such as mineral ions entering root hair cells from dilute soil solution.
- 💡If asked to compare transport processes, make clear that active transport requires energy and carrier proteins, whereas diffusion does not.
Common Mistakes
- Saying active transport moves substances from high to low concentration; correct this by stating it moves from more dilute to more concentrated, against the gradient.
- Confusing active transport with osmosis; correct this by noting that osmosis is passive water movement, while active transport uses energy and carrier proteins.
- Forgetting that active transport requires energy; correct this by linking it to respiration and ATP production in the cell.