Active Transport
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of diffusion and concentration gradients to understand how cells absorb substances against a gradient.
What is diffusion?
The net movement of particles from higher to lower concentration
Does diffusion require energy?
No, it is a passive process
Why might a cell need to move substances against a concentration gradient?
To absorb all available nutrients even if the concentration is higher inside the cell than outside
Topic Explainer Video
Check out this @JoeDoesBiology video that explains different types of cell transport, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Active Transport
What is Active Transport?
- Active transport is the movement of substances against a concentration gradient, from a lower concentration to a higher concentration, using energy from respiration.
Key Features of Active Transport:
|
Feature |
Explanation |
|
Against concentration gradient |
Moves substances from lower to higher concentration. |
|
Requires energy |
Uses energy from respiration in mitochondria. |
|
Requires transport proteins |
Transport proteins called carrier proteins move substances across cell membranes by active transport. |
Where Does Active Transport Happen?
In Plants:
- Root hair cells absorb mineral ions (e.g. nitrates) from the soil, even when their concentration is lower in the soil than in the root cells.
In Animals:
- In the small intestine, glucose and amino acids are absorbed into the blood against their concentration gradient after most has already diffused into the blood.
- This ensures no nutrients are wasted.
Diagram showing glucose being actively transported into a cell, against its concentration gradient.
Factors Affecting the Rate of Active Transport
Active transport is an energy-dependent process, so anything that affects energy supply will influence its rate.
1. Availability of Energy
- Active transport needs energy from aerobic respiration.
- If a cell has more mitochondria, it can respire more, releasing more energy, increasing the rate of active transport.
- Low oxygen levels (e.g. in poorly ventilated soils) reduce respiration and energy release and therefore slow active transport.
2. Temperature
- Higher temperatures increase enzyme and transport protein activity, so transport is faster (up to a point).
- Too high a temperature may denature proteins, stopping active transport.
Key Term
- Active transport – movement against a concentration gradient using energy.
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Exam Tips
- Always say “against a concentration gradient” and “requires energy” for full marks.
- Remeber to link active transport to respiration. Factors that reduce the rate of respiration will also reduce the rate of active transport.
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Practice Question
Describe two ways in which active transport differs from diffusion. (2 marks)
Model Answer:
- Active transport moves substances against their concentration gradient whereas diffusion moves substances down their concentration gradient.
- It requires energy from respiration, whereas diffusion does not (diffusion is passive).
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!