3.1.8Movement into and out of Cells
Proteins and Active Transport — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 5 of 5 Unit quiz
Part 1 of 5What Active Transport Is
Some substances must be moved into cells even when there is already more of them inside.
Definition
- Active transport is the movement of particles through a cell membrane from a lower concentration to a higher concentration.
Energy source
- The energy needed comes from respiration, which is why cells that carry out active transport have many mitochondria.
Against the gradient
- Particles move in the opposite direction to the one in which they would naturally diffuse.
Compared with diffusion
- Diffusion is passive and needs no energy because particles move down a concentration gradient.
| Feature | Diffusion | Active transport |
|---|---|---|
| Direction | Down the gradient | Against the gradient |
| Energy from respiration | Not needed | Needed |
| Carrier proteins | Not required | Required |
Part 2 of 5Carrier Proteins at Work (Extended)
Specific carrier proteins embedded in the membrane pick up particular molecules.
1
The substance to be moved combines with a carrier protein molecule in the cell membrane.
2
The carrier uses energy from respiration, which gives it the kinetic energy needed to change shape.
3
The change of shape moves the substance through the membrane against its concentration gradient.
4
The substance is released into the cell and the carrier returns to its original shape ready to be used again.
Part 3 of 5Why Active Transport Matters (Extended)
Why Active Transport Matters (Extended)
Small intestine
- Epithelial cells in the villi take up glucose from digested food even when the concentration in the blood is higher.
Kidney tubules
- Cells in the nephron reabsorb glucose into the blood so that useful sugar is not lost in urine.
Root hair cells
- Plants take up mineral ions from the soil water, where their concentration is often low, using active transport.
Specific carriers
- Each type of carrier protein transports only one kind of substance, so cells can choose what to take in.
Part 4 of 5Rate and Limits
Oxygen supply
- Active transport needs respiration, so a shortage of oxygen slows or stops it.
Temperature
- Warmer conditions can speed respiration and carrier movement, but extreme heat damages proteins.
Number of carriers
- More carrier proteins in a membrane allow more particles to be moved in the same time.
Respiration inhibitors
- Poisons that stop respiration also stop active transport because the energy supply is cut off.
Part 5 of 5Exam Checklist & Tips
3.1.8 – Key Points for the Exam
- Active transport Movement of particles against a concentration gradient using energy from respiration.
- Concentration gradient A difference in concentration between two regions.
- Carrier protein A membrane protein that binds a specific substance and moves it across the membrane.
- Root hair cell A plant cell that takes up water and ions from the soil.
Common Mistakes
- Saying active transport moves particles from high to low concentration; that describes diffusion.
- Forgetting that the energy comes from respiration and writing that carrier proteins make their own energy.
- Using the same carrier for all substances; each carrier protein is specific to one kind of particle.
- Mentioning the phospholipid bilayer in answers; the syllabus only needs carrier proteins and energy.
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