Identify protein carriers in active transport
Link membrane carrier proteins with energy-dependent transfer of molecules or ions.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall the active-transport definition and membrane function.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What type of structure carries particles during active transport?
What you will learn
- Link membrane carrier proteins with energy-dependent transfer of molecules or ions.
- Apply the idea to a supplied biological example or investigation.
The membrane contains transport proteins
Protein carriers move molecules or ions across a membrane during active transport. In a schematic model, the transported particle interacts with a membrane carrier, and an energy-dependent change enables transfer across the membrane. The carrier is a protein structure, not a pore in the cellulose wall.
Energy from respiration is required for active transport against the gradient. The carrier does not create energy or turn the transported ion into water. An icon is a simplified representation rather than a complete molecular mechanism or measured protein shape.
Do not overgeneralise the protein clue
A protein-assisted transfer is not automatically active transport: some membrane proteins also help passive transfer. To classify the supplied active model, use the against-gradient direction and respiratory energy requirement as well as the carrier.
Different molecules and ions can have different transport routes. A named carrier in a question supports that stated transfer; it does not prove every possible solute uses the same carrier or crosses at the same rate.
Pause and explain
Why is seeing a transport protein alone insufficient to identify active transport?
Worked example
A membrane protein transfers an ion from 3 units to 10 units using respiratory energy. Explain the protein role.
Show the worked solution
- The protein is a carrier spanning the membrane.
- It enables transfer of the ion.
- Against-gradient transfer requires the supplied energy.
Answer A protein carrier mediates active ion transfer across the membrane.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name the membrane structure used in the active-transport model.
Give me a hint
It is a protein.
Compare my reasoning
- Carrier proteins move the named particle across.
Protein carrier.
Look for these in your work
- Do not name a cellulose wall.
State two other features needed to identify active transfer, besides a carrier.
Give me a hint
Use direction and energy.
Compare my reasoning
- Movement is against the particle concentration gradient.
- Energy comes from respiration.
Against-gradient movement and respiratory energy.
Look for these in your work
- Give both.
A protein helps a solute move from high to low concentration without respiratory energy supply. Is that fact alone proof of active transport?
Give me a hint
Keep the classification criteria together.
Compare my reasoning
- Direction is down the gradient.
- The active energy condition is absent.
No; a protein-assisted passive transfer is possible.
Look for these in your work
- Do not classify all proteins as active pumps.
Common mistakes
- A carrier alone does not prove active transport.
- The protein is part of the membrane, not the supporting wall.
What can you explain now?
Why is seeing a transport protein alone insufficient to identify active transport?
Compare with the explanation
Some protein-assisted transfers are passive.
Gradient direction and energy must also be considered.
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Make it stick
Link carrier, named substance, gradient and respiratory energy.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.