Practice question · Select all that apply
Which forms of transport require the cell to spend energy?
Hints
- Energy is needed only to move something against its gradient, or to move bulk material.
- Anything travelling down its own gradient is free.
Show the answer
- A. Endocytosis engulfing a large particle
- C. The sodium-potassium pump moving ions against their gradient
Why
Pumping against a gradient and bulk transport both cost ATP. Oxygen diffusion and facilitated glucose transport both run down a gradient and are free, facilitated diffusion uses a protein but no energy, which is the distinction that catches people out.
Practise Membranes, Transport and the Energy Currency
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