The big idea: Many channels in neurons have a gate. What opens the gate differs: a change in voltage, or a neurotransmitter binding.
The points to remember
- Gated channels open and close, so ions can cross only at certain moments.
- Voltage-gated channels open when the voltage across the membrane changes: sodium and potassium channels in neurons.
- Neurotransmitter-gated (ligand-gated) channels open when a chemical binds to them.
- The nicotinic acetylcholine receptor opens when acetylcholine binds, letting Na⁺ in.
- Some channels are mechanically gated: they open when the membrane is stretched or pressed.
- Once open, ions diffuse through, down their gradient: still passive.
Remember it as: Volts or a chemical key: two ways to open a gate.
Real example: nicotine: Nicotine fits the same receptor as acetylcholine and opens it too. That is why these receptors are called nicotinic.
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How it is asked: Paper 1A gives a table of channels and asks how each is gated. Paper 2 asks you to state a type of gated channel other than the one shown.
IB-style questionState[1 mark]
A diagram shows a voltage-gated potassium channel. State another type of gated ion channel.
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See the answer broken into clear points, with guidance on how each point earns marks.