IB Biology HL 2.1.14 Gated Ion Channels in Neurons Question Bank

Practise IB Biology HL 2.1.14 through exact HL questions on ligand- and voltage-gated channels, potassium movement and neuronal membrane-potential changes.

Exam points

Distinguish ligand-gated and voltage-gated channels by the stimulus that opens each channel.
Explain how selective potassium movement through a voltage-gated channel changes membrane potential.
Use a nerve-impulse sequence to identify channel state, ion direction and timing.

[Maximum number: 4]

Voltage-gated ion channels are proteins that are embedded in the phospholipid bilayer of plasma membranes. They conduct ions at high rates, regulated by the voltage across the membrane. The diagram shows a typical voltage-gated potassium ( $\mathrm{K}^{+}$ ) channel when it is closed and when it is open.

Figure for Question B2.1.14 (HL)—Gated ion channels in neurons question 1 — IB Biology HL

(a)

Explain the action of the voltage-gated potassium channel during a nerve impulse.

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a. (voltage-gated) potassium channels are closed when there is a negative membrane potential / when there are (relatively) more negative charges inside / (relatively) more positive charges outside;

b. (voltage-gated) potassium channels open after depolarization of the axon / after closing of sodium channels / when a positive membrane potential develops / at +30 mV / at +40 mV ;

c. $\mathrm{K}^{+}$ ions diffuse out of the cell / efflux of $\mathrm{K}^{+}$ ;

d. (efflux of $\mathrm{K}^{+}$ ) causes/results in/happens during repolarization / membrane potential returns to -70 mV / to the resting potential;

e. (voltage-gated) potassium channels close again (to terminate the action potential) OR

globular protein ball (attached by a flexible chain of amino acids) blocks/closes the channel;

f. (following an action potential) hyperpolarization can occur (due to slow closing of potassium channels / continued efflux of $\mathrm{K}^{+}$ before potassium channels close / nature of potassium channels);

3

Marking guidance:

max

(b)

State another type of gated ion channel.

[ 1 ]

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B2.1.14 (HL)—Gated ion channels in neurons question 1

Question (a)

Question (b)