Ion Channels: Selectivity, Gating and the Evidence from Single Channels · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Picky gates that snap open

Science · Organisms & Life Processes · ages 19-20
Name ______________________   Date ____________

  1. Which three cues gate ion channels?

    • Voltage, ligand, and mechanical pull
    • Heat, light, and sound waves
    • Sodium, potassium, and calcium

  2. What decides which ion species a channel passes best?

    • The width of the hole alone
    • The pore-lining amino acids
    • The thickness of the whole membrane

  3. A single ion channel eases part way open like a dimmer switch.

    Circle one:   True   False

  4. A drug makes each sodium channel spend twice as much time open. What happens to the whole-cell current?

    • The whole-cell current grows
    • The whole-cell current reverses direction
    • Each single opening gets smaller

  5. What causes the rising phase of the action potential?

    • Potassium channels open and sodium stays shut
    • The membrane leaks until it runs flat
    • Sodium channels open and sodium rushes in

  6. A touch receptor cell fires when its membrane is pressed. Which gating cue is that?

    • A voltage cue, like a neuron firing
    • A mechanical pull, like a touch receptor
    • A ligand cue, like a muscle at a synapse

  7. A toxin locks voltage-gated sodium channels shut. What happens when the neuron is stimulated past threshold?

    • No spike rises, since no sodium enters
    • A bigger spike rises, since potassium compensates
    • A normal spike rises, since ligands take over

  8. Leo sees a noisy trace hovering between the open and closed levels and says the channel rests half open. What is wrong?

    • The channel is broken and stuck half open
    • Two channels are open at once
    • Fast flickering between open and shut
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Picky gates that snap open W1-mt_2xPzPeXZZ_-s1

  1. Voltage, ligand, and mechanical pull · Those three cues open channels in neurons, synapses, and touch cells.
  2. The pore-lining amino acids · The lining strips water off matching ions and blocks the rest.
  3. False · A single channel flicks between full open and shut, never halfway.
  4. The whole-cell current grows · Total current is channels times single current times open fraction.
  5. Sodium channels open and sodium rushes in · Inflowing sodium shoots the voltage upward past threshold.
  6. A mechanical pull, like a touch receptor · Touch bends the channel protein, which is a mechanical cue.
  7. No spike rises, since no sodium enters · Without inflowing sodium there is no rising phase.
  8. Fast flickering between open and shut · Fast flickering between two levels blurs into noise, but the states stay all or nothing.
Worksheet · LightMySky