The Fluid Mosaic Model of the Cell Membrane · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The busy border that picks its crossings

Science · Organisms & Life Processes · ages 16-18
Name ______________________   Date ____________

  1. What makes the membrane model fluid?

    • Pieces drift sideways
    • The whole cell swims around
    • Water freezes inside the bilayer

  2. Which way do the phospholipid heads face in the membrane?

    • Toward the water on both sides
    • Toward the tails in the middle
    • All toward the inside of the cell

  3. Ions can slip through the oily middle of the bilayer on their own.

    Circle one:   True   False

  4. What is the difference between a channel and a pump?

    • Channels spend energy while pumps are free
    • Channels let matching ions flow downhill for free while pumps spend energy uphill
    • Pumps only work on oxygen

  5. Why does oxygen cross freely while a sodium ion needs a channel?

    • Oxygen is small and non-polar, while the ion charge cannot dissolve in oil
    • Oxygen is larger than any ion
    • Channels refuse all small molecules

  6. What does cholesterol do when the membrane gets cold?

    • It dissolves all the proteins
    • It bursts out of the sheet
    • It stops the tails packing solid, keeping the sheet flexible

  7. A large polar molecule must enter the cell. Which route should it take?

    • Slip straight between the oily tails
    • Dissolve into the tail core and wait
    • Ride a carrier protein

  8. Receptor proteins ferry cargo by changing shape around it.

    Circle one:   True   False

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Answer key

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

The busy border that picks its crossings W1-mt_-xnAIG5hFc-s1

  1. Pieces drift sideways · Sideways drift of the pieces is the fluid half of the name.
  2. Toward the water on both sides · Heads love water, so they line both faces while tails hide inside.
  3. False · A charge cannot dissolve in oil, so ions need protein doors.
  4. Channels let matching ions flow downhill for free while pumps spend energy uphill · Downhill trips are free and uphill trips must be paid for.
  5. Oxygen is small and non-polar, while the ion charge cannot dissolve in oil · Oil welcomes tiny non-polar travellers and bars charged ones.
  6. It stops the tails packing solid, keeping the sheet flexible · Wedged cholesterol blocks packing, so the sheet stays runny enough to work.
  7. Ride a carrier protein · Bulky polar cargo cannot pass alone, so it needs a ferried protein route.
  8. False · Carriers ferry by changing shape, while receptors catch signals from outside.
Worksheet · LightMySky