Membrane Lipid Composition, Asymmetry and Fluidity · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Two faces, one fluid sheet

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

  1. The two leaflets of a cell membrane carry identical lipids.

    Circle one:   True   False

  2. Which fatty acid tails make a membrane more fluid?

    • Long saturated tails that pack tight
    • Extra cholesterol packed between every lipid
    • Kinked unsaturated tails that push apart

  3. What keeps the two leaflets different from each other?

    • Enzymes that spend energy
    • Cholesterol that glues both faces together
    • Proteins that stop all lipid movement

  4. How does leaflet asymmetry mark a dying cell?

    • It pumps extra cholesterol into the blood
    • It seals its channels to trap nutrients
    • Inner lipid flips out as eat-me flag

  5. A pond cools in autumn and a cell's membrane stiffens. How can the cell remodel its lipids to stay fluid?

    • Lengthen every tail to pack tighter
    • Add unsaturated tails to loosen packing
    • Remove all cholesterol to freeze the bilayer

  6. What does cholesterol do in the membrane?

    • Tunes how freely lipids move
    • Cholesterol ferries ions across the bilayer
    • Cholesterol builds the phosphate heads

  7. A membrane rich in long saturated tails moves from warm to cold water. What happens, and how could the cell fix it?

    • Fluidity rises and nothing needs fixing
    • Permeability rises and channels close
    • Fluidity falls; kinks can restore it

  8. Mia says a very fluid membrane is automatically very permeable to everything. What is wrong?

    • She is right; fluidity and permeability are the same property
    • She mixes two properties; permeability also needs size, charge, and channels
    • She is wrong; fluid membranes block everything
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Answer key

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

Two faces, one fluid sheet W1-mt_PIk59MG-gN-s1

  1. False · The two leaflets carry different lipids, kept different with energy.
  2. Kinked unsaturated tails that push apart · Kinks stop tight packing, so the bilayer stays fluid.
  3. Enzymes that spend energy · Asymmetry is maintained work, not a passive accident.
  4. Inner lipid flips out as eat-me flag · The flipped lipid marks the cell for cleanup.
  5. Add unsaturated tails to loosen packing · Unsaturated kinks restore shuffling as the cold stiffens the membrane.
  6. Tunes how freely lipids move · Cholesterol sets fluidity, not transport or head structure.
  7. Fluidity falls; kinks can restore it · Cold packs tails tighter; kinks reopen the packing.
  8. She mixes two properties; permeability also needs size, charge, and channels · Shuffling lipids is not the same as crossing the bilayer.
Worksheet · LightMySky