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 cis-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. Cholesterol ferries ions across the bilayer. True or false?

    Circle one:   True   False

  7. A membrane rich in long saturated tails moves to cold water and its fluidity rises. True or false?

    Circle one:   True   False

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

    • She is right; fluidity and permeability are simply the same single property
    • She mixes them; crossing also needs size, charge and channels
    • She is wrong; no fluid membrane lets anything cross
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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 cis-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. False · Cholesterol tunes movement; it ferries nothing.
  7. False · Cold packs tails tighter so fluidity falls; new kinks can restore it.
  8. She mixes them; crossing also needs size, charge and channels · Shuffling lipids is not the same as crossing the bilayer.
Worksheet · LightMySky