The cell membrane: a selective barrier

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Membrane drawing (model, not to scale). No proteins are drawn. Esme lists three particles near a cell: carbon dioxide, potassium ions and glucose. Which can cross the bilayer on its own, with no protein?

   • No particle can, because gases need a protein too
   • Carbon dioxide, because it has no charge
   • Each of the three, because the bilayer is open
   • Potassium ions, because they are small
2. 2.

   No proteins are drawn. Oxygen, carbon dioxide and chloride ions are outside Bo’s cell. Which one needs a transport protein to cross the bilayer?

   • Oxygen, because gases need a protein to cross
   • Carbon dioxide, because it is the largest of the three
   • No particle needs one, because the membrane is open
   • Chloride ions, because they carry a charge

3. Read this first

   Use this

   Membrane drawing (model, not to scale). A bilayer of phospholipids. Letter W points to a protein that reaches all the way across the bilayer, with a tunnel shaped to fit potassium ions. Outside the cell: 4 potassium ions.

4. 3.

   Potassium ions are outside the cell in Kira’s drawing. Which prediction about how they can cross fits the drawing?

   • Through W, because the tunnel shields them from the tails
   • Over the top of W, because proteins stay on the surface
   • Nowhere, because the membrane is a solid wall
   • Between the tails, because small ions slip through
5. 4.

   Membrane drawing (model, not to scale). Phospholipid heads face the watery fluid on both sides of the membrane. Jun wants to know why. Which explanation fits?

   • The heads are water-fearing, so they stay near the water
   • The heads are water-loving, so they form hydrogen bonds with water
   • The membrane is a solid wall, so heads are pressed outward
   • The tails are water-loving, so they pull the heads outward

6. Use this

   Phospholipids in water (model, not to scale). Each phospholipid has one round head and two thin tails. Water fills the space above and below a double layer of phospholipids.

7. 5.

   Luz reads that phospholipids placed in water form a double layer. Which prediction describes how the two layers line up?

   • Heads face the water on both sides; tails meet in the middle
   • Heads and tails lock together in one solid layer
   • Tails face the water on both sides; heads meet in the middle
   • Heads face the water above; tails face the water below
8. 6.

   Membrane drawing in two steps (model, not to scale). Noah reads about a protein that binds one glucose molecule, changes shape and releases the glucose inside the cell. What kind of protein is it?

   • A surface protein, which rests on top of the bilayer
   • A channel protein, which forms an open tunnel for glucose
   • A carrier protein, which changes shape to carry glucose
   • A phospholipid, which lets sugars slip through the tails

9. Use this

   Membrane drawing (model, not to scale).

10. 7.

    Pia’s drawing shows a protein that reaches across the bilayer and forms a tunnel shaped to fit sodium ions. What kind of protein is it?

    • A carbohydrate chain, which marks the cell’s outside
    • A channel protein, which forms a tunnel for ions
    • A carrier protein, which changes shape to carry ions
    • A phospholipid, which lets sodium ions slip through
11. 8.

    A protein uses ATP energy to move sodium ions out of a cell and potassium ions in. What kind of protein is it, according to Ren’s drawing?

    • A gap in the tails, which lets ions slip across
    • A surface protein, which rests on top of the bilayer
    • A pump, which uses ATP energy
    • A channel protein, which needs no energy
12. 9.

    (model, not to scale). In Zee’s drawing, which protein is a peripheral protein, and why?

    • Neither, because the membrane is a solid wall
    • Both, because membrane proteins stay on the surface
    • N, because it sits on the surface of the membrane
    • M, because it touches both fluids
13. 10.

    Letter K points to cholesterol in Ari’s animal cell drawing. Where does it lie, and what does it do?

    • Alongside the phospholipids, helping keep the membrane fluid
    • On the outside surface, helping cells recognize each other
    • Inside a channel, helping ions cross the bilayer
    • Alongside the phospholipids, making the membrane a solid wall