The cell membrane: a selective barrier

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   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
   • Chloride ions, because they carry a charge
   • No particle needs one, because the membrane is open

2. 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.

3. 2.

   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
   • Nowhere, because the membrane is a solid wall
   • Between the tails, because small ions slip through
   • Over the top of W, because proteins stay on the surface
4. 3.

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

5. 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.

6. 4.

   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 face the water above; tails face the water below
   • Heads and tails lock together in one solid layer
   • Tails face the water on both sides; heads meet in the middle
7. 5.

   Membrane drawing (model, not to scale). The tails in Milo’s drawing meet in the middle, away from both fluids. Which explanation fits?

   • The tails are water-loving, so they gather in the middle
   • The tails are charged, so ions pull them into the middle
   • The tails are water-fearing, so they pack together away from water
   • The membrane is a solid wall, so the tails are locked in
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 carrier protein, which changes shape to carry glucose
   • A channel protein, which forms an open tunnel for glucose
   • A surface protein, which rests on top of the bilayer
   • 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 phospholipid, which lets sodium ions slip through
    • A carbohydrate chain, which marks the cell’s outside
    • A carrier protein, which changes shape to carry ions
    • A channel protein, which forms a tunnel for ions
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 channel protein, which needs no energy
    • A pump, which uses ATP energy
12. 9.

    Glycoproteins and glycolipids carry sugar chains. In Tala’s drawing, where are such chains found?

    • On the inside surface, facing the cell’s inside
    • On both surfaces of the membrane equally
    • On the outside surface, facing away from the cell
    • In the middle, among the thin tails
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
    • Inside a channel, helping ions cross the bilayer
    • On the outside surface, helping cells recognize each other
    • Alongside the phospholipids, making the membrane a solid wall