The cell membrane: a selective barrier
Grade 9 Science Worksheet
Circle the best answer.
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?
- Carbon dioxide, because it has no charge
- No particle can, because gases need a protein too
- Potassium ions, because they are small
- Each of the three, because the bilayer is open
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
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.
Potassium ions are outside the cell in Kira’s drawing. Which prediction about how they can cross fits the drawing?
- Between the tails, because small ions slip through
- 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
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 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-fearing, so they stay near the water
- The heads are water-loving, so they form hydrogen bonds with water
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.
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
- Tails face the water on both sides; heads meet in the middle
- Heads and tails lock together in one solid layer
- Heads face the water above; tails face the water below
Use this
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-fearing, so they pack together away from water
- The tails are charged, so ions pull them into the middle
- The membrane is a solid wall, so the tails are locked in
- The tails are water-loving, so they gather in the middle
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 channel protein, which forms a tunnel for ions
- A carbohydrate chain, which marks the cell’s outside
- A carrier protein, which changes shape to carry ions
- A phospholipid, which lets sodium ions slip through
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 channel protein, which needs no energy
- A pump, which uses ATP energy
- A surface protein, which rests on top of the bilayer
- A gap in the tails, which lets ions slip across
Glycoproteins and glycolipids carry sugar chains. In Tala’s drawing, where are such chains found?
- On both surfaces of the membrane equally
- On the inside surface, facing the cell’s inside
- On the outside surface, facing away from the cell
- In the middle, among the thin tails
(model, not to scale). In Zee’s drawing, which protein is a peripheral protein, and why?
- Both, because membrane proteins stay on the surface
- M, because it touches both fluids
- N, because it sits on the surface of the membrane
- Neither, because the membrane is a solid wall