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?
- Potassium ions, because they are small
- Carbon dioxide, because it has no charge
- Each of the three, because the bilayer is open
- No particle can, because gases need a protein too
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
- No particle needs one, because the membrane is open
- Chloride ions, because they carry a charge
- Carbon dioxide, because it is the largest of the three
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?
- 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
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 and tails lock together in one solid layer
- 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 face the water above; tails face the water below
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 membrane is a solid wall, so the tails are locked in
- The tails are charged, so ions pull them into the middle
- The tails are water-fearing, so they pack together away from water
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 phospholipid, which lets sugars slip through the tails
- A surface protein, which rests on top of the bilayer
- A channel protein, which forms an open tunnel for glucose
Use this
Membrane drawing (model, not to scale).
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
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
(model, not to scale). In Zee’s drawing, which protein is a peripheral protein, and why?
- M, because it touches both fluids
- Neither, because the membrane is a solid wall
- N, because it sits on the surface of the membrane
- Both, because membrane proteins stay on the surface
Letter K points to cholesterol in Ari’s animal cell drawing. Where does it lie, and what does it do?
- Alongside the phospholipids, making the membrane a solid wall
- On the outside surface, helping cells recognize each other
- Alongside the phospholipids, helping keep the membrane fluid
- Inside a channel, helping ions cross the bilayer