The cell membrane: a selective barrier
Grade 9 Science Worksheet
Circle the best answer.
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?
- Nowhere, because the membrane is a solid wall
- Over the top of W, because proteins stay on the surface
- Between the tails, because small ions slip through
- Through W, because the tunnel shields them from the tails
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 tails are water-loving, so they pull the heads outward
- The heads are water-loving, so they form hydrogen bonds with water
- The membrane is a solid wall, so heads are pressed outward
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 face the water above; tails face the water below
- Heads and tails lock together in one solid layer
Membrane drawing (model, not to scale). The tails in Milo’s drawing meet in the middle, away from both fluids. Which explanation fits?
- The membrane is a solid wall, so the tails are locked in
- The tails are water-fearing, so they pack together away from water
- The tails are water-loving, so they gather in the middle
- The tails are charged, so ions pull them into the middle
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 phospholipid, which lets sugars slip through the tails
- A surface protein, which rests on top of the bilayer
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 phospholipid, which lets sodium ions slip through
- A channel protein, which forms a tunnel for ions
- A carrier protein, which changes shape to carry ions
- A carbohydrate chain, which marks the cell’s outside
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 surface protein, which rests on top of the bilayer
- A gap in the tails, which lets ions slip across
- A pump, which uses ATP energy
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
- In the middle, among the thin tails
- On the outside surface, facing away from the cell
(model, not to scale). In Zee’s drawing, which protein is a peripheral protein, and why?
- N, because it sits on the surface of the membrane
- M, because it touches both fluids
- Both, because membrane proteins stay on the surface
- Neither, because the membrane is a solid wall
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
- 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