The cell membrane: a selective barrier
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Use the table
Lab card (model data) and drawing, not to scale. A lab-made bilayer had 20 particles of each kind placed on one side. The card gives the count that reached the far side. Version 1: the bilayer alone. Version 2: the bilayer with channel proteins built for sodium ions.
Particle Version 1 (bilayer alone) Version 2 (with sodium channel proteins) oxygen molecules 18 18 carbon dioxide molecules 17 17 sodium ions 1 15 Drawing: letter K points to a channel protein that reaches all the way across the bilayer, with a tunnel shaped to fit sodium ions. The test was read about only: a teacher ran it, and no one handled the lab-made bilayer.
Bo reads a teacher’s lab card and the drawing of protein K. Which conclusion do the card and drawing support?
- The sodium channel proteins also helped oxygen cross the bilayer
- Oxygen crosses the bilayer alone, but sodium ions cross far better through K
- Neither oxygen nor sodium ions can cross without a protein’s help
- Sodium ions slip through the bilayer alone just as easily as oxygen
Use the table
Lab card (model data) and drawing, not to scale. A lab-made bilayer had 20 particles of each kind placed on one side. The card gives the count that reached the far side. Version 1: the bilayer alone. Version 2: the bilayer with protein K and protein L added.
Particle Version 1 (bilayer alone) Version 2 (with K and L) oxygen molecules 18 18 sodium ions 1 15 glucose molecules 1 13 Drawing: letter K points to a protein that reaches all the way across the bilayer with a tunnel shaped to fit sodium ions. Letter L points to a protein that reaches all the way across the bilayer, shaped like a cup that fits glucose and changes shape when it binds one. The test was read about only: a teacher ran it, and no one handled the lab-made bilayer.
Noah uses the card and drawing. Which protein explains why more glucose crossed in version 2, and how does it work?
- L, a carrier that binds glucose and changes shape
- No protein, because glucose slips between the tails over time
- K, a channel that forms an open tunnel for glucose
- L, a surface protein that attracts glucose from above
Use the table
Lab card (model data), not to scale. A lab-made bilayer had 100 water molecules and 100 oxygen molecules placed on one side. The card gives the count that reached the far side after 1 minute. Version 1: the bilayer alone. Version 2: the bilayer with aquaporins added.
Particle Version 1 (bilayer alone) Version 2 (with aquaporins) water molecules 5 80 oxygen molecules 90 90 The test was read about only: a teacher ran it, and no one handled the lab-made bilayer.
Water molecules are small, yet Esme’s lab card shows far more crossed once aquaporins were added. Which explanation fits?
- Aquaporins pushed water across the bilayer by using up some of the cell’s ATP energy
- Aquaporins turned the bilayer into a thinner solid wall for water
- Aquaporins are channel proteins that let water pass at a very high rate
- Water crosses a bilayer freely, so the proteins made no difference
Jun wonders why sodium ions did not cross in version 2, even though channel proteins were added. Which explanation fits?
- Sodium ions cross a plain bilayer alone, so they need no channel
- Channels are specific, so these fit potassium ions and not sodium ions
- The channels stopped working in version 2, so no ions could pass through them
- Proteins rest on the surface, so they cannot help any ion cross
Channel proteins were added, yet Pia’s card shows the carbon dioxide count did not change. Which explanation fits?
- Carbon dioxide has no charge and slips through the lipid middle, so it needs no protein
- Any particle crosses a bilayer freely, so proteins make no difference
- Carbon dioxide is charged, so the new proteins repelled it
- Carbon dioxide crossed through the new proteins in both versions
Use this
Membrane drawing of an animal cell (model, not to scale). A strip of phospholipids with watery fluid outside the cell above and watery fluid inside the cell below. The round heads touch the fluids and the thin tails meet in the middle. Letter K points to a protein that reaches all the way across the strip. Small arrows beside the strip show that the phospholipids and the protein move a little relative to one another.
Kira’s notes say the cell membrane is a solid wall that never changes. Which correction fixes the notes?
- It is a fluid mosaic: its lipids and proteins float and move
- It is a solid wall, but its proteins rest on the surface of the bilayer
- It is fluid, so any molecule passes through it freely
- It is a solid wall, but its tails face the fluid
“model, not to scale” Tala’s notes say sodium ions slip between the tails, so channel protein K is just extra. Which correction fixes the notes?
- Sodium ions need a protein because the membrane is one solid wall around the cell
- Sodium ions need no protein, but glucose molecules do
- Sodium ions are charged and repelled by the tails, so they need a protein
- Sodium ions meet the tails first, because tails face the fluid
Use this
Membrane drawing (model, not to scale). A bilayer of phospholipids with watery fluid outside the cell above and watery fluid inside the cell below. Letter M points to a protein that reaches all the way across the bilayer, with a tunnel shaped to fit chloride ions. Outside the cell: 4 oxygen molecules and 4 chloride ions.
Zee must pick the best claim, with its reason, about oxygen molecules and chloride ions near this bilayer.
- Chloride crosses alone and oxygen needs a protein, because ions are small
- Oxygen crosses alone and chloride needs a protein, because chloride has a charge
- Both cross alone, because the bilayer is open to any particle
- Neither crosses alone, because the cell controls entry with proteins
Ari reads that this animal cell lives in cold conditions. Which claim about cholesterol, with its reason, fits the drawing?
- Cholesterol marks the cell in the cold, because it carries sugar chains
- Cholesterol makes the membrane a solid wall in the cold, because it fills the gaps
- Cholesterol lets ions cross in the cold, because it forms a tunnel
- Cholesterol helps the membrane stay fluid in the cold, because it lies alongside the phospholipids
Ren compares claims about protein K, which lets calcium ions cross. Which claim, with its reason, fits the drawing?
- K is unnecessary, because calcium ions slip between the tails
- K is a peripheral protein, because proteins stay on the surface of the membrane
- K is a piece of a solid wall, because the membrane cannot change
- K is an integral protein, because it spans the bilayer from fluid to fluid