1. The table below shows the chemical characteristics of four substances.

Based on the data, which substance will diffuse through a cell membrane most easily?

(A) Substance 1

Distractor Rationale:

This answer suggests the student may understand that small size is important for diffusion

through membranes, but does not understand that charged ions do not easily pass

through membrane lipids because the phospholipid bilayer is hydrophobic.

(B) Substance 2

Distractor Rationale:

This answer suggests the student may understand that small size is important for diffusion

through membranes, but does not understand that although cell membranes have both

polar and non-polar properties, polar molecules do not easily pass through the non-polar

lipid region of the membrane.

(C) Substance 3

Rationale:

This answer suggests the student understands that small size is an important characteristic

that allows substances to diffuse through plasma membranes, and that the molecule’s non-

polarity is an important characteristic because of the non-polarity of the lipid tails of

phospholipids.

(D) Substance 4

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Distractor Rationale:

This answer suggests the student may understand that non-polarity is an important

characteristic for being able to diffuse through membranes, but does not understand that

large molecules do not easily pass through the lipid region of the membrane due to their

size.

Aligned to: LO 2.9 CA 2.9: Represent & Model Matter Exchange

2. In a person with cystic fibrosis, epithelial cells lining the lungs and digestive system lack a

membrane protein needed to remove excess chloride ions from the cell. Which statement best

explains how this disorder affects an epithelial cell?

(A) The low concentration of chloride ions inside the cell causes water to move from the cell to

the cytoplasm, resulting in the cell becoming dehydrated.

Distractor Rationale:

This answer suggests the student may understand that a low concentration of chloride ions

inside the cell would cause water to move out of the cell, but does not understand that the

ion concentration inside the cell is high, and that water will flow into the cell and cause it to

swell and possibly burst.

(B) The high concentration of chloride ions inside the cell causes sodium ions to diffuse into the

cell, resulting in the formation of sodium chloride crystals.

Distractor Rationale:

This answer suggests the student may understand that substances can diffuse across the

plasma membrane and that the chloride ion concentration inside the cell is high, but does

not understand that sodium ions do not move across the plasma membrane through simple

diffusion, and that water would move into the cell and cause the cell to swell.

(C) The low concentration of chloride ions inside the cell causes sodium ions to diffuse into the

cell, resulting in shrinking and shriveling of the cell.

Distractor Rationale:

This answer suggests the student may understand that a low concentration of chloride ions

inside the cell relative to the concentration outside the cell will cause the cell to shrink and

shrivel, but does not understand that only water moves into and out of the cell, that the

concentration of chloride ions is higher inside the cell relative to outside, and that the higher

ion concentration causes water to move into the cell and causes the cell to swell.

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(D) The high concentration of chloride ions inside the cell causes water to diffuse into the cell,

resulting in swelling and bursting of the cell.

Rationale:

This answer suggests the student understands that a high chloride concentration inside the

cell causes water to diffuse across the plasma membrane into the cell, which causes the cell

to swell.

Aligned to: LO 2.9 CA 2.9: Represent & Model Matter Exchange

3. The diagram below shows the movement of particles across a cell membrane.

Which statement describes the process most likely represented by the diagram?

(A) Oxygen is moving into a cell via simple diffusion.

Rationale:

This answer suggests the student understands that oxygen can pass through the cell

membrane by simple diffusion because oxygen is a small, nonpolar molecule.

(B) Sodium ions are moving into a cell via osmosis.

Distractor Rationale:

This answer suggests the student may understand that water moves across a cell

membrane via osmosis, but does not understand that osmosis involves only the movement

of water molecules, and not ions.

(C) Glucose is being moved into a cell via active transport.

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Distractor Rationale:

This answer suggests the student may understand that glucose can move across a cell

membrane via active transport, but does not understand that carrier proteins are involved

and that the movement is usually against a concentration gradient.

(D) Proteins are being moved into a cell via endocytosis.

Distractor Rationale:

This answer suggests the student understands that proteins could move across a cell

membrane via endocytosis, but does not understand that endocytosis involves the

membrane wrapping around the molecule.

Aligned to: LO 2.9 CA 2.9: Represent & Model Matter Exchange

4. The diagram below shows the movement of ions through the phospholipid bilayer of a cell.

Based on the diagram, which statement best explains the movement of the ions through the

phospholipid bilayer?

(A) The ions can diffuse across the phospholipid bilayer because the ions are moving against

the osmotic potential.

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Distractor Rationale:

This answer suggests the student may understand that diffusion is the movement of ions

from high concentration to low concentration, but does not understand that osmotic

potential refers to the movement of water and not the movement of ions.

(B) The ions are transported across the phospholipid bilayer because the ions are moving

against the concentration gradient.

Distractor Rationale:

This answer suggests the student may understand that the ions must be transported across

the phospholipid bilayer, but does not understand that the ions must be transported

because they are charged, and that the ions are not moving against a concentration

gradient.

(C) The ions can diffuse across the phospholipid bilayer because the ions are nonpolar.

Distractor Rationale:

This answer suggests the student may understand that diffusion is the movement of a

substance from high concentration to low concentration, but does not understand that an

ion is charged and requires a channel protein to move across the phospholipid bilayer.

(D) The ions are transported across the phospholipid bilayer because the ions are charged.

Rationale:

This answer suggests the student understands that the ions are moving from an area of

high concentration to an area of low concentration via facilitated diffusion through a protein

channel because they are charged.

Aligned to: LO 2.9 CA 2.9: Represent & Model Matter Exchange

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