AP Biology: Cell Membrane Practice Questions

Practice Test

Name: ______________________ Date: __________

Choose the best answer for each question.

1. The fluid mosaic model describes the cell membrane as:
1. A) A rigid lattice of proteins
2. B) A flexible bilayer of phospholipids with embedded proteins
3. C) A single layer of lipids
4. D) A protein sheet bonded to glucose
2. Which of the following moves freely across a phospholipid bilayer without a protein channel?
1. A) Sodium ions
2. B) Glucose
3. C) Water (slowly)
4. D) Large polar molecules
3. Active transport differs from facilitated diffusion because it:
1. A) Requires ATP and can move solutes against their gradient
2. B) Uses no proteins
3. C) Only moves water
4. D) Always moves solutes down their gradient
4. A red blood cell placed in a hypertonic solution will:
1. A) Swell and lyse
2. B) Stay the same
3. C) Shrink (crenate)
4. D) Divide rapidly
5. Cholesterol in animal cell membranes:
1. A) Increases membrane permeability to all solutes
2. B) Modulates fluidity over a range of temperatures
3. C) Replaces phospholipids
4. D) Only appears in plant cells

Answer Key

1. BPhospholipid bilayer with proteins that move laterally — Singer and Nicolson, 1972.
2. CSmall uncharged molecules like O2, CO2, and slowly water can diffuse directly. Aquaporins speed water transport.
3. AActive transport pumps solutes against the gradient using ATP. Facilitated diffusion is passive.
4. CWater moves out of the cell toward the higher solute concentration, causing it to shrink.
5. BCholesterol stabilizes the membrane: it limits fluidity at high temperatures and prevents stiffening at low ones.