Question 1

Which of the following best describes the fluid-mosaic model of biological membranes?

Accepted Answer

A double layer of phospholipids with proteins embedded throughout, where both lipids and proteins can move laterally within the layer.

Question 2

A red blood cell is placed in a solution and begins to swell and eventually bursts. Which term best describes the tonicity of the solution relative to the cell, and what is the direction of water movement?

Accepted Answer

The solution is hypotonic; water moves into the cell.

Question 3

Which of the following molecules would most easily diffuse directly through a pure phospholipid bilayer without the aid of a transport protein?

Accepted Answer

Oxygen ($O_2$)

Question 4

A plant cell is placed in a solution with a higher solute concentration than its cytoplasm. What will happen to the cell, and what is the term for this process?

Accepted Answer

The cell will lose water and the plasma membrane will pull away from the cell wall; this is called plasmolysis.

Question 5

Which of the following best explains why cholesterol is important for membrane fluidity in animal cells?

Accepted Answer

Cholesterol maintains membrane fluidity by restraining phospholipid movement at high temperatures and preventing tight packing at low temperatures.

Question 6

Which of the following is an example of active transport across a cell membrane?

Accepted Answer

Movement of $Na^+$ ions from low to high concentration using the sodium-potassium pump, requiring ATP.

Question 7

A cell uses a proton pump to create a high concentration of $H^+$ ions outside the membrane. This gradient is then used to transport sucrose into the cell against its concentration gradient. What is this type of transport called?

Accepted Answer

Cotransport (secondary active transport)

Question 8

Which of the following best describes the process of osmosis?

Accepted Answer

The movement of water molecules from an area of low solute concentration to high solute concentration through a selectively permeable membrane.

Question 9

A patient is given an intravenous (IV) solution that is hypertonic relative to their blood plasma. What is the most likely effect on their red blood cells?

Accepted Answer

The cells will shrink as water leaves the cells.

Question 10

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It uses transport proteins to move substances down their concentration gradient.

Question 11

A cell engulfs a large particle by wrapping its plasma membrane around it and forming a vesicle. What is this process called?

Accepted Answer

Phagocytosis

Question 12

Which of the following best explains why hydrophobic molecules can cross the plasma membrane more easily than hydrophilic molecules?

Accepted Answer

Hydrophobic molecules dissolve in the hydrophobic core of the phospholipid bilayer.

Question 13

Which equation correctly represents the calculation of osmotic pressure ($\Pi$) using van 't Hoff's law?

Accepted Answer

$\Pi = iMRT$

Question 14

A mutation causes a cell to lack functional aquaporins. Which process would be most directly affected?

Accepted Answer

Osmosis of water across the membrane

Question 15

Which of the following is NOT a component of the endomembrane system in eukaryotic cells?

Accepted Answer

Mitochondria

Question 16

A cell is placed in an isotonic solution. What will happen to the cell's volume over time?

Accepted Answer

The cell's volume will remain constant as there is no net movement of water.

Question 17

Which of the following best describes the role of the sodium-potassium pump in animal cells?

Accepted Answer

It uses ATP to move $Na^+$ out of the cell and $K^+$ into the cell, both against their concentration gradients.

Question 18

Which of the following scenarios best illustrates the concept of selective permeability of the plasma membrane?

Accepted Answer

Glucose requires a specific transport protein to enter the cell, while $O_2$ diffuses directly through the membrane.

Question 19

A patient with acid reflux is prescribed a proton pump inhibitor. What is the direct effect of this medication at the cellular level?

Accepted Answer

It blocks the active transport of $H^+$ ions into the stomach, reducing acid secretion.

Question 20

Which of the following best explains why cells with a higher surface-area-to-volume (SAV) ratio are more efficient at exchanging materials with their environment?

Accepted Answer

A higher SAV ratio increases the rate at which materials can diffuse across the membrane relative to the cell's volume.

Membrane Structure and Transport in Cells

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