Question 1

Which of the following best explains why living cells must expend energy to maintain chemical gradients across their plasma membranes?

Accepted Answer

Gradients are unstable and will dissipate unless energy is used to maintain them against equilibrium.

Question 2

A cell is placed in a solution where the concentration of solute outside the cell is higher than inside. Which process will most likely occur if the membrane is permeable to water but not to the solute?

Accepted Answer

Water will move out of the cell by osmosis, causing the cell to shrink.

Question 3

Which equation correctly represents the relationship between diffusion rate ($$J$$), surface area ($$A$$), concentration gradient ($$\Delta C$$), and membrane thickness ($$d$$)?

Accepted Answer

$$J = \frac{A \cdot \Delta C}{d}$$

Question 4

A scientist observes that after a period of time, the concentration of a dye is equal on both sides of a membrane. What has been reached?

Accepted Answer

Dynamic equilibrium

Question 5

Which of the following molecules is LEAST likely to diffuse directly through the phospholipid bilayer of a plasma membrane?

Accepted Answer

Sodium ion ($$Na^+)$$

Question 6

A red blood cell is placed in pure water. Which of the following best describes what happens and why?

Accepted Answer

Water moves into the cell by osmosis, causing it to swell and possibly burst.

Question 7

Which of the following best describes facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient through a membrane protein, without energy input.

Question 8

A neuron uses the sodium-potassium pump to maintain a high concentration of $$K^+$$ inside and $$Na^+$$ outside the cell. Which type of transport is this and what is the energy source?

Accepted Answer

Active transport; energy from ATP hydrolysis

Question 9

Which of the following statements about the fluid mosaic model of the plasma membrane is correct?

Accepted Answer

Proteins and lipids can move laterally within the layer, contributing to membrane fluidity.

Question 10

Which of the following best explains why cholesterol is important in animal cell membranes?

Accepted Answer

It stabilizes membrane fluidity across temperature changes.

Question 11

A cell is placed in a solution and water moves into the cell. Which term best describes the solution relative to the cell?

Accepted Answer

Hypotonic

Question 12

Which of the following is a function of membrane carbohydrates?

Accepted Answer

Acting as markers for cell recognition

Question 13

Which of the following best describes the role of channel proteins in the plasma membrane?

Accepted Answer

They allow specific molecules to cross the membrane by providing a hydrophilic passageway.

Question 14

Which of the following scenarios best illustrates the concept of dynamic equilibrium in diffusion?

Accepted Answer

Particles continue to move randomly, but there is no net change in concentration across the membrane.

Question 15

Which of the following is true about the movement of ions across a semipermeable membrane?

Accepted Answer

Ions require specific transport proteins to cross the membrane.

Question 16

A cell expends energy to move glucose into the cell against its concentration gradient. Which equation best represents the change in free energy ($$\Delta G) $$for this process?

Accepted Answer

$$\Delta G \u003e 0$$

Question 17

Which of the following best describes the difference between simple diffusion and facilitated diffusion?

Accepted Answer

Facilitated diffusion requires membrane proteins, while simple diffusion does not.

Question 18

Which of the following would most likely increase the rate of diffusion of a substance across a membrane?

Accepted Answer

Increasing the surface area of the membrane

Question 19

A mutation causes a cell to produce saturated fatty acids instead of unsaturated fatty acids in its membrane lipids. What is the most likely effect on the cell membrane at low temperatures?

Accepted Answer

The membrane will become less fluid and may solidify.

Question 20

Which of the following best explains why the maintenance of chemical gradients is essential for life?

Accepted Answer

Gradients allow cells to perform work, such as ATP synthesis and nerve impulse transmission.

Gradients, Equilibrium, and Membrane Transport in Cells

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