Question 1

Which of the following best explains why small, nonpolar molecules such as O$$_2$$ and CO$$_2$$ can easily cross the plasma membrane?

Accepted Answer

They dissolve in the hydrophobic core of the lipid bilayer.

Question 2

A cell is placed in a solution with a higher solute concentration than its cytoplasm. What will happen to the cell due to osmosis?

Accepted Answer

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

Question 3

Which equation correctly describes the rate of diffusion across a membrane?

Accepted Answer

$$F = kA \frac{\Delta c}{d}$$

Question 4

Why do large cells often have internal subdivisions or become long and thin?

Accepted Answer

To increase their surface area to volume ratio and enhance diffusion rates.

Question 5

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It uses channel or carrier proteins to move substances down their electrochemical gradient.

Question 6

What is the main function of aquaporins in the plasma membrane?

Accepted Answer

To allow rapid movement of water molecules across the membrane.

Question 7

A red blood cell is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

The cell will gain water and may burst.

Question 8

Which of the following best describes the sodium-potassium pump (Na$$^+/K$^+-$$ATPase)?

Accepted Answer

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

Question 9

Which of the following is true about the movement of charged particles across membranes?

Accepted Answer

It depends on both the concentration gradient and the electrical gradient (electrochemical gradient).

Question 10

Which of the following best explains why ions such as Na$$^+$$ and Cl$$^-$$ have low permeability across the phospholipid bilayer?

Accepted Answer

Their charge prevents them from passing through the hydrophobic core.

Question 11

Which of the following is an example of secondary active transport?

Accepted Answer

A symporter using the energy from Na$$^+$$ moving down its gradient to transport glucose against its gradient.

Question 12

Which of the following would increase the rate of diffusion across a membrane, according to the equation $$F = kA \frac{\Delta c}{d}$$?

Accepted Answer

Increasing the surface area ($$A).$$

Question 13

Which of the following best describes the difference between channel proteins and carrier proteins?

Accepted Answer

Channel proteins form open pores for specific ions or molecules, while carrier proteins change shape to transport substances.

Question 14

A plant cell's vacuole helps it maintain efficient diffusion by:

Accepted Answer

Reducing the volume of the protoplast, thus decreasing diffusion distance.

Question 15

Which of the following scenarios would result in no net movement of water across a cell membrane?

Accepted Answer

The solution outside the cell is isotonic to the inside.

Question 16

Which of the following is a consequence of a decreased surface area to volume ratio in large cells?

Accepted Answer

Decreased rate of diffusion per unit volume.

Question 17

Which of the following best describes the movement of water during osmosis?

Accepted Answer

Water moves from regions of low solute concentration to regions of high solute concentration.

Question 18

Which of the following is true about the structure of a phospholipid bilayer?

Accepted Answer

Hydrophilic heads face outward, interacting with water.

Question 19

Which of the following is a real-life example of increased surface complexity to enhance diffusion?

Accepted Answer

The presence of microvilli in the small intestine.

Transport of Substances Across Membranes

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