Question 1

Which of the following best explains why phospholipids spontaneously form bilayers in aqueous environments?

Accepted Answer

Their hydrophilic heads interact with water, while their hydrophobic tails avoid water and interact with each other.

Question 2

A researcher adds cholesterol to an artificial phospholipid bilayer. What effect will this have on the membrane’s permeability?

Accepted Answer

It will decrease the permeability to most molecules.

Question 3

Which of the following molecules would cross a pure phospholipid bilayer most rapidly?

Accepted Answer

Oxygen ($$\mathrm{O_2$})$$

Question 4

A cell is placed in a hypertonic solution. What will happen to the cell due to osmosis?

Accepted Answer

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

Question 5

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 6

Which structural feature of phospholipids is most responsible for the selective permeability of cell membranes?

Accepted Answer

The amphipathic nature, with hydrophilic heads and hydrophobic tails.

Question 7

A patient with cystic fibrosis has a defective CFTR protein. What is the direct consequence of this defect at the cellular level?

Accepted Answer

Reduced transport of chloride ions ($$\mathrm{Cl^-}) $$across the membrane.

Question 8

Which of the following statements about active transport is correct?

Accepted Answer

It requires carrier proteins that change shape and uses ATP to move substances against their gradient.

Question 9

Which of the following best explains why Gram-positive bacteria stain more intensely than Gram-negative bacteria in the Gram stain test?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer that retains the stain.

Question 10

Which of the following would most likely increase the fluidity of a cell membrane?

Accepted Answer

Increasing the proportion of unsaturated fatty acid tails.

Question 11

A red blood cell is placed in pure water. What process will occur, and what is the likely outcome?

Accepted Answer

Osmosis will cause water to enter the cell, potentially leading to lysis.

Question 12

Which of the following is a function of integral membrane proteins?

Accepted Answer

Forming pores for selective transport of ions and molecules.

Question 13

Which equation best describes the net movement of molecules during diffusion?

Accepted Answer

$$J = -D \frac{dC}{dx}$$

Question 14

Which of the following statements about aquaporins is correct?

Accepted Answer

Aquaporins allow rapid movement of water across membranes but exclude ions and other solutes.

Question 15

Which of the following is NOT a property of channel proteins?

Accepted Answer

They require a change in shape for each molecule transported.

Question 16

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

Accepted Answer

Facilitated diffusion uses membrane proteins to transport molecules that cannot cross the lipid bilayer directly.

Question 17

Which of the following statements about the movement of water across cell membranes is correct?

Accepted Answer

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

Question 18

Which of the following is a major structural difference between Gram-positive and Gram-negative bacteria?

Accepted Answer

Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane.

Question 19

Which of the following would most likely decrease the permeability of a membrane to small molecules?

Accepted Answer

Adding more cholesterol to the membrane.

Question 20

Which of the following best describes the role of peptidoglycan in bacterial cells?

Accepted Answer

It provides structural support and protects against osmotic pressure.

Cell Membranes: Structure, Function, and Transport Mechanisms

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