Question 1

Which of the following best describes the amphipathic nature of phospholipids in the plasma membrane?

Accepted Answer

They have hydrophilic heads and hydrophobic tails, allowing them to form a bilayer with heads facing water and tails shielded from water.

Question 2

A researcher observes that a cell membrane becomes more rigid at lower temperatures. Which membrane component is most likely to help maintain membrane fluidity under these conditions?

Accepted Answer

Cholesterol, because it disrupts the regular packing of phospholipids at low temperatures.

Question 3

Which of the following statements about membrane proteins is correct?

Accepted Answer

Integral proteins typically span the membrane and have hydrophobic regions that interact with the lipid bilayer.

Question 4

A patient with a genetic mutation lacks functional CCR5 receptors on their cell membranes. What is the most likely consequence of this mutation?

Accepted Answer

The patient is resistant to HIV infection because HIV cannot enter cells without CCR5.

Question 5

Which of the following best explains why O$$_2$$ and CO$$_2$$ can diffuse directly across the plasma membrane without the need for transport proteins?

Accepted Answer

They are small, nonpolar molecules that can dissolve in the hydrophobic core of the lipid bilayer.

Question 6

Refer to the diagram showing water movement across a membrane (Image 3). What is the main reason for the net movement of water molecules from left to right?

Accepted Answer

There are more free water molecules (higher water potential) on the left, so water moves toward the side with lower water potential (right).

Question 7

Which of the following best describes the function of aquaporins in the plasma membrane?

Accepted Answer

They facilitate the rapid diffusion of water molecules across the membrane.

Question 8

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

Accepted Answer

It will lose water and shrink because the solution is hypertonic.

Question 9

Which process is responsible for the uptake of bulk quantities of specific molecules, such as cholesterol, into animal cells?

Accepted Answer

Receptor-mediated endocytosis

Question 10

A plant cell is placed in a hypotonic solution. What is the expected outcome, and why?

Accepted Answer

The cell will become turgid as water enters, but the cell wall prevents bursting.

Question 11

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

Accepted Answer

It uses ATP to move 3 Na$$^+$$ ions out and 2 K$$^+$$ ions into the cell, maintaining concentration gradients.

Question 12

Which of the following is true regarding the electrochemical gradient?

Accepted Answer

It is determined by both the concentration gradient and the membrane potential.

Question 13

A solution has a high osmolarity. What can you infer about its water potential and the direction water will move if a cell is placed in this solution?

Accepted Answer

It has low water potential, so water will move out of the cell into the solution.

Question 14

Refer to the water potential graph (Image 2). Over time, what is the most likely explanation for the convergence of cell and environment water potentials?

Accepted Answer

Water moves from higher to lower water potential until equilibrium is reached.

Question 15

Which of the following best describes cotransport in plant cells?

Accepted Answer

A proton gradient established by ATP-powered pumps drives the active transport of sucrose into the cell.

Question 16

Which of the following is NOT a function of membrane proteins?

Accepted Answer

Synthesis of DNA

Question 17

During exocytosis, what happens to the vesicle membrane?

Accepted Answer

It becomes part of the plasma membrane.

Question 18

Which of the following best explains why facilitated diffusion does not require energy?

Accepted Answer

Molecules move down their concentration gradient with the help of transport proteins.

Question 19

Which of the following is a real-world example of receptor-mediated endocytosis?

Accepted Answer

Human cells taking in cholesterol via LDL receptors.

Membrane Structure and Function: Fluidity, Permeability, and Transport

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