Q: A sodium-potassium pump moves ions against their concentration gradients. Which equation best represents the stoichiometry of this pump?

$$3 \ \mathrm{Na}^+ \ \text{out}, \ 2 \ \mathrm{K}^+ \ \text{in}$$

Question 1

Which of the following best describes the 'fluid mosaic model' of the plasma membrane?

Accepted Answer

A double layer of phospholipids with proteins and glycoproteins embedded, allowing lateral movement of both lipids and proteins.

Question 2

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

Accepted Answer

Oxygen ($$O_2)$$

Question 3

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

Accepted Answer

The cell will become turgid as water enters by osmosis.

Question 4

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

Accepted Answer

Synthesis of phospholipids

Question 5

Why are some individuals resistant to HIV infection?

Accepted Answer

They lack the CCR5 co-receptor on their cell membranes.

Question 6

Which of the following statements about osmosis is correct?

Accepted Answer

Osmosis is the movement of water from a region of lower solute concentration to a region of higher solute concentration.

Question 7

A sodium-potassium pump moves ions against their concentration gradients. Which equation best represents the stoichiometry of this pump?

Accepted Answer

$$3 \ \mathrm{Na}^+ \ 	ext{out}, \ 2 \ \mathrm{K}^+ \ 	ext{in}$$

Question 8

Which of the following best explains why plant cell membranes remain fluid at lower temperatures?

Accepted Answer

They increase the proportion of unsaturated fatty acids in their membranes.

Question 9

Which process is responsible for the uptake of cholesterol into animal cells?

Accepted Answer

Receptor-mediated endocytosis

Question 10

A cell is placed in a hypertonic solution. What will happen to an animal cell in this environment?

Accepted Answer

It will shrink as water leaves the cell.

Question 11

Which of the following is an example of bulk transport across the plasma membrane?

Accepted Answer

Exocytosis of neurotransmitters

Question 12

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It is a type of passive transport that uses membrane proteins.

Question 13

Which of the following best describes the role of cholesterol in the plasma membrane?

Accepted Answer

It stabilizes membrane fluidity across temperature changes.

Question 14

Which of the following is a correct statement about lipid rafts?

Accepted Answer

They are dynamic microdomains enriched in cholesterol and sphingolipids that organize membrane proteins.

Question 15

A patient with hypercholesterolemia is found to have defective LDL receptors. What is the most direct consequence of this defect?

Accepted Answer

Decreased uptake of cholesterol by cells

Question 16

Which of the following best explains the difference between passive and active transport?

Accepted Answer

Passive transport moves molecules down their concentration gradient without energy input, while active transport requires energy to move molecules against their gradient.

Question 17

Which of the following scenarios would most likely increase the activity of a contractile vacuole in Paramecium?

Accepted Answer

Moving from an isotonic to a hypotonic solution

Question 18

Which of the following best describes the sidedness of membranes in the context of glycoprotein location?

Accepted Answer

Glycoproteins are typically found on the non-cytosolic (extracellular) side of the membrane.

Question 19

Which of the following is a real-world application of understanding membrane protein interactions?

Accepted Answer

Designing drugs that block the interaction between HIV proteins and human receptor proteins.

Question 20

Which of the following best describes the process of exocytosis?

Accepted Answer

The secretion of large molecules when vesicles fuse with the plasma membrane.

Topic3 Cell Membranes: Structure, Function, and Transport Mechanisms

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