Question 1

Which of the following best explains why small nonpolar molecules such as $$\mathrm{O_2$}$$ and $$\mathrm{CO_2$}$$ can freely cross the plasma membrane, while ions like $$\mathrm{Na^+}$$ cannot?

Accepted Answer

The nonpolar hydrocarbon tails of phospholipids allow nonpolar molecules to dissolve and pass through, but repel charged ions.

Question 2

A scientist observes that a cell is able to take in large particles from its environment by engulfing them with its plasma membrane. Which process is being described?

Accepted Answer

Endocytosis

Question 3

Which component of the plasma membrane is primarily responsible for maintaining membrane fluidity in animal cells at different temperatures?

Accepted Answer

Cholesterol

Question 4

A red blood cell is placed in a solution containing a high concentration of $$\mathrm{Na^+}$$ ions. Which mechanism will the cell most likely use to maintain its internal ion concentration?

Accepted Answer

Active transport of $$\mathrm{Na^+}$$ out of the cell using the $$\mathrm{Na^+/K^+}$$ pump

Question 5

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

Accepted Answer

A double layer of phospholipids with proteins, cholesterol, glycoproteins, and glycolipids that can move laterally within the membrane

Question 6

Which of the following molecules would most likely require a channel protein to cross the plasma membrane?

Accepted Answer

Sodium ion ($$\mathrm{Na^+})$$

Question 7

A plant cell is placed in pure water. Which structure prevents the cell from bursting due to osmotic pressure?

Accepted Answer

Cell wall

Question 8

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It allows large polar molecules to move down their concentration gradient through transport proteins.

Question 9

A mutation causes a cell to lack aquaporin proteins. Which process would be most directly affected?

Accepted Answer

Rapid movement of water across the membrane

Question 10

Which of the following best explains why the $$\mathrm{Na^+/K^+}$$ pump is essential for nerve cell function?

Accepted Answer

It uses metabolic energy to actively transport $$\mathrm{Na^+}$$ out and $$\mathrm{K^+}$$ into the cell, maintaining the membrane potential.

Question 11

A cell is observed to secrete large quantities of digestive enzymes. Which process is most directly responsible for this secretion?

Accepted Answer

Exocytosis

Question 12

Which of the following scenarios best illustrates selective permeability of the plasma membrane?

Accepted Answer

Small nonpolar molecules pass freely, while ions and large polar molecules require specific transport proteins.

Question 13

A researcher adds a chemical that blocks ATP production in a cell. Which transport process would be most immediately affected?

Accepted Answer

Active transport of $$\mathrm{Na^+}$$ ions

Question 14

Which of the following best describes the orientation of phospholipids in the plasma membrane?

Accepted Answer

Hydrophilic phosphate heads face the aqueous environment, while hydrophobic fatty acid tails face each other in the membrane interior.

Question 15

A bacterial cell is placed in a hypotonic solution. Which structure provides protection against osmotic lysis?

Accepted Answer

Cell wall

Question 16

Which of the following is a key difference between passive and active transport across the plasma membrane?

Accepted Answer

Active transport requires metabolic energy (such as ATP), while passive transport does not.

Question 17

A cell is exposed to a toxin that specifically disrupts the function of membrane proteins with hydrophobic regions. Which process would be most directly impaired?

Accepted Answer

Facilitated diffusion of ions

Question 18

Which of the following best explains why large polar molecules, such as glucose, require facilitated diffusion to enter a cell?

Accepted Answer

Their size and polarity prevent them from passing through the hydrophobic interior of the membrane without a transport protein.

Question 19

A cell is placed in a solution containing a high concentration of $$\mathrm{K^+}$$ ions outside and a low concentration inside. If the cell needs to accumulate more $$\mathrm{K^+}$$, which process will it use?

Accepted Answer

Active transport using the $$\mathrm{Na^+/K^+}$$ pump

Question 20

Which of the following is a direct consequence of the movement of ions across a membrane via active transport?

Accepted Answer

Establishment and maintenance of an electrochemical gradient

Plasma Membrane Structure and Transport Mechanisms

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