Question 1

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

Accepted Answer

Phospholipids are amphipathic, with hydrophilic heads facing water and hydrophobic tails facing inward.

Question 2

A fish species living in cold water is found to have a high proportion of unsaturated fatty acids in its cell membranes. What is the primary advantage of this adaptation?

Accepted Answer

It increases membrane fluidity, preventing solidification at low temperatures.

Question 3

Which statement about membrane proteins is correct?

Accepted Answer

Integral proteins span the membrane and have hydrophobic regions within the core.

Question 4

What effect does cholesterol have on membrane fluidity at warmer temperatures (e.g., 37°C)?

Accepted Answer

Cholesterol restrains phospholipid movement, decreasing fluidity.

Question 5

Which type of molecule can most easily cross the plasma membrane without the aid of transport proteins?

Accepted Answer

Small hydrophobic molecules such as $\mathrm{O_2}$ and $\mathrm{CO_2}$

Question 6

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

Accepted Answer

The cell will gain water and burst (lyse).

Question 7

Which process requires energy input from ATP to move substances against their concentration gradient?

Accepted Answer

Active transport

Question 8

The sodium-potassium pump ($\mathrm{Na^+/K^+}$ pump) moves ions across the plasma membrane. Which of the following correctly describes its action?

Accepted Answer

It moves 3 $\mathrm{Na^+}$ ions out of the cell and 2 $\mathrm{K^+}$ ions in, using ATP.

Question 9

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

Accepted Answer

They facilitate the rapid passive movement of water through the membrane.

Question 10

A plant cell is placed in an isotonic solution. What will happen to the cell?

Accepted Answer

It will become flaccid (limp) due to lack of net water uptake.

Question 11

Which of the following is a function of membrane carbohydrates?

Accepted Answer

They play a key role in cell-to-cell recognition.

Question 12

Which statement about facilitated diffusion is correct?

Accepted Answer

It uses transport proteins to move substances down their concentration gradient.

Question 13

Which type of endocytosis is highly specific and involves receptor proteins?

Accepted Answer

Receptor-mediated endocytosis

Question 14

What is the main difference between channel proteins and carrier proteins in membrane transport?

Accepted Answer

Channel proteins allow passive movement through a tunnel, while carrier proteins undergo conformational changes.

Question 15

Which of the following best describes cotransport in cellular membranes?

Accepted Answer

The downhill diffusion of one solute drives the uphill transport of another.

Question 16

Which process is used by secretory cells, such as pancreatic cells releasing insulin, to export large quantities of macromolecules?

Accepted Answer

Exocytosis

Question 17

Which of the following statements about the fluid mosaic model is true?

Accepted Answer

Proteins and lipids can move laterally within the membrane, contributing to its fluidity.

Question 18

Which of the following would most likely increase the permeability of a cell membrane to water?

Accepted Answer

Increasing the number of aquaporins in the membrane

Question 19

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

Accepted Answer

Catalyzing metabolic reactions in the cytoplasm

Question 20

Which of the following best describes the sidedness (asymmetry) of the plasma membrane?

Accepted Answer

The cytoplasmic and extracellular faces have distinct compositions and distributions of membrane components.

Membrane Transport: Structure and Function of the Plasma Membrane

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