Question 1

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

Accepted Answer

A dynamic structure with proteins embedded in a fluid bilayer of phospholipids.

Question 2

Which property of phospholipids is primarily responsible for the formation of the bilayer in biological membranes?

Accepted Answer

Their amphipathic nature, having both hydrophobic and hydrophilic regions.

Question 3

A researcher observes that a cell membrane becomes more fluid at higher temperatures. Which membrane component is most likely responsible for this change?

Accepted Answer

A higher proportion of unsaturated hydrocarbon tails in phospholipids.

Question 4

Which of the following equations best represents the process of passive diffusion across a membrane?

Accepted Answer

$$ \Delta G = RT \ln \left( \frac{[C]_2}{[C]_1} \right) $$

Question 5

A cell is placed in a solution with a higher concentration of solutes than inside the cell. What will most likely happen to the cell?

Accepted Answer

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

Question 6

Which of the following statements about membrane proteins is correct?

Accepted Answer

Integral proteins span the membrane and are involved in transport and signaling.

Question 7

Cholesterol is an important component of animal cell membranes. What is its primary function?

Accepted Answer

It stabilizes membrane fluidity across temperature changes.

Question 8

Which of the following best explains why ions such as Na	extsuperscript{+} and Cl	extsuperscript{–} cannot easily cross the plasma membrane by simple diffusion?

Accepted Answer

They are charged and cannot pass through the hydrophobic core of the membrane.

Question 9

A scientist tags membrane proteins in a mouse cell and fuses it with a human cell. After several hours, the tagged proteins are found distributed throughout the hybrid cell membrane. What does this experiment demonstrate?

Accepted Answer

Membrane proteins can move laterally within the lipid bilayer.

Question 10

Which process requires energy input from the cell to move substances across the plasma membrane?

Accepted Answer

Active transport

Question 11

Which of the following is a correct description of facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient via transport proteins, without energy input.

Question 12

A cell needs to import large molecules such as proteins. Which process is most likely used?

Accepted Answer

Endocytosis

Question 13

Which of the following factors would most likely decrease membrane fluidity?

Accepted Answer

Increasing the proportion of saturated fatty acids.

Question 14

Which equation best describes the rate of diffusion ($$J) of a $$solute across a membrane?

Accepted Answer

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

Question 15

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

Accepted Answer

Synthesizing phospholipids.

Question 16

A red blood cell is placed in pure water. What will happen to the cell and why?

Accepted Answer

It will burst because water enters the cell by osmosis.

Question 17

Which of the following best explains why the plasma membrane is selectively permeable?

Accepted Answer

It restricts passage based on size, charge, and polarity of molecules.

Question 18

Which of the following would most likely increase the rate of facilitated diffusion?

Accepted Answer

Increasing the number of transport proteins in the membrane.

Question 19

Which of the following is a real-world example of active transport in human physiology?

Accepted Answer

Sodium-potassium pump maintaining ion gradients in nerve cells.

Question 20

Which of the following statements about the movement of phospholipids in the membrane is correct?

Accepted Answer

Phospholipids frequently move laterally within the bilayer.

Structure and Function of Biological Membranes

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