Question 1

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

Accepted Answer

Phospholipids are amphipathic, with hydrophilic heads and hydrophobic tails, causing them to arrange with heads facing water and tails away.

Question 2

A researcher adds cholesterol to a phospholipid bilayer. What is the most likely effect on membrane permeability?

Accepted Answer

Membrane permeability will decrease because cholesterol increases the packing density of the hydrophobic tails.

Question 3

Which of the following molecules would cross a pure phospholipid bilayer most rapidly?

Accepted Answer

Oxygen ($$O_2)$$

Question 4

A cell is placed in a hypertonic solution. What will happen to the cell?

Accepted Answer

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

Question 5

Which statement about the fluid-mosaic model of membrane structure is correct?

Accepted Answer

Some proteins span the membrane, making it a dynamic mosaic of phospholipids and proteins.

Question 6

Which of the following best describes facilitated diffusion?

Accepted Answer

Passive movement of substances across a membrane with the help of transmembrane proteins.

Question 7

What is the primary role of fats (triglycerides) in biological systems?

Accepted Answer

Storing chemical energy due to high-energy bonds in fatty acid chains

Question 8

Which of the following is a consequence of increasing the length of saturated hydrocarbon tails in a phospholipid bilayer?

Accepted Answer

Membrane becomes denser and less permeable due to stronger hydrophobic interactions.

Question 9

A mutation causes the CFTR protein to malfunction in airway cells. What is the physiological consequence?

Accepted Answer

Chloride ions cannot leave the cell, leading to abnormally concentrated secretions.

Question 10

Which equation best represents the net movement of water during osmosis across a selectively permeable membrane?

Accepted Answer

$$\Delta \Psi = \Psi_{inside} - \Psi_{outside}$$, where $$\Psi is $$water potential

Question 11

Which of the following is true about amphipathic proteins in membranes?

Accepted Answer

They can span the membrane, with hydrophobic regions interacting with lipid tails and hydrophilic regions exposed to water.

Question 12

Which process requires an input of energy to move substances across a membrane?

Accepted Answer

Active transport via pumps such as $$Na^+/K^+-$$ATPase

Question 13

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

Accepted Answer

Channel proteins form selective pores for passive diffusion, while carrier proteins undergo conformational changes to move solutes.

Question 14

Which of the following best describes the role of electrochemical gradients in secondary active transport?

Accepted Answer

Electrochemical gradients provide potential energy that powers the movement of another molecule against its gradient.

Question 15

Which of the following statements about the permeability of lipid bilayers is correct?

Accepted Answer

Small nonpolar molecules cross quickly, while large polar or charged molecules cross slowly or not at all.

Question 16

Which of the following is a function of membrane lipids?

Accepted Answer

Store chemical energy, serve as signals, and form waterproof coatings.

Question 17

A cell membrane is composed of phospholipids with short, unsaturated hydrocarbon tails. What property will this membrane most likely exhibit?

Accepted Answer

High permeability to small molecules.

Question 18

Which of the following best describes the process of diffusion?

Accepted Answer

Spontaneous movement of molecules from high to low concentration, increasing entropy.

Question 19

Which of the following is true about the sodium-potassium pump ($$Na^+/K^+-$$ATPase)?

Accepted Answer

It uses ATP to move sodium and potassium ions against their concentration gradients.

Question 20

Which of the following is a likely consequence of decreasing temperature on membrane fluidity and permeability?

Accepted Answer

Membrane fluidity and permeability decrease as temperature drops.

Chapter 6: Lipids, Membranes, and the First Cells – Study Notes

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