Question 1

Which statement best describes the fluid mosaic model of biological membranes?

Accepted Answer

Membranes are composed of a phospholipid bilayer with proteins and other molecules embedded and moving laterally, creating a dynamic and flexible structure.

Question 2

Which property of phospholipids is most responsible for the formation of bilayers in aqueous environments?

Accepted Answer

Their amphipathic nature, having both hydrophilic and hydrophobic regions.

Question 3

A scientist observes that a cell membrane remains fluid at lower temperatures. Which membrane component is most likely present in higher amounts to account for this observation?

Accepted Answer

Cholesterol

Question 4

Which of the following best explains why cell membranes are selectively permeable?

Accepted Answer

The amphipathic nature of phospholipids and the specific transport proteins embedded in the membrane.

Question 5

A red blood cell placed in a hypotonic solution will:

Accepted Answer

Swell and potentially burst as water enters the cell by osmosis.

Question 6

Which equation correctly represents the relationship for diffusion rate ($J$) across a membrane, given the concentration gradient ($\Delta C$) and membrane permeability ($P$)?

Accepted Answer

$J = P 	imes \Delta C$

Question 7

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

Accepted Answer

O$_2$

Question 8

A mutation causes a cell to produce phospholipids with only saturated fatty acid tails. What effect would this have on the membrane at room temperature?

Accepted Answer

The membrane would become less fluid and more rigid.

Question 9

Which of the following is a function of membrane carbohydrates?

Accepted Answer

Cell-cell recognition and signaling.

Question 10

Integral membrane proteins differ from peripheral membrane proteins in that:

Accepted Answer

Integral proteins are embedded within the hydrophobic core of the lipid bilayer.

Question 11

Which of the following best describes facilitated diffusion?

Accepted Answer

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

Question 12

A cell is placed in a solution containing a high concentration of Na$^+$ ions. Which membrane protein would most likely facilitate the rapid movement of Na$^+$ into the cell?

Accepted Answer

Channel protein selective for Na$^+$

Question 13

Which of the following statements about membrane fluidity is correct?

Accepted Answer

Membrane fluidity increases with a higher proportion of unsaturated fatty acids.

Question 14

Which process is described by the movement of water across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration?

Accepted Answer

Osmosis

Question 15

A cell membrane contains aquaporin proteins. What is the primary function of these proteins?

Accepted Answer

Facilitating rapid movement of water molecules across the membrane

Question 16

Which of the following best explains why polar molecules such as glucose require transport proteins to cross the plasma membrane?

Accepted Answer

The hydrophobic core of the membrane impedes the direct passage of polar molecules.

Question 17

Which of the following is NOT a function of proteins found in the plasma membrane?

Accepted Answer

Synthesis of phospholipids

Question 18

A patient with a genetic mutation lacks functional LDL receptor proteins in their cell membranes. What is the most likely consequence?

Accepted Answer

Cholesterol cannot be transported into cells efficiently, leading to high blood cholesterol levels.

Question 19

Which of the following statements about passive transport is correct?

Accepted Answer

Passive transport moves substances down their concentration gradient without energy input.

Question 20

A cell is placed in a solution containing both O$_2$ and glucose. Which molecule will diffuse more rapidly across the pure phospholipid bilayer, and why?

Accepted Answer

O$_2$, because it is small and nonpolar.

Membrane Structure and Function: Study Guide

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