Q: Which equation best describes the net movement of water during osmosis across a semipermeable membrane?

$\text{Water moves from regions of low solute concentration to regions of high solute concentration}$

Question 1

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

Accepted Answer

Phospholipids are amphipathic, with hydrophilic heads that interact with water and hydrophobic tails that avoid water.

Question 2

A cell is placed in a solution and water moves out of the cell by osmosis, causing the cell to shrink. What type of solution is the cell in?

Accepted Answer

Hypertonic solution

Question 3

Which of the following statements about saturated and unsaturated fatty acids is correct?

Accepted Answer

Saturated fatty acids have only single bonds between carbon atoms and pack tightly together.

Question 4

How does the presence of cholesterol affect the permeability of a cell membrane at normal physiological temperatures?

Accepted Answer

Cholesterol decreases membrane permeability by increasing the density of the hydrophobic section.

Question 5

Which equation best describes the net movement of water during osmosis across a semipermeable membrane?

Accepted Answer

$	ext{Water moves from regions of low solute concentration to regions of high solute concentration}$

Question 6

A researcher adds a large amount of unsaturated phospholipids to a synthetic membrane. What is the most likely effect on membrane fluidity and permeability?

Accepted Answer

Membrane fluidity and permeability will increase due to kinks in the tails preventing tight packing.

Question 7

Which of the following best describes the role of membrane proteins in facilitated diffusion?

Accepted Answer

They provide channels or carriers that allow specific molecules to move down their concentration gradient without energy input.

Question 8

Which of the following is a correct statement about the sodium-potassium pump?

Accepted Answer

It requires ATP to transport Na$^+$ out of the cell and K$^+$ into the cell against their concentration gradients.

Question 9

A cell membrane is composed of both lipids and proteins. Which model best describes the current understanding of membrane structure?

Accepted Answer

The fluid-mosaic model, with proteins embedded within and associated with the lipid bilayer.

Question 10

Which of the following molecules would most rapidly cross a pure phospholipid bilayer without the aid of membrane proteins?

Accepted Answer

O$_2$

Question 11

A vesicle containing pure water is placed in a solution with a high concentration of solute. What will happen to the vesicle?

Accepted Answer

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

Question 12

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

Accepted Answer

Catalyzing all chemical reactions in the cell

Question 13

Which of the following best describes secondary active transport (cotransport)?

Accepted Answer

It uses the energy stored in an electrochemical gradient to move another molecule against its gradient.

Question 14

Which of the following statements about membrane fluidity is correct?

Accepted Answer

Membrane fluidity decreases as temperature decreases because phospholipids pack more tightly.

Question 15

Which of the following is a real-world consequence of hydrogenating unsaturated oils?

Accepted Answer

The oils become more solid at room temperature due to the addition of hydrogen atoms and removal of double bonds.

Question 16

Which of the following best explains why ions such as Na$^+$ and K$^+$ require transport proteins to cross the cell membrane?

Accepted Answer

Ions are charged and cannot pass through the hydrophobic core of the lipid bilayer without assistance.

Question 17

Which of the following is a correct description of a phospholipid?

Accepted Answer

A molecule with a hydrophilic head and two hydrophobic tails.

Question 18

Which of the following is a consequence of increasing the proportion of saturated fatty acids in a cell membrane?

Accepted Answer

The membrane becomes less fluid and less permeable due to tighter packing.

Question 19

Which process is described by the equation $J = -D \frac{dC}{dx}$, where $J$ is the flux, $D$ is the diffusion coefficient, and $\frac{dC}{dx}$ is the concentration gradient?

Accepted Answer

Simple diffusion

Chapter 6: Lipids, Membranes, and the First Cells – Structure, Function, and Transport

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