Q: Which equation correctly represents the net movement of ions by the sodium-potassium pump per ATP hydrolyzed?

$$3\ \mathrm{Na}^+_{\text{in}} \rightarrow 3\ \mathrm{Na}^+_{\text{out}};\ 2\ \mathrm{K}^+_{\text{out}} \rightarrow 2\ \mathrm{K}^+_{\text{in}}$$

Q: Which equation best represents the electrochemical gradient that drives ion movement across membranes?

$$\text{Electrochemical gradient} = \text{chemical gradient} + \text{electrical gradient}$$

Question 1

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

Accepted Answer

Their hydrophilic heads interact with water, while hydrophobic tails avoid water, leading to spontaneous bilayer formation.

Question 2

A mutation causes a cell to produce only saturated fatty acids in its membrane phospholipids. What is the most likely effect on membrane fluidity at low temperatures?

Accepted Answer

Membrane fluidity will decrease because saturated tails pack closely, making the membrane more rigid.

Question 3

Which equation correctly represents the net movement of ions by the sodium-potassium pump per ATP hydrolyzed?

Accepted Answer

$$3\ \mathrm{Na}^+_{	ext{in}} ightarrow 3\ \mathrm{Na}^+_{	ext{out}};\ 2\ \mathrm{K}^+_{	ext{out}} ightarrow 2\ \mathrm{K}^+_{	ext{in}}$$

Question 4

Which property of cholesterol allows it to act as a 'fluidity buffer' in animal cell membranes?

Accepted Answer

It increases membrane fluidity at high temperatures and decreases it at low temperatures.

Question 5

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

Accepted Answer

CO$$_2$$

Question 6

A cell is placed in a hypotonic solution. What will happen to the cell if it cannot actively pump out ions?

Accepted Answer

It will swell and may burst due to water influx.

Question 7

Which of the following best describes the role of membrane proteins in the fluid-mosaic model?

Accepted Answer

Membrane proteins are embedded in the bilayer and can move laterally, contributing to membrane fluidity and function.

Question 8

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It moves substances down their concentration gradient via specific membrane proteins.

Question 9

Which factor would most increase the rate of simple diffusion of a solute across a membrane?

Accepted Answer

Decreasing the solute's size

Question 10

Which of the following is a function of carbohydrates attached to membrane proteins and lipids?

Accepted Answer

Cell recognition and adhesion

Question 11

A researcher observes that a membrane protein spans the entire lipid bilayer and contains multiple alpha-helices. This protein is most likely:

Accepted Answer

A transmembrane protein

Question 12

Which of the following best describes the difference between simple diffusion and active transport?

Accepted Answer

Simple diffusion moves substances down their concentration gradient without energy input, while active transport moves substances against their gradient using energy.

Question 13

Which equation best represents the electrochemical gradient that drives ion movement across membranes?

Accepted Answer

$$	ext{Electrochemical gradient} = 	ext{chemical gradient} + 	ext{electrical gradient}$$

Question 14

Which of the following is true about aquaporins?

Accepted Answer

They are water channels that massively increase water permeability while excluding ions.

Question 15

Which process is most likely to be energy-dependent and involve the cytoskeleton?

Accepted Answer

Bulk transport of large proteins via endocytosis

Question 16

A cell is exposed to a toxin that disrupts clathrin-coated pits. Which process will be most directly affected?

Accepted Answer

Receptor-mediated endocytosis of LDL cholesterol

Question 17

Which of the following statements about membrane asymmetry is correct?

Accepted Answer

Carbohydrates are found only on the extracellular side of the membrane.

Question 18

Which factor would decrease the rate of passive diffusion of a solute across a membrane?

Accepted Answer

Increasing membrane thickness

Question 19

Which of the following best describes the function of the fluid-mosaic model?

Accepted Answer

It describes membranes as dynamic structures with lipids and proteins that move laterally, allowing flexibility and selective permeability.

General biology unit 7

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