Question 1

Which of the following best explains why oxygen ($$\mathrm{O_2$}) $$and carbon dioxide ($$\mathrm{CO_2$}) $$can cross the plasma membrane without the assistance of transport proteins?

Accepted Answer

They are small and nonpolar, allowing them to dissolve in the hydrophobic core of the lipid bilayer.

Question 2

A red blood cell is placed in a solution containing both glucose and fructose. Only glucose is transported into the cell at a rapid rate. What property of the glucose transporter explains this observation?

Accepted Answer

The transporter is highly specific and recognizes only glucose, not its structural isomer fructose.

Question 3

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

Accepted Answer

$$\mathrm{CO_2$}$$

Question 4

Why do aquaporins allow water to cross the membrane rapidly but exclude hydronium ions ($$\mathrm{H_3O^+}$$)?

Accepted Answer

Aquaporins are selective based on size and charge, allowing neutral molecules like water but excluding charged ions like hydronium.

Question 5

A mutation causes a cell to lack functional carrier proteins for glucose. What is the most likely consequence?

Accepted Answer

Glucose uptake will be drastically reduced, impairing cellular respiration.

Question 6

Which of the following statements about the fluid mosaic model of membranes is correct?

Accepted Answer

Membranes are composed of a phospholipid bilayer with proteins embedded or associated with the surface, allowing selective permeability.

Question 7

Which of the following best describes the role of carrier proteins in the plasma membrane?

Accepted Answer

They bind specific molecules, change shape, and shuttle them across the membrane.

Question 8

A scientist observes that water moves into a cell much faster than expected based on its polarity. Which structure is most likely responsible for this observation?

Accepted Answer

Aquaporin channel proteins

Question 9

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

Accepted Answer

Synthesizing DNA from RNA templates

Question 10

A cell is placed in an environment with a high concentration of $$\mathrm{Na^+}$$ ions outside and low concentration inside. Which of the following best explains why $$\mathrm{Na^+}$$ ions do not freely diffuse into the cell?

Accepted Answer

$$\mathrm{Na^+}$$ ions are hydrophilic and cannot pass through the hydrophobic core of the lipid bilayer without a transport protein.

Question 11

Which of the following scenarios best illustrates the concept of selective permeability?

Accepted Answer

A cell allows oxygen to enter rapidly but restricts the entry of glucose unless a specific transporter is present.

Question 12

Which of the following statements about the movement of water across cell membranes is correct?

Accepted Answer

Water moves more rapidly across membranes with aquaporins than by simple diffusion through the lipid bilayer.

Question 13

A patient has a genetic mutation that results in nonfunctional aquaporins in kidney cells. What is the most likely physiological effect?

Accepted Answer

The patient will have difficulty reabsorbing water, leading to excessive urination and dehydration.

Question 14

Which of the following best describes why polar molecules such as glucose cross the lipid bilayer slowly?

Accepted Answer

The hydrophobic interior of the membrane impedes the passage of hydrophilic molecules.

Question 15

Which of the following is a real-life example of the importance of selective permeability in human health?

Accepted Answer

Red blood cells rely on specific glucose transporters to efficiently take up glucose for energy production.

Question 16

Which of the following statements about transport proteins is FALSE?

Accepted Answer

Transport proteins allow any molecule to pass through the membrane without discrimination.

Question 17

A cell must expel metabolic waste products while retaining essential nutrients. Which property of the plasma membrane enables this function?

Accepted Answer

Selective permeability

Question 18

Which of the following best explains why ions with a surrounding shell of water have difficulty crossing the plasma membrane?

Accepted Answer

The hydrophobic core of the membrane repels charged, hydrated ions.

Question 19

Which of the following is a multi-step process involving both the lipid bilayer and transport proteins?

Accepted Answer

Regulation of glucose uptake, which requires the lipid bilayer to act as a barrier and a specific carrier protein to facilitate transport.

Membrane Structure and Selective Permeability

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