Question 1

Which property of O$$_2$$ and CO$$_2$$ allows them to cross the lipid bilayer of a cell membrane without the aid of membrane proteins?

Accepted Answer

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

Question 2

Why do ions such as Na$$^+$$ and Cl$$^-$$ require transport proteins to cross the plasma membrane?

Accepted Answer

Because their hydrophilic nature prevents them from passing through the hydrophobic core of the membrane.

Question 3

A glucose carrier protein in red blood cells transports glucose across the membrane much faster than glucose can pass through on its own. What property of this protein explains this specificity?

Accepted Answer

It is specific for glucose and rejects even structural isomers like fructose.

Question 4

Which of the following best describes the role of aquaporins in the cell membrane?

Accepted Answer

They provide a hydrophilic channel that allows rapid movement of water molecules across the membrane.

Question 5

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

Accepted Answer

O$$_2$$

Question 6

A mutation causes a cell to lack aquaporins. What is the most likely consequence?

Accepted Answer

Water will cross the membrane much more slowly.

Question 7

Which of the following statements about selective permeability is correct?

Accepted Answer

The membrane allows some substances to cross more easily than others.

Question 8

A researcher observes that a certain channel protein allows glycerol but not H$$_3O$^+ to $$pass through, even though H$$_3O$^+ is $$smaller. What is the most likely explanation?

Accepted Answer

The channel protein is selective based on charge and chemical properties, not just size.

Question 9

Which of the following best explains why water, a small polar molecule, crosses the membrane more slowly than O$$_2$$?

Accepted Answer

Water is polar and interacts unfavorably with the hydrophobic core of the membrane.

Question 10

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

Accepted Answer

Synthesizing phospholipids for the membrane

Question 11

A cell is placed in a solution containing a high concentration of Na$$^+$$ ions. Which mechanism would most likely be used to move Na$$^+$$ into the cell?

Accepted Answer

Facilitated diffusion through a channel protein

Question 12

Which of the following best describes the fluid mosaic model of the plasma membrane?

Accepted Answer

A dynamic structure with proteins and lipids moving laterally within the layer

Question 13

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

Accepted Answer

A cell allows glucose to enter but prevents Na$$^+$$ from entering without a specific protein.

Question 14

Which of the following would most likely increase the rate of water movement across a cell membrane?

Accepted Answer

Increasing the number of aquaporin proteins in the membrane

Question 15

Which of the following is a real-world example of selective permeability in action?

Accepted Answer

Kidney cells reabsorbing water through aquaporins to concentrate urine

Membrane Structure and Selective Permeability

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