Question 1

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

Accepted Answer

Their amphipathic nature, with hydrophilic heads and hydrophobic tails

Question 2

A scientist observes that a cell membrane becomes more rigid at lower temperatures. Which change in membrane composition would best counteract this effect and maintain fluidity?

Accepted Answer

Increasing the proportion of unsaturated fatty acids in the phospholipids

Question 3

Which of the following best describes the 'fluid mosaic model' of biological membranes?

Accepted Answer

A membrane is a fluid lipid bilayer with proteins embedded and moving laterally within it

Question 4

Why do ions and polar molecules generally require transport proteins to cross the plasma membrane?

Accepted Answer

Because the hydrophobic core of the lipid bilayer impedes their passage

Question 5

Which of the following scenarios best illustrates facilitated diffusion?

Accepted Answer

Glucose moving into a cell through a specific carrier protein down its concentration gradient

Question 6

A cell is placed in a solution containing a high concentration of a small, nonpolar molecule. Which of the following is most likely to occur?

Accepted Answer

The molecule will diffuse rapidly across the membrane without the need for a transport protein

Question 7

Which equation best represents the rate of simple diffusion across a membrane, according to Fick's Law?

Accepted Answer

$$ J = -D \frac{dC}{dx} $$

Question 8

Which of the following best explains why cholesterol acts as a 'fluidity buffer' in animal cell membranes?

Accepted Answer

Cholesterol disrupts the regular packing of phospholipids, increasing fluidity at low temperatures and decreasing it at high temperatures

Question 9

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

Accepted Answer

Storing genetic information

Question 10

A researcher observes that a certain molecule crosses the plasma membrane only when a specific protein is present, and the process does not require ATP. Which type of transport is most likely involved?

Accepted Answer

Facilitated diffusion

Question 11

Which of the following statements about membrane fluidity is correct?

Accepted Answer

Membranes with a higher proportion of unsaturated fatty acids are more fluid than those with more saturated fatty acids

Question 12

Which of the following best describes selective permeability in biological membranes?

Accepted Answer

Some substances cross the membrane more easily than others due to the structure and composition of the membrane

Question 13

A patient is diagnosed with a genetic disorder that affects the structure of their membrane proteins. Which of the following cellular processes is most likely to be directly impaired?

Accepted Answer

Transport of specific molecules across the plasma membrane

Question 14

Which of the following molecules would most likely require a transport protein to cross the plasma membrane?

Accepted Answer

Na$$^+$$ ion

Question 15

Which of the following best explains why most membrane lipids and some proteins can move laterally within the membrane but rarely flip-flop transversely?

Accepted Answer

The hydrophilic and hydrophobic regions of the molecules make transverse movement energetically unfavorable

Question 16

Which of the following is an example of active transport?

Accepted Answer

The sodium-potassium pump moving Na$$^+$$ out of and K$$^+$$ into a cell using ATP

Question 17

Which of the following best describes the role of integral membrane proteins?

Accepted Answer

They span the lipid bilayer and are involved in transport, signaling, and cell recognition

Question 18

A cell is exposed to a toxin that rigidifies its plasma membrane. Which of the following is a likely consequence?

Accepted Answer

Decreased ability to transport materials and respond to environmental changes

Question 19

Which of the following statements about the plasma membrane is correct?

Accepted Answer

It is a stable boundary that separates a living cell from its surroundings and is composed of a fluid mosaic of lipids and proteins

Biological Membranes: Structure, Composition, and Fluidity

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