Q: Which equation best represents the selective permeability of a membrane to a solute?

$J = P \times (C_{out} - C_{in})$

Question 1

Which structural feature of phospholipids is responsible for their ability to form bilayers in water?

Accepted Answer

Their amphipathic nature, with hydrophilic heads and hydrophobic tails

Question 2

According to the fluid mosaic model, which statement best describes the movement of proteins and lipids within the plasma membrane?

Accepted Answer

Both proteins and lipids can move laterally within the membrane, but proteins may be anchored and less mobile

Question 3

Which of the following changes would most likely increase the fluidity of a cell membrane at low temperatures?

Accepted Answer

Increasing the proportion of unsaturated fatty acids in phospholipids

Question 4

A scientist observes that a cell membrane is 'too solid' at room temperature. Which adjustment would most likely restore proper fluidity?

Accepted Answer

Increase the percentage of unsaturated fatty acids in the membrane

Question 5

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

Accepted Answer

Because the hydrophobic core of the membrane prevents their passage

Question 6

Which of the following best explains why membrane fluidity is important for cell function?

Accepted Answer

It allows proteins and lipids to move and interact, enabling selective permeability and proper signaling

Question 7

A cell is placed in a cold environment. Which membrane adaptation would help maintain fluidity?

Accepted Answer

Increase the proportion of phospholipids with double bonds in their fatty acid tails

Question 8

Which of the following is a function of membrane proteins?

Accepted Answer

Facilitating the transport of specific molecules across the membrane

Question 9

Which equation best represents the selective permeability of a membrane to a solute?

Accepted Answer

$J = P 	imes (C_{out} - C_{in})$

Question 10

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

Accepted Answer

Cholesterol acts as a fluidity buffer, preventing membranes from becoming too rigid or too fluid

Question 11

A mutation causes a membrane protein to lose its hydrophobic alpha-helices. What is the most likely consequence?

Accepted Answer

The protein will not be able to span the lipid bilayer

Question 12

Which of the following best describes the difference between passive and active transport across membranes?

Accepted Answer

Passive transport does not require energy, while active transport requires energy input, often from ATP

Question 13

Which scenario best illustrates facilitated diffusion?

Accepted Answer

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

Question 14

If a membrane is composed mainly of saturated fatty acids, what property will it most likely exhibit at low temperatures?

Accepted Answer

It will be less fluid and more likely to solidify

Question 15

Which of the following molecules would cross a plasma membrane most easily without a transport protein?

Accepted Answer

O$_2$ (oxygen)

Question 16

A cell in an extreme cold environment is found to have membranes rich in cholesterol and unsaturated fatty acids. What is the adaptive advantage of this composition?

Accepted Answer

It maintains membrane fluidity at low temperatures

Question 17

Which of the following best explains why transverse (flip-flop) movement of phospholipids is rare in biological membranes?

Accepted Answer

It requires the hydrophilic head to pass through the hydrophobic core, which is energetically unfavorable

Question 18

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

Accepted Answer

Synthesizing DNA and RNA

Question 19

Which property of phospholipids allows them to self-assemble into bilayers in water?

Accepted Answer

Their amphipathic nature, with both hydrophilic and hydrophobic regions

Biological Membranes: Structure, Properties, and Function

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