Question 1

Which of the following best explains why phospholipids spontaneously form bilayers in aqueous environments?

Accepted Answer

The hydrophobic tails avoid water while the hydrophilic heads interact with water, minimizing free energy.

Question 2

A researcher observes that a cell membrane becomes more permeable to water at higher temperatures. Which property of the membrane is most directly responsible for this change?

Accepted Answer

Increased membrane fluidity at higher temperatures.

Question 3

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

Accepted Answer

Oxygen ($$O_2)$$

Question 4

A red blood cell is placed in a hypotonic solution. What will most likely happen to the cell, and why?

Accepted Answer

It will swell and possibly burst because water enters the cell by osmosis.

Question 5

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

Accepted Answer

A membrane composed of a phospholipid bilayer with proteins embedded and moving laterally within it.

Question 6

Which factor would most likely increase the fluidity of a cell membrane?

Accepted Answer

A higher proportion of unsaturated fatty acids in phospholipids.

Question 7

A cell uses a carrier protein to move glucose against its concentration gradient. Which type of membrane transport is this?

Accepted Answer

Active transport

Question 8

Which of the following statements about facilitated diffusion is correct?

Accepted Answer

It requires a transport protein but does not require energy input from the cell.

Question 9

If a cell is placed in a solution where the concentration of solutes is higher outside the cell than inside, what type of solution is this, and what will happen to the cell?

Accepted Answer

Hypertonic; the cell will lose water and shrink.

Question 10

Which of the following best explains why ions such as $$Na^+$$ and $$K^+$$ cannot easily cross the phospholipid bilayer?

Accepted Answer

They are charged and hydrophilic, so they cannot pass through the hydrophobic core of the bilayer.

Question 11

A scientist adds a chemical that increases the proportion of saturated fatty acids in a cell membrane. What is the most likely effect on membrane permeability?

Accepted Answer

Membrane permeability will decrease.

Question 12

Which of the following equations correctly represents the net movement of water during osmosis?

Accepted Answer

$$\Delta \Psi = \Psi_{inside} - \Psi_{outside}$$, where water moves from high to low water potential.

Question 13

Which of the following is a key difference between passive and active transport across cell membranes?

Accepted Answer

Active transport requires energy input, while passive transport does not.

Question 14

A cell is placed in an isotonic solution. What will happen to the cell's volume over time?

Accepted Answer

It will remain the same because there is no net movement of water.

Question 15

Which of the following best describes the role of cholesterol in animal cell membranes at moderate temperatures?

Accepted Answer

It reduces membrane fluidity by restricting phospholipid movement.

Question 16

Which of the following scenarios best illustrates secondary active transport?

Accepted Answer

A sodium gradient established by ATP-driven pumps is used to transport glucose into the cell against its concentration gradient.

Question 17

Which of the following statements about the permeability of the phospholipid bilayer is correct?

Accepted Answer

Small, nonpolar molecules cross easily, while large or charged molecules require transport proteins.

Question 18

A cell is placed in a solution and begins to shrink. Which of the following best explains what is happening?

Accepted Answer

The solution is hypertonic, so water leaves the cell by osmosis.

Question 19

Which of the following best describes the relationship between membrane fluidity and permeability?

Accepted Answer

As membrane fluidity increases, permeability generally increases.

Membrane Structure and Transport: Study Notes for General Biology

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