Question 1

Which of the following best explains why phospholipids form bilayers in water?

Accepted Answer

Their hydrophilic heads interact with water, while their hydrophobic tails avoid water, causing the tails to face inward and heads to face outward.

Question 2

A cell membrane is composed primarily of phospholipids with saturated fatty acid tails. What effect would increasing the proportion of unsaturated fatty acid tails have on the membrane?

Accepted Answer

It would increase membrane fluidity and permeability.

Question 3

Which of the following molecules is most likely to diffuse directly through a pure phospholipid bilayer without the aid of a protein?

Accepted Answer

Oxygen ($$O_2)$$

Question 4

Cholesterol is embedded in animal cell membranes. What is its primary function at high temperatures?

Accepted Answer

It stabilizes the membrane by holding phospholipid tails together, reducing fluidity.

Question 5

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

Accepted Answer

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

Question 6

Which of the following best describes facilitated diffusion?

Accepted Answer

Movement of substances from high to low concentration through a membrane protein, without energy input.

Question 7

Which of the following statements about active transport is correct?

Accepted Answer

It requires energy, often in the form of ATP, to move substances against their concentration gradient.

Question 8

A cell is placed in an isotonic solution. What will happen to the movement of water across the cell membrane?

Accepted Answer

There will be no net movement of water, but water molecules will continue to move in both directions.

Question 9

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 cannot pass through the hydrophobic core of the bilayer.

Question 10

Which of the following scenarios would most likely require a carrier protein for transport across the membrane?

Accepted Answer

Movement of glucose into a cell

Question 11

A plant cell is placed in a hypertonic solution. Predict what will happen to the cell and explain why.

Accepted Answer

The cell will lose water and the plasma membrane will pull away from the cell wall (plasmolysis).

Question 12

Which of the following best describes the amphipathic nature of phospholipids?

Accepted Answer

They have both a hydrophilic head and hydrophobic tails.

Question 13

Which of the following changes would most likely increase the permeability of a cell membrane at room temperature?

Accepted Answer

Decreasing the amount of cholesterol in the membrane.

Question 14

Which of the following is a correct statement about osmosis?

Accepted Answer

Osmosis is the movement of water from an area of low solute concentration to an area of high solute concentration.

Question 15

A scientist observes that a certain molecule cannot cross the cell membrane by simple diffusion, but can cross when a specific protein is present. Which type of transport is most likely occurring?

Accepted Answer

Facilitated diffusion

Question 16

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

Accepted Answer

They facilitate the rapid diffusion of water across the membrane.

Question 17

A cell uses ATP to move potassium ions ($$K^+) $$into the cell against their concentration gradient. Which type of membrane transport is this?

Accepted Answer

Active transport

Question 18

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

Accepted Answer

Increasing the proportion of saturated fatty acids.

Question 19

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

Accepted Answer

Synthesizing DNA

Question 20

A cell is placed in a solution and water moves into the cell until it bursts. Which of the following best describes the tonicity of the solution relative to the cell?

Accepted Answer

The solution is hypotonic to the cell.

Phospholipids, Biological Membranes, and Membrane Transport

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