Question 1

Which of the following best describes diffusion across a biological membrane?

Accepted Answer

The spontaneous movement of particles from an area of high concentration to an area of low concentration, not requiring energy.

Question 2

A scientist adds a drop of dye to two beakers: one with hot water and one with cold water. The dye spreads faster in the hot water. Which property of diffusion does this demonstrate?

Accepted Answer

Diffusion rate increases with higher temperature due to increased kinetic energy.

Question 3

Which of the following molecules would diffuse most rapidly across a phospholipid bilayer?

Accepted Answer

O\_2

Question 4

At equilibrium, which of the following statements is true regarding the movement of molecules across a membrane?

Accepted Answer

Molecules continue to move, but there is no net change in concentration on either side.

Question 5

Which of the following best explains why ions such as Na\^+ and Cl\^- cannot diffuse directly through the phospholipid bilayer?

Accepted Answer

They are charged and cannot pass through the hydrophobic core of the membrane.

Question 6

A cell is placed in a solution with a higher concentration of glucose than inside the cell. If the membrane is permeable to glucose, what will happen?

Accepted Answer

Glucose will move out of the cell by diffusion.

Question 7

Which of the following statements about the diffusion of different compounds across a membrane is correct?

Accepted Answer

The diffusion of each compound is independent of the diffusion of others.

Question 8

Which of the following factors would increase the rate of diffusion of a molecule across a biological membrane?

Accepted Answer

Increasing the lipid solubility of the molecule.

Question 9

A patient is given an intravenous solution containing a high concentration of NaCl. If the patient's red blood cells are placed in this solution, what will happen to the movement of Na\^+ ions?

Accepted Answer

Na\^+ ions will not diffuse into the cells without the help of ion channels.

Question 10

Which of the following best describes the term 'gradient' in the context of membrane transport?

Accepted Answer

A difference in concentration of a substance across a membrane.

Question 11

Which of the following scenarios represents movement 'against the gradient'?

Accepted Answer

Na\^+ moving from low concentration inside the cell to high concentration outside the cell.

Question 12

Which of the following equations best represents the relationship between diffusion rate ($$J$$), surface area ($$A$$), concentration difference ($$\Delta C$$), and membrane thickness ($$d$$)?

Accepted Answer

$$J = D \frac{A \Delta C}{d}$$

Question 13

Why can water, despite being polar, diffuse across the plasma membrane?

Accepted Answer

Because water is small enough to pass through the membrane.

Question 14

Which of the following would decrease the permeability of a biological membrane to a particular molecule?

Accepted Answer

Decreasing the molecule's lipid solubility.

Question 15

A cell membrane is described as 'semi-permeable.' What does this mean?

Accepted Answer

Some substances can diffuse across the membrane, while others cannot.

Question 16

Which of the following best explains why glucose diffuses very slowly across the lipid bilayer?

Accepted Answer

Glucose is a large, uncharged, polar molecule.

Question 17

If a cell is placed in a solution where the concentration of a solute is lower outside than inside, in which direction will the solute move by diffusion?

Accepted Answer

From inside to outside the cell.

Question 18

Which of the following is NOT a property of diffusion?

Accepted Answer

It requires energy input from the cell.

Question 19

Which of the following real-life scenarios best illustrates the concept of a concentration gradient?

Accepted Answer

Oxygen moving from the alveoli into the blood in the lungs.

Question 20

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

Accepted Answer

Small, nonpolar molecules have high permeability.

Movement Across Membranes: Diffusion & Gradients

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