Q: Which equation best represents the rate of simple diffusion across a cell membrane?

$J = P \times A \times (C_1 - C_2)$

Question 1

Which of the following best describes the difference between osmolarity and tonicity?

Accepted Answer

Osmolarity is the total solute concentration (penetrating and non-penetrating), while tonicity describes the effect of non-penetrating solutes on cell volume.

Question 2

A red blood cell is placed in a solution containing 300 mOsm/L of non-penetrating solutes and 100 mOsm/L of penetrating solutes. What will happen to the cell?

Accepted Answer

The cell will remain the same size because tonicity depends only on non-penetrating solutes.

Question 3

Which equation best represents the rate of simple diffusion across a cell membrane?

Accepted Answer

$J = P 	imes A 	imes (C_1 - C_2)$

Question 4

Which of the following molecules is most likely to cross the cell membrane by simple diffusion?

Accepted Answer

Steroid hormone

Question 5

A patient is given an intravenous solution containing only non-penetrating solutes at a concentration lower than that of their blood plasma. What is the expected effect on their red blood cells?

Accepted Answer

Cells will swell and may burst due to water influx.

Question 6

Which type of membrane transport requires energy directly from ATP hydrolysis?

Accepted Answer

Primary active transport

Question 7

The Na+/K+ ATPase pump moves ions in which direction across the cell membrane?

Accepted Answer

3 Na+ out of the cell, 2 K+ into the cell

Question 8

Which of the following best describes facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient via channel or carrier proteins without energy input.

Question 9

A cell uses secondary active transport to import glucose. Which of the following is true about this process?

Accepted Answer

Na+ moves down its concentration gradient, providing energy for glucose to move against its gradient.

Question 10

Which property of carrier-mediated transport explains why increasing substrate concentration eventually does not increase transport rate?

Accepted Answer

Saturation

Question 11

Which of the following is a feature of channel proteins but NOT carrier proteins?

Accepted Answer

They allow rapid movement of ions (up to $10^7$ ions/sec).

Question 12

Which type of vesicular transport is responsible for the uptake of extracellular fluid in a non-selective manner?

Accepted Answer

Pinocytosis

Question 13

A cell is exposed to a solution containing both glucose and galactose. Both are transported by the same GLUT transporter. What phenomenon will occur?

Accepted Answer

Competition

Question 14

Which of the following statements about exocytosis is correct?

Accepted Answer

It is regulated by Ca$^{2+}$ and requires ATP.

Question 15

Which of the following best explains why non-penetrating solutes determine cell volume changes in response to tonicity?

Accepted Answer

Non-penetrating solutes cannot cross the membrane, so water moves to balance their concentration.

Question 16

Which of the following is an example of secondary active transport?

Accepted Answer

Na$^+$-glucose symporter (SGLT)

Question 17

Which of the following is true about the selectivity of ion channels?

Accepted Answer

It is determined by the size of the pore and the charge of amino acids lining the channel.

Question 18

A cell is exposed to a solution with a higher concentration of non-penetrating solutes than its cytoplasm. What is the tonicity of the solution and what will happen to the cell?

Accepted Answer

The solution is hypertonic; the cell will shrink.

Question 19

Which of the following transport mechanisms is most likely to be saturated at high substrate concentrations?

Accepted Answer

Facilitated diffusion via carrier proteins

Cell Membrane Transport: Mechanisms and Principles

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