• Wayne State University

• BIO 2600

ESSENTIAL CELL BIOLOGY, FOURTH EDITION
CHAPTER 12: TRANSPORT ACROSS CELL MEMBRANES
 2014 GARLAND SCIENCE PUBLISHING
Principles of Transmembrane Transport
12-1 Indicate whether the following statements are true or false. If a statement is false, explain
why it is false.
A. CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes.
B. The differences in permeability between artificial lipid bilayers and cell
membranes arise from variations in phospholipid content.
C. Transporters are similar to channels, except that they are larger, allowing folded
proteins as well as smaller organic molecules to pass through them.
D. Cells expend energy in the form of ATP hydrolysis so as to maintain ion
concentrations that differ from those found outside the cell.
A. True.
B. False. The primary difference between cell membranes and artificial membranes
is that cell membranes have proteins responsible for creating a selective
permeability, which varies with the location and function of the membrane.
C. False. Transporters work by changing conformation after specific binding of the
solute to be transported. Channels exclude molecules on the basis of size and
charge, but do not depend on specific recognition of the molecules moving
through.
D. True.
12-2 Which of the following channels would not be expected to generate a change in voltage
by movement of its substrate across the membrane where it is found?

12-3 Although the extracellular environment has a high sodium ion concentration and the
intracellular environment has a high potassium ion concentration, both must be
neutralized by negatively charged molecules. In the extracellular case, what is the
principal anion?

12-4 B. ethanol (polar versus charged)