OpenStax Biology 2e Instructor Answer Guide
Biology 2e
Unit 2: The Cell
Chapter 5: Structure and Function of Plasma Membranes
Visual Connection Questions
1. A doctor injects a patient with what the doctor thinks is an isotonic saline solution. The
patient dies, and an autopsy reveals that many red blood cells have been destroyed. Do you
think the solution the doctor injected was really isotonic?
No, it must have been hypotonic as a hypotonic solution would cause water to enter the cells,
thereby making them burst.
2. Injecting a potassium solution into a person’s blood is lethal. This is how capital punishment
and euthanasia subjects die. Why do you think a potassium solution injection is lethal?
Cells typically have a high concentration of potassium in the cytoplasm and are bathed in a high
concentration of sodium. Injection of potassium dissipates this electrochemical gradient. In
heart muscle, the sodium/potassium potential is responsible for transmitting the signal that
causes the muscle to contract. When this potential is dissipated, the signal can’t be transmitted,
and the heart stops beating. Potassium injections are also used to stop the heart from beating
during surgery.
, OpenStax Biology 2e Instructor Answer Guide
3. If the pH outside the cell decreases, would you expect the amount of amino acids
transported into the cell to increase or decrease?
A decrease in pH means an increase in positively charged H+ ions, and an increase in the
electrical gradient across the membrane. The transport of amino acids into the cell will
increase.
Review Questions
4. Which plasma membrane component can be either found on its surface or embedded in the
membrane structure?
a. protein
5. Which characteristic of a phospholipid contributes to the fluidity of the membrane?
d. double bonds in the fatty acid tail
6. What is the primary function of carbohydrates attached to the exterior of cell membranes?
a. identification of the cell
7. A scientist compares the plasma membrane composition of an animal from the
Mediterranean coast with one from the Mojave Desert. Which hypothesis is most likely to be
correct?
b. The cells from the Mojave Desert animal will have a higher cholesterol concentration in the
plasma membranes.
8. Water moves via osmosis _________.
c. from an area with a high concentration of water to one of lower concentration
9. The principal force driving movement in diffusion is the __________.
c. concentration gradient
10. What problem is faced by organisms that live in fresh water?
a. Their bodies tend to take in too much water.
Biology 2e
Unit 2: The Cell
Chapter 5: Structure and Function of Plasma Membranes
Visual Connection Questions
1. A doctor injects a patient with what the doctor thinks is an isotonic saline solution. The
patient dies, and an autopsy reveals that many red blood cells have been destroyed. Do you
think the solution the doctor injected was really isotonic?
No, it must have been hypotonic as a hypotonic solution would cause water to enter the cells,
thereby making them burst.
2. Injecting a potassium solution into a person’s blood is lethal. This is how capital punishment
and euthanasia subjects die. Why do you think a potassium solution injection is lethal?
Cells typically have a high concentration of potassium in the cytoplasm and are bathed in a high
concentration of sodium. Injection of potassium dissipates this electrochemical gradient. In
heart muscle, the sodium/potassium potential is responsible for transmitting the signal that
causes the muscle to contract. When this potential is dissipated, the signal can’t be transmitted,
and the heart stops beating. Potassium injections are also used to stop the heart from beating
during surgery.
, OpenStax Biology 2e Instructor Answer Guide
3. If the pH outside the cell decreases, would you expect the amount of amino acids
transported into the cell to increase or decrease?
A decrease in pH means an increase in positively charged H+ ions, and an increase in the
electrical gradient across the membrane. The transport of amino acids into the cell will
increase.
Review Questions
4. Which plasma membrane component can be either found on its surface or embedded in the
membrane structure?
a. protein
5. Which characteristic of a phospholipid contributes to the fluidity of the membrane?
d. double bonds in the fatty acid tail
6. What is the primary function of carbohydrates attached to the exterior of cell membranes?
a. identification of the cell
7. A scientist compares the plasma membrane composition of an animal from the
Mediterranean coast with one from the Mojave Desert. Which hypothesis is most likely to be
correct?
b. The cells from the Mojave Desert animal will have a higher cholesterol concentration in the
plasma membranes.
8. Water moves via osmosis _________.
c. from an area with a high concentration of water to one of lower concentration
9. The principal force driving movement in diffusion is the __________.
c. concentration gradient
10. What problem is faced by organisms that live in fresh water?
a. Their bodies tend to take in too much water.
