Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Phospholipids can self-assemble into a
bilayer when placed in water.
Think about why this predictable
structure results, and discuss with a
partner or in a group.
Concept 5.1 Biological Membranes Have a Common Structure and Are Fluid
Phospholipids can self-assemble into a bilayer when
placed in water.
This predictable structure results because:
a. individual phospholipids have a hydrophilic “head”
and a longer, hydrophobic “tail.”
b. they assort themselves so that the hydrophilic ends
don’t contact the water.
c. they assort themselves so that the hydrophilic heads
face inwards, interacting with each other.
d. they assort themselves so that the hydrophobic ends
face inwards, avoiding contact with water.
e. Both a and d
Concept 5.2 Some Substances Can Cross the Membrane by Diffusion, Part 1
Discuss the following scenarios with a partner or with a
group:
• A cucumber placed in a solution of brine (very salty
water), over time turning into a pickle
• A person sitting in a tapwater bath
Osmosis of water by diffusion is the only process occurring
in these two scenarios.
Discuss the direction of the gradient of water flow, and
determine the correct term (e.g., isotonic, hypertonic,
etc.) for the starting condition inside of the cells (plant
cells of the cucumber, and skin cells of the human in the
bath).
Concept 5.2 Some Substances Can Cross the Membrane by Diffusion, Part 1
Consider the process of osmosis for:
• A cucumber placed in a solution of brine (very salty
water), over time turning into a pickle
• A person sitting in a tapwater bath
Which of the following correctly describes the scenarios at
the starting condition?
a. The cucumber is hypotonic with respect to the brine.
b. The human skin cells are hypertonic with respect to
the bathwater.
c. Water begins to flow by osmosis into the cucumber
and out of the human skin cells.
d. Both a and b
e. All of the above
Concept 5.2 Some Substances Can Cross the Membrane by Diffusion, Part 2
Type 2 diabetes, often associated with obesity, results in
an increase in blood-glucose levels. It occurs in humans
as well as in animals, including domestic dogs and cats.
One early sign that a person or animal might be developing
type 2 diabetes is excessive thirst. Discuss a possible
reason for this symptom based on what you have learned
in this chapter about tonicity in cells.
Concept 5.2 Some Substances Can Cross the Membrane by Diffusion, Part 2
Type 2 diabetes, often associated with obesity, results in
an increase in blood-glucose levels. It occurs in humans
as well as in animals, including domestic dogs and cats.
One early sign that a person or animal might be developing
type 2 diabetes is excessive thirst. Consider the following
possible explanation:
Elevated glucose levels in blood would result in water
leaving cells, causing dehydration.
a. True
b. False
c. I don’t know.
Concept 5.3 Some Substances Require Energy to Cross the Membrane
Consider the following statements, and discuss whether
each is correct:
• Simple or facilitated diffusion requires cellular energy.
• Diffusion results in a net flow of solute down a
concentration gradient, while active transport works
against the concentration gradient.
• Secondary active transport uses energy to set up a
concentration gradient which then allows some
passive diffusion to occur, which recaptures some of
the energy expended.
• Membrane proteins are required for all membrane
transport into and out of cells.
Concept 5.3 Some Substances Require Energy to Cross the Membrane
Which of the following statements is/are correct?
a. Simple or facilitated diffusion requires cellular energy.
b. Diffusion results in a net flow of solute down a
concentration gradient, while active transport works
against the concentration gradient.
c. Secondary active transport uses energy to set up a
concentration gradient which then allows some
passive diffusion to occur, which recaptures some of
the energy expended.
d. Membrane proteins are required for all membrane
transport into and out of cells.
e. Both b and c
Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Discuss the validity of the following statement with
a partner or group:
Endocytosis effectively decreases the length of the
plasma membrane of the cell engulfing the large
particle or cell, while exocytosis effectively
increases the length of the plasma membrane of
the cell releasing the large molecules or particles.
Concept 5.4 Large Molecules Cross the Membrane via Vesicles
Endocytosis effectively decreases the length of the
plasma membrane of the cell engulfing the large
particle or cell, while exocytosis effectively
increases the length of the plasma membrane of
the cell releasing the large molecules or particles.
This statement is:
a. True
b. False
c. I don’t know.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental
Signals
Intercellular signaling is somewhat analogous to a lock and
key system. The lock won’t open unless the right key is
used, analogous to the cell needing to have the
appropriate receptor in order to respond to a signal.
Discuss in groups whether this statement is true or false.
Concept 5.5 The Membrane Plays a Key Role in a Cell’s Response to Environmental
Signals
Intercellular signaling is somewhat analogous to a
lock and key system. The lock won’t open unless
the right key is used, analogous to the cell
needing to have the appropriate receptor in order
to respond to a signal.
This statement is:
a. True
b. False
c. I don’t know.
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Think about each of the following statements and discuss
whether they are true with respect to the signaling
cascade stimulated by epinephrine (the G protein–
mediated protein kinase pathway).
• In liver cells, each molecule of epinephrine results in
the liberation of one molecule of blood glucose.
• With respect to epinephrine, the same signal-receptor
binding event always produces the same cellular
response in muscles throughout the body.
• The signaling cascade set off by epinephrine involves
the activation of some enzymes as well as the
inactivation of others.
Concept 5.6 Signal Transduction Allows the Cell to Respond to Its Environment
Which of the following statements are true with respect to
the signaling cascade stimulated by epinephrine (the G
protein–mediated protein kinase pathway).
a. In liver cells, each molecule of epinephrine results in
the liberation of one molecule of blood glucose.
b. With respect to epinephrine, the same signal-receptor
binding event always produces the same cellular
response in muscles throughout the body.
c. The signaling cascade set off by epinephrine involves
the activation of some enzymes as well as the
inactivation of others.
d. Both a and b
e. All of the above