Homeostasis and Transport Open Ended Questions:
Answer the following questions to the best of your ability: Make sure you read
each question carefully and provide answers to all of the parts of the question. Do
not leave any question blank.
Question:
A fresh-water paramecium has a salt concentration lower than 1% in the cytosol.
The diagram shows what happens when the paramecium is placed in an external solution.
Explain why this happens, and describe the process involved. Be sure to state what can be
inferred about the salt solution in which the paramecium is placed.
Homeostasis and Transport
(BIO.A.4.1.1) Plasma Membrane
Answer Key:
Rubric:
4
3
2
1
0
pts: Four key elements are present.
pts: Three key elements are present.
pts: Two key elements are present.
pt: One key element is present.
pts: No key elements are present.
Key Elements:
A: The external salt solution has a salt concentration significantly greater than 1%.
OR
Other equivalent statement.
B: Thus there is a concentration gradient across the membrane of the paramecium, with a
higher concentration of solute outside.
OR
Other equivalent statement.
C: Because of the concentration gradient, there is a net movement of water molecules out
of the cell through the membrane (toward the region of lower concentration of solute). This
is a passive process called osmosis.
OR
Other equivalent explanation.
D: As a result of the loss of water, which makes up most of the cytosol, the paramecium
shrivels and shrinks.
OR
Other equivalent statement.
Keywords:
concentration, higher, gradient , water, molecules , diffuse , membrane, shrivel, solute
Question:
The picture shows the transfer of molecules across the cell membrane.
a.
Describe the process by which O2 molecules pass through the membrane.
b.
Explain how the movement of Na+ ions differs from that of O2 molecules.
Answer Key:
Rubric:
2 pts: Two key elements are present.
1 pt: One key element is present.
0 pts: No key elements are present.
Key elements:
A: Oxygen molecules pass through the lipid bilayer of the cell membrane by diffusion, from
the region of higher concentration to the region of lower concentration.
If there is a higher concentration of oxygen outside the cell, the net movement of molecules
is toward the cell interior. This is an example of passive transport.
OR
Other equivalent description.
B: In the case of the sodium-potassium pump in nerve cells, Na+ is maintained at low
concentrations inside the cell and K+ is at higher concentrations. Na+ moves out of the cell
via active transport, which requires energy (ATP). This is an example of active transport. Na
+ move across the cell membrane through specific channel proteins (sodium ion channels).
OR
Other equivalent statement.
Keywords:
diffusion, concentration, nonpolar, channel, protein, lipid, bilayer, active, passive,
concentration, gradient, higher, lower, sodium, pump, energy, ATP, membrane
Question:
The picture shows glucose molecules moving across a cell membrane.
a.
Describe the process by which glucose molecules pass through the cell membrane. Be sure to
state the kind of molecule that allows glucose molecules to pass through.
b.
Explain whether this is an instance of active transport or passive transport.
Answer Key:
Rubric:
3
2
1
0
pts: Three key elements are present.
pts: Two key elements are present.
pt: One key element is present.
pts: No key elements are present.
Key elements:
A: Glucose molecules move by facilitated diffusion across the cell membrane through carrier
proteins.
OR
Other equivalent statement.
B: A glucose molecule binds to the carrier protein at the end of the protein that lies outside
the cell. In response, the shape of the protein changes in such a way that the glucose
molecule can be released from the other end of the protein, inside the cell.
OR
Other equivalent description.
C: This is an instance of passive transport. Facilitated diffusion does not require energy to
be spent to transport molecules.
OR
Other equivalent explanation.
Keywords:
carrier, protein, binding, passive, energy, active, glucose, membrane, shape
Question:
Describe how endotherms like mammals and birds use thermoregulation to maintain
homeostasis in a changing environment.
Answer Key:
Birds and mammals maintain a constant temperature in a changing environment by
negative feedback to maintain a constant value (called the set point). Negative feedback
means that whenever a change occurs in a system, this automatically causes a corrective
mechanism to start, which reverses the original change and brings the system back towards
the set point back. Some responses generate heat and conserve heat others actively cool
the body down.Examples of responses are muscle contraction and shivering in cool
environmental temperatures. Example of responses in warm environmental conditions are
muscle relaxation and sweating.
Keywords:
feedback, thermoregulatory,