FRQ AP BIO UNIT 4 PROGRESS CHECK
FINAL PAPER SOLUTIONS 2026
QUESTIONS WITH SOLUTIONS GRADED
A+
>> Describe one characteristic of a membrane that requires a channel to be present for chloride ions
to passively cross the membrane. Explain why the movement of chloride ions out of intestinal cells
leads to water loss.
Answer: Chloride ions require a channel protein to cross the membrane because the hydrophobic
interior of the membrane prevents their free diffusion. As chloride ions are transported out of intestinal
cells, the space outside becomes hypertonic, so water moves out of the cells, leading to water loss.
>> a negative control in the experiment.
Answer: An independent variable in the experiment is the presence of cholera toxin. A negative control
in the experiment is sample I, which does not receive GTP or cholera toxin.
>> why the scientists included sample III as a control treatment in the experiment.
Answer: Sample III serves as a control to compare cAMP production with sample IV, which contains
both cholera toxin and GTP. This allows scientists to evaluate whether cholera toxin’s effect on cAMP
production requires GTP and the G protein pathway.
>> the percent change in the rate of cAMP production due to the presence of cholera toxin in sample
IV compared with sample II.
Answer: Cholera toxin increases cAMP production in the presence of GTP, but has no effect on the
production of cAMP in the absence of GTP.
>> this claim.
Answer: If the drug binds to all cholera toxin, the rate of cAMP production will remain at the baseline of
10 pmol per mg adenylyl cyclase per minute. Even with the toxin present, cAMP will not be produced
because the mutant adenylyl cyclase cannot be activated by Gsa. Without activation, chloride ions will
not be secreted.
>> whether the maximum membrane potential of the postsynaptic neuron will increase, decrease, or
stay the same.
Answer: Describe: The neurotoxin will increase the number of action potentials by causing more
acetylcholine to bind to receptors, leading to a greater influx of sodium ions.
>> your predictions.
Answer: Model A: Effective, because acetylcholine is in the synapse and can break it down before it
binds to receptors.
>> whether corn strains I, II, and III differ in their average number of crossovers.
FINAL PAPER SOLUTIONS 2026
QUESTIONS WITH SOLUTIONS GRADED
A+
>> Describe one characteristic of a membrane that requires a channel to be present for chloride ions
to passively cross the membrane. Explain why the movement of chloride ions out of intestinal cells
leads to water loss.
Answer: Chloride ions require a channel protein to cross the membrane because the hydrophobic
interior of the membrane prevents their free diffusion. As chloride ions are transported out of intestinal
cells, the space outside becomes hypertonic, so water moves out of the cells, leading to water loss.
>> a negative control in the experiment.
Answer: An independent variable in the experiment is the presence of cholera toxin. A negative control
in the experiment is sample I, which does not receive GTP or cholera toxin.
>> why the scientists included sample III as a control treatment in the experiment.
Answer: Sample III serves as a control to compare cAMP production with sample IV, which contains
both cholera toxin and GTP. This allows scientists to evaluate whether cholera toxin’s effect on cAMP
production requires GTP and the G protein pathway.
>> the percent change in the rate of cAMP production due to the presence of cholera toxin in sample
IV compared with sample II.
Answer: Cholera toxin increases cAMP production in the presence of GTP, but has no effect on the
production of cAMP in the absence of GTP.
>> this claim.
Answer: If the drug binds to all cholera toxin, the rate of cAMP production will remain at the baseline of
10 pmol per mg adenylyl cyclase per minute. Even with the toxin present, cAMP will not be produced
because the mutant adenylyl cyclase cannot be activated by Gsa. Without activation, chloride ions will
not be secreted.
>> whether the maximum membrane potential of the postsynaptic neuron will increase, decrease, or
stay the same.
Answer: Describe: The neurotoxin will increase the number of action potentials by causing more
acetylcholine to bind to receptors, leading to a greater influx of sodium ions.
>> your predictions.
Answer: Model A: Effective, because acetylcholine is in the synapse and can break it down before it
binds to receptors.
>> whether corn strains I, II, and III differ in their average number of crossovers.
