Homeostasis/Excretory Problem Set
BIO 126 Active Learning (Week 2)
1. To test the hypothesis that mussels are osmoconformers, researchers exposed mussels to water
of varying osmolarities and then drew hemolymph samples from the mussels.
Water Osmolarity Hemolymph Osmolarity
250 261
500 503
750 746
1000 992
Is the researchers' hypothesis supported by the data, shown above?
Values of osmolarity of water and hemolymph, external and internal environments of mussels are close
so hypothesis is supported by the data.
2. You have isolated a segment of a rat nephron and introduced a solution of known composition.
When you compare the fluid collected at the end of the segment with the test solution
introduced at the beginning, you find that the volume has decreased by 30 percent and
the Na+ concentration has decreased by 30 percent, but the urea concentration has increased
by 50 percent.
What processes in this segment might account for these changes?
Choose all that apply
a. reabsorption of urea
b. filtration of Na+
c. reabsorption of Na+
d. filtration of water
e. filtration of urea
f. reabsorption of water
3. Biologists recently have been able to produce mice that lack functioning genes for aquaporins.
How does their urine compare to that of individuals with normal aquaporins?
a) lower volume and higher osmolarity
b) higher volume and lower osmolarity
c) higher volume and higher osmolarity
d) lower volume and lower osmolarity
