The loop of Henle in the nephrons of desert-dwelling kangaroo rats is much longer than the loop of Henle in humans. What is the advantage of this increased length for the kangaroo rat?
A. A longer loop of Henle can generate a
larger concentration gradient, which allows
for the production of a more concentrated
urine.
B. A longer loop of Henle can generate a
smaller concentration gradient, which allows
for the production of a more concentrated
urine.
C. A longer loop of Henle can generate a
larger concentration gradient, which allows
for the production of a less concentrated
urine.
D. A longer loop of Henle can generate a
smaller concentration gradient, which allows
for the production of a less concentrated
urine.
E. None of the answer options is correct.
A
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Several rhizobial species within a cross-inoculation group should be able to grow with particular legume species such as alfalfa. However, the same cross-inoculation group would be unable to associate with another legume species such as peas
Indicate whether the statement is true or false.
The population at right is being subjected to _____
1.directional selection
2.stabilizing selection
3.disruptive selection
4.selection against intermediate forms
Why doesn't every cell in the body respond to every hormone circulating in the bloodstream?
a. Each cell has a limited number of protein channels that shuttle hormones through its membrane. b. Not all hormones can diffuse through all cell membranes. c. The concentration of some hormones is too low to stimulate every cell. d. Each cell has specific surface receptors, which interact only with hormones that they recognize. e. Although all hormones bind to all cell surfaces, some cells lack second messengers for expression.
Steroid hormones usually act via receptors that
a. are coupled to G proteins that activate adenylyl cyclase. b. activate tyrosine kinases. c. bind to DNA. d. activate phospholipase C.