Alkaloids are considered "expensive" defense compounds to produce because:
A. they contain a lot of carbon, which is costly
for plants to concentrate.
B. they vaporize readily, so they constantly
have to be synthesized.
C. they contain nitrogen, an essential and
often limiting element plants need.
D. they often function in very small
concentrations.
E. they contain proteins, which are very costly
for a plant to produce.
C
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Gene flow ____
a. has a homogenizing influence between two populations b. speeds up the divergence of two populations c. increases the genetic variation between populations
d. is promoted by isolating mechanisms e. promotes inbreeding
Most digestion occurs and most nutrients and water are absorbed in the __________. Fill in the blank(s) with the appropriate word(s)
Which of these are major causes of diarrhea?
A) infection of the lower intestinal tract B) infection of the upper intestinal tract C) hormonal stimulation D) nervous stimulation
Blood flow through vessel A, 1 mm in diameter, occurs with a 10 kPa pressure gradient from one end to the other. Blood flow through vessel B, 2 mm in diameter, occurs with a 1 kPa pressure gradient from one end to the other. Other conditions are identical. Compared to vessel A, blood flow in vessel B is ____.
a. 1/10 as fast b. 1.6 times faster c. 16 times slower d. 10 times faster