The countercurrent exchange system found in fish gills maximizes gas exchange efficiency by:
a. producing rapid water flows across the gill surface.
b. allowing water and blood to come in direct contact to maximize oxygen exchange.
c. having a high concentration gradient of oxygen at the start of the capillaries.
d. maintaining a high concentration gradient of oxygen along the entire length of capillaries.
e. decreasing the oxygen content of the blood leaving the gill filaments
d
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The fovea
a. is the blind spot produced by the optic nerve entering the eye. b. is the region of the retina filled with cones that allows the most acute vision. c. is the region of the retina that has the greatest concentration of rods that enable sight under extremely dim conditions. d. focuses light on the retina. e. is the anterior fluid-filled chamber of the eye.
Something that is administered to members of at least one participating group is known as the:
A. potential outcome. B. average treatment effect. C. treatment. D. treatment effect.
The pH scale is a direct measure of the concentration of:
A) hydrogen ions in a solution. B) hydroxide ions in a solution. C) hydrogen atoms in a solution. D) salt in a solution. E) buffers in a solution.