Which structure prevents blood flowing back into the heart from the aorta between heartbeats?
A. semilunar valve
B. atrioventricular valve
C. tricuspid valve
D. mitral valve
E. ductus arteriosus
A. semilunar valve
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Which is/are true regarding organic acids?
A. They are weak acids. B. They are often involved in metabolic reactions. C. They often exist in the ionized form at the near-neutral pH found in a cell. D. Pyruvate and pyruvic acid refer to different forms of the same substance. E. All of the choices are true.
At what point in the figure above is the urine
most concentrated? a. A b. B c. C d. D e. none of these
Variations in genes are called ________. Examples of these variations include eye color. There are blue eyes, green eyes, brown eyes, and several combinations of these.
A. polymorphisms B. alleles C. traits D. homeologues
What defines a geological time period known as an era?
A) Location of the continents B) The distinct life forms that were present C) Average global temperature D) The eras represent equal divisions of time