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

Biology & Microbiology

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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.

Biology & Microbiology

At what point in the figure above is the urine

most concentrated? a. A b. B c. C d. D e. none of these

Biology & Microbiology

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

Biology & Microbiology

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

Biology & Microbiology