Valves in veins assure that 

A. lymph will be formed.
B. blood in veins must flow back to the heart.
C. the flow of blood through veins is regulated.
D. veins will not receive blood that is under too great a pressure.


B. blood in veins must flow back to the heart.

Biology & Microbiology

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A fertilized egg is called a  

A.  zygote B.  ovule C.  oocyte D.  blastocyst

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Oxygen moves from alveoli to the bloodstream ____

a. because the concentration of oxygen is greater in alveoli than in the blood b. mainly due to the activity of carbonic anhydrase in the red blood cells c. against a concentration gradient d. to equal the concentration of CO2 in the blood e. by active transport

Biology & Microbiology

Glucagon is produced by the

a. adrenal cortex. b. adrenal medulla. c. thyroid. d. kidneys. e. pancreas

Biology & Microbiology

Which of the following is the key regulatory enzyme in glycolysis?

a. phosphofructokinase b. pyruvate dehydrogenase c. citrate synthase d. isocitrate dehydrogenase e. PEP carboxylase

Biology & Microbiology