When you are upright, what is the primary mechanism that propels blood in your feet back to your inferior vena cava?
A. recoil of elastic fibers in the walls of the leg veins
B. contraction of the left ventricle of the heart
C. contraction of smooth muscle in the walls of the leg veins
D. contraction of skeletal muscles in your legs
E. the valves in the leg veins alternating between open and closed
D. contraction of skeletal muscles in your legs
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Which of the following is true regarding the concept of biomagnification?
a. Toxic materials that biomagnify are lost just as energy is lost from a natural system. b. Toxic materials that biomagnify often accumulate in fat tissues of animals. c. Toxic materials that biomagnify become more concentrated as they move up a food chain. d. b and c e. a and b
What does each different band on a DNA profile represent?
Exogenous antigens are processed for immune recognition by ________ cells
A) dendritic B) all nucleated C) macrophage D) helper T E) dendritic and macrophage
Which is incorrect about inducible operons?
Which is incorrect about inducible operons? A) Often encode enzymes for catabolic pathways B) Include the lac operon C) Are normally turned off D) Have genes turned off by a buildup of end product E) Are turned on by the substrate of the enzyme