Every cell in the body requires oxygen for respiration so that sufficient energy can be produced. carbon dioxide, a waste product, is also produced and needs to be removed. therefore, the levels of both gases must be regulated. how does this explain the changes in your pulse rate?

It tells us about the push and pull of blood from the body by the heart.

This regulation tells us about the pulse rate because when the heart pulls the  blood from all body parts this is the time for the removal of carbondioxide from the blood but when the heart pushes blood in the arteries. This is the time when the blood is supplied which is rich in oxygen and we hear the heart beat so we can conclude that the regulation of carbondioxide and oxygen tells us about the pulse rate.

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answer; i believe the answer is (polygenic inheritance;

the correct option is option d