Answer:
Cellular respiration, which generates ATP in your cells, requires oxygen to take place, also, it generates CO2 as a waste product. The respiratory system allows oxygen to diffuse into your blood, and carbon dioxide to diffuse out. The blood then carries the oxygen to the cells, so cellular respiration to continue. When the blood reaches the cells, it also takes the carbon dioxide out of the cells, and carries it to the lungs to get rid of it.
A) A flap in the heart located between each atrium and ventricle.
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The instructive igneous rock is formed from cooling molten rock :)
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I think it depends on what it is about.. Did your teacher give you a punnett square or anything like that?