Answer:
because they are always doing the same thing
A scenario where a cell may be needed to perform a form of endocytosis is when transporting large molecules. A scenario where a cell may be needed to perform a form of exocytosis is when releasing the large molecule from the cell.
Active muscles demand huge amounts of oxygen, and the circulatory system works hard to provide it. Blood carries oxygen to the muscles. When the body is at rest, blood carries nutrients to the muscles so that they can repair and rebuild themselves. Blood also carries away the waste products that hard-working muscles produce, back out through the lungs to be filtered.
so they Circulatory system xx muscular system :)
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