Red Blood Cells i believe are not part of the immune system. They carry oxygenated blood to the organs of the body
DNA helps scientists to better classify organisms is because each organ has a specific kind of DNA. For an example, brains and hearts have many small types of RNA. So if a scientists see some RNA they know that its a heart or a brain.
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Physical activity is defined as any voluntary bodily movement produced by skeletal muscles that requires energy expenditure. Physical activity encompasses all activities, at any intensity, performed during any time of day or night. It includes exercise and incidental activity integrated into daily activity.
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