The heart is an example of an organ or a muscle.
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There are two kinds of digestion: mechanical and chemical. Mechanical digestion involves physically breaking the food into smaller pieces. Mechanical digestion begins in the mouth as the food is chewed. Chemical digestion involves breaking down the food into simpler nutrients that can be used by the cells.
Aerobic exercise stimulates the heart rate and breathing rate to increase in a way that can be sustained for the exercise session. In contrast, anaerobic ("without oxygen") exercise is activity that causes you to be quickly out of breath, like sprinting or lifting a heavy weight.
