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small ball of chewed food mixed with saliva that is formed in the mouth, which is swallowed.
a molecule found inside red blood cells that can carry both oxygen and carbon dioxide.
part of cellular respiration: a cyclical series of reactions in which the pyruvic acid formed in...
series of interlinked food chains by which energy circulates within an ecosystem.
(also called secondary thickening) growth due to new cells being formed by the secondary...