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rhythmical wave-like muscular contractions of a duct in order to cause movement of substances within it.
the process whereby a particular change causes a response which reverses that change.
the muscular tube of the mammalian digestive tract that links the mouth to the stomach.
an organism that helps to spread a disease, but is not infected with the disease.
water that is found on the surface of the earth, e.g. in rivers, streams, and lakes etc.
a molecule that accelerates (speeds up) a chemical reaction, by lowering its activation energy,...