1. The taking up of liquids by solids or of gases by solids or liquids.
2. The taking up of light or its energy by black or colored rays.
3. The taking up by the body of radiant energy, causing a rise in body temperature.
4. The reduction in intensity of an x-ray photon as it passes through a substance or a beam of light as it passes through a solution (used in clinical photometry as well as nuclear methods).
5. The passage of a substance through some surface of the body into body fluids and tissues, such as the diffusion of oxygen from the alveolar air into the blood, or the active transport of amino acids from food through the epithelium of the small intestine.
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