absorb

Absorb means to take in something through or into a surrounding medium, or to take in energy or substances and incorporate them within. In everyday use, a sponge absorbs water; a towel absorbs moisture from a damp surface. Living organisms rely on absorption to take in nutrients, gases, and water; plant roots absorb water and minerals from soil, and animal and human cells absorb nutrients across membranes.

In physics and chemistry, absorption describes the uptake of energy or particles into the interior of a material, often with a change in energy state. This concept is distinct from adsorption, where substances adhere to a surface rather than penetrate. For electromagnetic radiation, absorption depends on the material’s properties and the wavelength; the fraction absorbed is described by the absorption coefficient and, in solution, by the Beer–Lambert law. In spectroscopy, measuring how much light is absorbed reveals concentration and composition.

In biology and medicine, absorption refers to how substances cross biological barriers. Nutrients are absorbed in the digestive tract, while drugs may be absorbed into the bloodstream after oral administration. Absorption can be influenced by surface area, permeability, and first-pass metabolism, which can alter bioavailability.

In environmental and materials contexts, absorption also affects heat, sound, and moisture. Materials with high thermal or acoustic absorption take in energy, reducing heat transfer or sound reflection. In environmental science, soils, water, and organic matter absorb pollutants to varying extents, influencing contaminant fate and remediation strategies.