Which term describes the process of a substance taking in another?

The term that describes the process of a substance taking in another is absorption. Absorption involves the process where one substance, typically a liquid or a gas, permeates or becomes integrated into another substance, often a solid, such as when water is absorbed by a sponge or when nutrients are taken up by cells from the surrounding environment.

In contrast, adsorption refers to the process where molecules adhere to the surface of a solid or liquid without being absorbed into it, which is quite different from absorption where the substance is fully taken in. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, and osmosis is a specific type of diffusion that refers to the movement of water across a semipermeable membrane. Therefore, absorption specifically highlights the incorporation of one substance into the bulk of another, making it the correct term for this process.