Absorption is the process by which substances take in or soak up other materials. This can occur in various contexts, such as when a sponge absorbs water or when plants absorb nutrients from the soil through their roots. In the human body, absorption refers to how the digestive system takes in nutrients from food after it has been broken down. In chemistry, absorption involves the uptake of molecules by a solid or liquid. For example, when a gas is absorbed by a liquid, it becomes part of that liquid's composition. This process is essential in many applications, including water treatment, air purification, and even in the functioning of biological systems.