Importance of the process of digestion in humans:

Our cells require oxygen, water, salts, amino acids, simple sugars, fatty acids, and vitamins. These can cross cell membranes to enter the cells. Amino acids, simple sugars, and fatty acids are rare in our environment. Such substances are usually parts of larger molecules like proteins, polysaccharides, and lipids, which cannot cross the membranes. There is a need of converting such large and non-diffusible molecules into smaller and diffusible molecules that can cross the membranes. This is achieved through the process of digestion.