What is assimilation?

Hint:
The utilization of absorbed food substances by tissues of the body is called assimilation. Digestion is the process by which vitamins, minerals, and other chemicals present in the food materials are broken down into simpler forms and then absorbed.

Complete answer:
Assimilation is the process in which the food molecule is used up by the body cells when required. After the breakdown of the food through physical means and breakdown of a complex molecule through chemical processes the end product is absorbed by the different parts of the body.
Digestive system- it consists of the alimentary canal and consists of the following regions which take part in the digestion process: mouth, buccal cavity, oesophagus, stomach, small intestine, large intestine.
Digestion: it is the process in the gastrointestinal tract, by which food is converted into substances that can be utilized by the body.
Absorption is carried out by-
Simple diffusion: glucose, amino acid, chloride ions, etc.
Active transport: sodium and most of the amino acid, glucose.
Facilitated diffusion: fructose, an amino acid.
The Absorption of substances in different parts of the alimentary canal occurs as follows:
Mouth cavity- few drugs
Stomach: simple sugar, water, alcohol.
Small intestine: monosaccharides, amino acids, fatty acids, glycerol, most minerals, and vitamins.
Large intestine: water, vitamins, minerals, and drugs.
 Substances which are unabsorbed and undigested are called faeces, which are passed out of the body.

Note: During digestion, there are some accessory digestive glands that also take part in the process like the salivary gland, liver, and pancreas.
Certain diseases associated with assimilation like marasmus caused due to deficiency in calories and less absorption of proteins, also kwashiorkor caused due to deficiency of protein only.