Question

Define the term digestion. List the food contents that need digestion.

Answer 1

Hint: Digestion is a catabolic process which happens in all the organisms. The process can be explained by knowing the different kinds of biomolecules that are present in organisms and is required by the organisms constantly to survive and grow.

Complete answer:
Digestion is the complex procedure by which the food is broken down into smaller molecules and converted chemically so that it can be easily absorbed by the cells and tissues of the body of an organism for growth, energy and repair.

The food contents that need digestion are carbohydrates, proteins and lipids.
• Carbohydrates digestion happens in the mouth and in the intestine. Carbohydrates can be simple like sugars or complex like starch. The final product of the carbohydrate digestion is the glucose that is formed. The enzymes used in carbohydrate digestion are salivary amylase, pancreatic amylase, lactase, sucrase, maltase etc. Fibre is a carbohydrate that cannot be broken down and digested.
• Proteins get digested in the stomach and in the duodenum by the enzymes - pepsin, trypsin and chymotrypsin. The final product of the protein digestion is amino acids.
• Lipids or fats begin their digestion in the mouth but mainly it is digested in the small intestine by pancreatic lipase and bile from the liver which helps in the emulsification of fats which helps in the absorption of the fatty acids which is the final product of fat digestion.

Additional information:
Digestion is of two types namely, mechanical digestion and chemical digestion. As the name suggests mechanical digestion is the breakdown of food using mechanical energy and processes like biting and chewing. This helps in breaking down bigger molecules to make it easier for chemical digestion to happen. Chemical digestion happens with the help of digestive juices and enzymes. Carbohydrates, proteins and lipids are digested and assimilated with the help of chemical digestion.

Note: The digestive enzymes are mostly secreted in their inactive form. Trypsin is secreted as trypsinogen which is activated by enterokinase to form the active trypsin. Similarly, pepsinogen is secreted by the chief cells in the stomach which is activated into the active pepsin at a very low pH (below two) and chymotrypsinogen is converted to chymotrypsin by trypsin.
Also, DNA and RNA get digested by the deoxyribonuclease (DNase) and ribonuclease (RNase) secreted from the pancreas.