Chemical Digestion | Biology for GCSE/IGCSE - Year 11 PDF Download

Stages of food breakdown

Food ingested into the body undergoes five distinct stages as it moves through the alimentary canal (the gut):

• Ingestion: Ingestion refers to the intake of substances, such as food and drink, into the body through the mouth.
• Mechanical Digestion: This process involves the physical breakdown of food into smaller pieces without altering the chemical composition of the food molecules. For example, chewing food in the mouth is a form of mechanical digestion.
• Chemical Digestion: Chemical digestion is the process by which large, complex molecules are broken down into smaller, more soluble molecules through the action of enzymes and acids. An example is the breakdown of starch into glucose in the presence of amylase in the saliva.
• Absorption: Absorption is the movement of small food molecules and ions through the intestinal wall into the bloodstream for transport to cells throughout the body. For instance, nutrients like glucose and amino acids are absorbed in the small intestine.
• Assimilation: Assimilation involves the uptake of digested food molecules by cells in the body, where they are utilized for various metabolic processes. An example is the absorption of glucose by cells to produce energy.
• Egestion: Egestion is the elimination of undigested or unabsorbed food material from the body in the form of feces through the anus.

The primary objective of chemical digestion is to break down complex food molecules into smaller, soluble forms that can be easily absorbed by the body.