chemical

• Uses enzymes to break large, complex molecules into smaller, simpler molecules, small enough to be absorbed into bloodstream
• Chewed food is mixed with saliva, a fluid excreted into the mouth cavity by three pairs of salivary glands, which contains mucus that lubricates the mouth and food, holding it in a lump for swallowing. it also contains salivary amylase, an enzyme which begins starch digestion into maltose 
• in the stomach, it occurs through enzymes in gastric juice, pepsin which breaks bonds between certain amino acids, turning protein (long chains of amino acids) into polypeptides (shorter chain). it also breaks down DNA and RNA
• in the small intestine, chemical digestion is achieved through : pancreatic and intestinal juice
• hydrochloric acid also kills bacteria that enters the stomach with the food and activates the pepsin
• Pancreatic juice is secreted by the pancreas via the pancreatic duct. it enters the duodenum through the common bile duct and helps neutralise acid that has come with the material from the stomach
• pancreatic juice contains enzymes involved in digestion :

  • pancreatic amylase - starch into maltose
  • trypsin - protein into peptides
  • pancreatic lipases - fats into fatty acids and glycerol
  • ribonuclease + deoxyribonuclease - digests RNA and DNA
• intestinal juices contains enzymes that complete digestion of carbohydrates, proteins and lipids :

  • Peptidase - peptides into amino acids
  • Sucrase - sucrose
  • Lactase - lactose
  • Maltase - maltose into glucose, fructose, galactose
  • Lipases - lipids into fatty acids and glycerol
• Bacteria in the large intestine breaks down much of the remaining organic compounds