The human digestives system (2.2.1)

• The digestive system is made of these organs :
• Glands (salivary and pancreas) which produce digestives juices containing enzymes which break down food
• The stomach produces hydrochloric acid to kill bacteria and provide the optimum pH for the protease enzyme to work
• The small intestine is where soluble molecules are absorbed into the blood.
• The liver produces bile which is stored in the gall bladder, which helps the digestion of lipids
• The large intestine absorbs water from undigested food to produces faeces, this is passed out of your body through the rectum and anus
• Enzymes : biological catalysts (a substance that increases the rate of the reaction without being used up)
• • Enzymes are present in many reactions so they cannot be controlled
• • Enzymes require an optimum pH and temperature because they are proteins
• The optimum temperature is a range around 37 degrees
• Carbohydrases convert carbohydrates into simple sugars
• Protease convert proteins into amino acids
• Lipase convert lipids into fatty acids and glycerol
• Benedicts test for sugars ( turns brick red)
• Iodine test for starch (turns blue black)
• Biuret test for protein (turns purple)
• Emulsion test for lipids (add ethonal which results in a cloudy layer if a lipid is present)
• Bile is produced in the liver and stored in the gallbladder it is then released into the small intestine
• It has two roles :

  It is alkaline to neutralise the hydrochloric acid which comes from the stomach - the enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
• breaks down large drops of fat into smaller ones (emulsfies it) the large the surface area allows lipase to chemically break down the lipid onto glycerol and fatty acid faster