3.7

• Hydrochloric acid


  Helps make digestion more efficient
• Bile


  Helps make digestion more efficient
• Breaking down protein


  1. Add pepsin, hydrochloric acid, and mixture of both to meat in test tubes

  2. Observe what happens
• Digestive system produces many enzymes that speed up breakdown of food</b>
• Enzymes work best at 37°C, body's steady temperature
• pH


  Needs to be kept at optimum levels for different enzymes to work best
• Protease enzyme in stomach

  Works best in acidic conditions
• Proteases in pancreas


  Work best in alkaline conditions
• Stomach produces hydrochloric acid and pepsin


  1. Acid allows stomach protease enzymes to work effectively

  2. Kills most bacteria in food
• Stomach mucus


  Protects stomach lining from acid and enzymes
• Stomach ulcer


  Mucus is lost, acid production may increase, lining is attacked by acid and enzymes
• Food leaves stomach


  1. Moves into small intestine

  2. Enzymes from pancreas and small intestine work best in alkaline environment
• Bile


  • Green-yellow alkaline liquid produced by liver, stored in gall bladder, released through bile duct
  • Neutralises acid from stomach
  • Emulsifies fats
• Lipase enzymes


  Need large surface area of fats to work on
• Bile emulsifies fats


  1. Breaks up large fat droplets into smaller droplets

  2. Increases surface area for lipase enzymes
• Gall stones can block gall bladder and bile ducts, reducing digestion efficiency
• Hydrochloric acid gives stomach low pH for protease enzymes to work efficiently
• Bile neutralises acid and gives high pH for pancreas and small intestine enzymes to work well
• Bile is not an enzyme, it emulsifies fat to increase surface area for lipase