Digestive system

• Break down physically


  1. Chewing

  2. Saliva from salivary glands makes mixture more liquid

  3. Contains salivary amylase

  4. Breaks down carbohydrates

  5. Passes down oesophagus into stomach
• Stomach


  • Produces pepsin which breaks down protein
  • Contracts muscular walls
  • Produces hydrochloric acid which kills bacteria and provides light environment for pepsin
• Food passes into small intestine

  1. Digested food is absorbed into bloodstream

  2. Produces enzymes to aid digestion

  3. Pancreas makes digestive enzymes and pushes them into small intestine in form of pancreatic juices

  4. Gall bladder releases bile
• Bile


  1. Neutralises acid from stomach making pH more ideal for digestive enzymes to function

  2. Emulsifies fats giving them a larger surface area for digestive enzymes to work on
• Digested food absorption

  1. Absorbed across lining of intestine and straight into bloodstream

  2. Villi increase surface area so food can be absorbed into bloodstream more quickly

  3. Single layer of surface cells so nutrients only diffuse a very short distance

  4. Good blood supply maintains concentration gradient
• Undigested food


  1. Passes into large intestine

  2. Excess water is absorbed

  3. Leaving behind faeces

  4. Stored in rectum
• Order of digestive process

  • Food in mouth
  • Chewed and mixed with saliva
  • Passes down oesophagus
  • Passes into stomach
  • Pushed out into small intestine where it mixes with pancreatic juices and bile
  • Continually broken down and digested
  • Once small enough, absorbed into bloodstream
  • Remaining material moves into large intestine where all water is absorbed
  • Leftover material becomes faeces
• Digestive enzymes


  • Amylase (breaks down carbohydrates)
  • Protease (breaks down proteins)
  • Lipase (breaks down fats)
• Enzymes


  Biological catalysts that speed up chemical reactions without being changed or used up in the process

  Enzymes are large proteins with a unique shape that is complementary to the substrate of the reaction they catalyse

  Enzymes work by having an active site that the substrate binds to, allowing the reaction to occur

  Enzymes can be denatured by changes in temperature or pH that alter their shape
• Most chemical reactions are slow, so enzymes are needed to speed them up without requiring a lot of energy