B3

• The purpose of the digestive system is to break down large molecules into smaller, soluble molecules which are then absorbed into the bloodstream. the rate of these reactions is increased by enzymes
• How the digestive system works: Pt.1

  mouth - food is churned

  salivary glands - produces amylase in the saliva

  oesophagus - carries food to the stomach

  stomach - churn food with muscular walls. Produces protease to digest proteins. Produces hydrochloric acid to kill bacteria and give the right pH for enzymes
• How the digestive system works: Pt.2


  pancreas - produces protease,amylase,lipase to release into small intestine

  liver - bile is produced

  gall bladder - stores bile to release into small intestine

  small intestine - digested food is absorbed into blood

  large intestine - excess water is absorbed from food
• Amylase


  made in:

  • small intestine
  • pancreas
  • salivary glands
  • starch - glucose
• Protease 


  proteins - amino acids

  made in:

  • stomach
  • pancreas
  • small intestine
• Lipase 


  lipids - fatty acids and glycerol

  made in:

  • pancreas
  • small intestine
• Carbohydrates


  provide us with fuel that makes all other reactions of life possible

  • made of simple sugars
  • complex sugars are made up of long chains of simple sugar units
• Lipids


  most efficient energy store, important source of energy

  • made of fatty acids and glycerol
  • lipids are fats or oils
• Proteins 


  used for building up the cells and tissues of your body

  • made of long chains of amino acids
• cell - cells are basic building blocks of all living things
• tissue - a group of cells with a similar structure and function
• organ - a combination of tissues carrying out specific functions
• organ system - organs work together within an organ system
• organism - organ systems work together to form whole living organisms
• An enzyme is a biological catalyst that speeds up chemical reactions without being changed or used up - they lower the activation energy required for the reaction to occur
• enzymes are made up of chains of amino acids folded into a globular shape
• enzymes have an active site which the reactants fits into. Enzymes are very specific and will only catalyse on specific reaction
• Enzymes work at specific conditions of pH and temperature. In extremes of pH or temperature the enzyme will denature
• When enzymes denature it means that the bonds holding together the 3D shape of the active site will break and the active site will break and active shape will deform. The substrate will not fit into the active site anymore and the enzyme cannot function
• Increasing the temperature will increase the rate of reaction due to increased collisions between the enzymes and substrates. But if the temperature is too high the enzyme will denature and the active site will change shape and so the substrate will not fit
• The shape of the active site comes from forces between the different parts of the protein molecules, the forces hold the folded chains in place - change in pH affects the forces which changes the shape of the molecule - the active site is lost so the enzyme is no longer a catalyst
• Sugar 


  uses benedict's solution

  • once heated the solution will change from blue-green to yellow-red
• Starch


  uses iodine

  • turns blue-black
• Protein


  uses biuret

  • changes from blue to pink-purple
• Lipids (test)


  uses ethanol

  • when mixed with ethanol, shake it and it becomes cloudy white
• Bile 


  produced in the Liver and stored in the gall bladder

  • an alkaline which neutralises the hydrochloric acid in the stomach
  • emulsifies fats into small droplets
  • fat droplets have larger surface area - rate of digestion is increased
• Rate = 1000/time OR Rate = amount changed/time