B3

• Tissue


  A group of cells with similar structure and function working together
• Organs


  Collections of tissue which all work together to perform a specific function
• Organ systems


  • Digestive system
  • Circulatory system
  • Gas exchange system
• Pancreas & salivary glands


  • Make and release digestive juices containing enzymes to break down food
• Stomach & small intestine

  • Main organs where food is digested
• Enzymes


  Break down large insoluble food molecules into smaller soluble ones
• Small intestine


  • Where soluble food molecules are absorbed into blood
  • Has a large surface area as it is covered in villi
• Faeces


  Material left after digestion that is passed out of the body through the rectum and anus
• Liver


  • Produces bile which helps digestion of lipids
• Lipids


  Most efficient energy store
• Proteins


  Used for building up cells and tissues of the body, made up of long chains of amino acids
• Catalysts


  Speed up chemical reactions without being used up themselves
• Enzymes


  Special biological catalysts that speed up reactions in our body
• Enzymes

  • Each enzyme interacts with a particular substrate (reactant)
  • Enzyme shape is vital for it to function
  • Long chains of amino acids are folded to produce a molecule with an active site that has a unique shape and can bind to a specific substrate molecule
• 'Lock and key' mechanism


  Substrate fits into enzyme's active site, substrate then splits into products which leave the active site and the enzyme is ready to use again
• Enzymes


  Control the metabolism, the sum of all the reactions in a cell or in the body
• When temperature is too high


  Enzymes are denatured
• Enzymes


  Work best at 37 degrees celsius (temperature of human body)
• pH


  Can affect shape of the active site of an enzyme and make it work efficiently or stop it working
• Digestive enzymes


  • Work outside of the cell and are produced by specialised cells in glands and lining of digestive system
• Digestive enzymes

  • Carbohydrase such as amylase (made in salivary glands & pancreas) catalyse the break down carbohydrates into sugars (mouth and small intestine)
  • Protease (produced in stomach, pancreas & small intestine) catalyse the breakdown of protein into amino acids (in stomach and small intestine)
  • Lipase (produced in pancreas & small intestine) catalyse breakdown of lipids into fatty acids & glycerol (happens in small intestine)
• Stomach


  • Produces HCl to provide acidic conditions that some enzymes need to break down food
  • Produces mucus which protects stomach walls from being digested by HCl
• Some enzymes that catalyse digestion


  • Are made in pancreas & small intestine and work best in alkaline environment
• Liver


  • Makes bile which is stored in gall bladder until needed
  • Bile is needed to make acidic liquid from stomach coming into small intestine alkaline and emulsifies fat