Organisation

• Tissue


  A group of cells with a similar structure and function
• Organ


  A group of tissues working together for a specific function
• Organ system


  Organs grouped together to form organisms
• Main nutrients in food

  • Carbohydrates
  • Protein
  • Lipids (fats)
• Digestion

  1. Large food molecules broken down into small molecules by enzymes

  2. Small molecules absorbed into bloodstream
• Digestive system

  • Food chewed in mouth, enzymes in saliva begin digestion
  • Food passes down esophagus into stomach, enzymes and hydrochloric acid digest proteins
  • Food passes into small intestine, pancreas releases enzymes to digest starch, protein and lipids, liver releases bile to aid lipid digestion
  • Small food molecules absorbed into bloodstream in small intestine
  • Fluid passes through large intestine, water absorbed, feces released
• Products of digestion


  Used by body to build new carbohydrates, lipids and proteins, some glucose used in respiration
• Enzymes

  Catalyze chemical reactions, speed them up that never runs out
• Enzymes


  • Large protein molecules
  • Have a groove on their surface called the active site
  • The active site is where the substrate attaches
• Substrate


  The molecule that the enzyme breaks down
• Substrate fits into active site

  Enzyme can break down the substrate
• Substrate does not fit into active site


  Enzyme cannot break down the substrate
• Lock and key theory


  Enzymes are specific, the substrate must fit perfectly into the active site
• Protein digestion


  1. Proteases in stomach, pancreatic fluid and small intestine

  2. Convert proteins to individual amino acids
• Proteins


  Long chains of chemicals called amino acids
• Starch digestion


  1. Carbohydrases, specifically amylase in saliva and pancreatic fluid

  2. Break down starch into simple sugars
• Starch


  Chain of glucose molecules
• Lipid digestion


  1. Lipase in pancreatic fluid and small intestine

  2. Breaks down lipids into glycerol and fatty acids
• Lipids


  Molecule of glycerol attached to three molecules of fatty acids
• Bile


  • Made in the liver, stored in the gallbladder
  • Not an enzyme, but helps speed up lipid digestion by lipase
  • Converts large lipid droplets into smaller droplets, increasing surface area
  • Alkaline, neutralizes stomach acids in small intestine
• Enzyme

  Speeds up chemical reactions by having a groove on their surface called the active site
• Substrate


  The molecule that the enzyme reacts with, fits perfectly into the active site
• Lock and key theory

  The substrate must fit perfectly into the active site
• Effect of temperature on enzyme activity

  1. Gradually increase temperature

  2. Measure enzyme activity (rate of reaction)

  3. Activity increases as temperature increases

  4. Reach optimum temperature

  5. Activity rapidly decreases past optimum temperature
• Optimum temperature


  The temperature at which the enzyme is working at the fastest possible rate, maximum frequency of successful collisions between substrate and active site
• Denaturation


  At high temperatures, the enzyme molecule vibrates and the shape of the active site changes, so the substrate no longer fits perfectly
• Effect of pH on enzyme activity


  1. Change pH

  2. Measure enzyme activity (rate of reaction)

  3. Enzyme has an optimum pH where activity is maximum

  4. Activity drops to zero if pH is too acidic or too alkaline
• Optimum pH


  The pH at which the enzyme works best
• Enzymes with different optimum pH

  • Protease enzyme in stomach (acidic pH)
  • Lipase enzyme from pancreas (alkaline pH)
• Carrying out chemical tests for carbohydrates, proteins and lipids


  1. Grind food sample with distilled water using mortar and pestle to make a paste

  2. Transfer paste to beaker and add more distilled water

  3. Stir to dissolve chemicals

  4. Filter solution to remove suspended food particles
• Carbohydrates


  Include starch and sugars such as glucose
• Testing for starch


  1. Place 2cm of food solution in test tube

  2. Add a few drops of iodine solution

  3. Blue-black colour indicates presence of starch

  4. Orange colour indicates no starch
• Testing for sugars (e.g. glucose)


  1. Place 2cm3 of food solution in test tube

  2. Add 10 drops of Benedict's solution

  3. Heat test tube in hot water bath for 5 minutes

  4. Green colour = small amount of sugar

  5. Yellow colour = more sugar

  6. Brick red colour = a lot of sugar
• Reducing sugars


  • Sugars that the Benedict's test works for (e.g. glucose)
  • Non-reducing sugars (e.g. sucrose) do not work with Benedict's test
• Testing for proteins


  1. Place 2cm3 of food solution in test tube

  2. Add 2cm3 of Biuret solution

  3. Purple/lilac colour indicates presence of protein
• Testing for lipids/fats


  1. Grind food with distilled water using mortar and pestle

  2. Transfer 2cm3 of solution to test tube

  3. Add a few drops of distilled water and ethanol

  4. Shake gently

  5. White cloudy emulsion indicates presence of lipids
• All chemicals used in these tests are potentially hazardous, so safety goggles must be worn
• Ethanol is highly flammable, so no naked flames should be present when testing for lipids
• Small intestine


  The part of the digestive system where the products of digestion are absorbed into the bloodstream
• Small intestine


  • Very long (around 5 meters in humans)
  • Covered with millions of villi
  • Villi have micro villi that further increase surface area
  • Villi have a good blood supply to rapidly remove products of digestion
  • Villi have a thin membrane to ensure a short diffusion path