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 an organism
• 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
• Main organs of the digestive system

  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Liver
  • Pancreas
• Mouth


  • Food chewed, enzymes in saliva begin to digest starch
• Stomach


  • Enzymes begin digestion of proteins, contains hydrochloric acid to help enzymes, churning action turns food into fluid
• Small intestine


  • Enzymes from pancreas and liver continue digestion of starch, protein and lipids
  • Small food molecules absorbed into bloodstream
• Large intestine


  • Water absorbed into bloodstream, feces released from body
• Products of digestion used by body to build new carbohydrates, lipids and proteins
• Some glucose produced used in respiration
• Enzymes


  Catalyse chemical reactions, speed them up
• 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 substrate
• Substrate does not fit into active site


  Enzyme cannot break down 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 (chain of glucose molecules) into simple sugars
• Lipid digestion


  1. Lipase in pancreatic fluid and small intestine

  2. Break down lipids (glycerol attached to fatty acids) 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
• Bile


  Converts large lipid droplets into smaller droplets, increasing surface area for lipase
• Bile


  Alkaline, neutralizes stomach acids, creates alkaline conditions in small intestine to increase lipase activity
• 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. Alter 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)
• 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 to further increase surface area
  • Good blood supply to remove products of digestion
  • Thin membrane under villi for short diffusion path
• Absorption of products of digestion in small intestine

  1. Diffusion of molecules into bloodstream

  2. Active transport for molecules that cannot be absorbed by diffusion
• The features of the small intestine enable a rapid rate of diffusion of the products of digestion into the bloodstream
• Fish have a single circulatory system where deoxygenated blood is pumped from the heart to the gills, becomes oxygenated, and then passes straight to the organs