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
• 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. 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 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
• Absorption of products of digestion in the small intestine


  1. Diffusion of molecules that can be absorbed by diffusion

  2. Active transport of molecules that cannot be absorbed by diffusion
• The adaptations of the small intestine allow for a rapid rate of diffusion of the products of digestion into the bloodstream
• The small intestine is adapted to absorb the products of digestion
• Circulatory system in fish

  Deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated, the oxygenated blood then passes straight from the gills to the organs where the oxygen diffuses out of the blood and into the body cells, the blood now returns to the heart
• Problem with single circulatory system in fish


  The blood loses a lot of pressure as it passes through the gills before reaching the organs, this means the blood travels to the organs relatively slowly so it cannot deliver a great deal of oxygen
• Circulatory system in humans


  Deoxygenated blood is pumped from the heart to the lungs where it collects oxygen, this oxygenated blood then returns to the heart, the heart now pumps the oxygenated blood to the organs where the blood transfers its oxygen to the body cells, the blood now returns back to the heart
• Benefit of double circulatory system in humans


  Because the blood passes through the heart twice, it can travel rapidly to the body cells delivering the oxygen that the cells need
• Heart


  • An organ consisting mainly of muscle tissue
  • The job of the heart is to pump blood around the body
• Heart chambers


  4 chambers - left atrium, right atrium, left ventricle, right ventricle