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
  • Proteins
  • Lipids (fats)
• Digestion


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

  2. Small molecules can then be absorbed into the bloodstream
• Main organs of the digestive system

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


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


  • Enzymes begin digestion of proteins, contains hydrochloric acid to help enzymes
• Small intestine


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


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


  Catalyze (speed up) chemical reactions in the body
• Enzymes


  • Large protein molecules with a groove called the active site on their surface
  • The active site is where the substrate (molecule to be broken down) attaches
• Enzyme specificity


  The substrate must fit perfectly into the active site of the enzyme (lock and key theory)
• Protein digestion


  Proteases in the stomach, pancreatic fluid and small intestine break down proteins into amino acids
• Carbohydrate (starch) digestion


  Amylase in saliva and pancreatic fluid breaks down starch into simple sugars
• Lipid digestion


  Lipase in the pancreatic fluid and small intestine breaks down lipids into glycerol and fatty acids
• Bile


  • Made in the liver and stored in the gallbladder, not an enzyme but helps speed up lipid digestion by lipase
  • Bile emulsifies (breaks up) large lipid droplets into smaller ones, increasing the surface area for lipase to work on
  • Bile is also alkaline, helping to neutralize stomach acid and create the right conditions for lipase
• Enzyme


  Speeds up chemical reactions by having a groove on their surface called the active site where the substrate (the molecule the enzyme reacts with) fits perfectly into
• Lock and key theory

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

  1. As temperature increases, enzyme activity increases (reaction gets faster)

  2. At optimum temperature, enzyme works at fastest possible rate (maximum frequency of successful collisions between substrate and active site)

  3. As temperature increases past optimum, enzyme activity rapidly decreases to zero (active site is denatured and substrate no longer fits)
• Optimum temperature for most human enzymes

  • 37 degrees Celsius (human body temperature)
• Denatured


  Active site changes shape so substrate no longer fits perfectly
• Effect of pH on enzyme activity

  1. Enzyme has an optimum pH where activity is maximum

  2. If pH is more acidic or more alkaline, activity drops to zero (active site is denatured)
• Enzymes with different optimum pH

  • Protease enzyme in stomach works best at acidic pH
  • Lipase enzyme released from pancreas into small intestine works best at 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
• Testing for carbohydrates (starch and sugars)

  1. Place 2cm3 of food solution in test tube

  2. Add a few drops of iodine solution

  3. If starch present, iodine turns blue-black

  4. Place 2cm3 of food solution in test tube

  5. Add 10 drops of Benedict's solution

  6. Heat in water bath for 5 mins

  7. Green = small amount of sugar, Yellow = more sugar, Brick red = lots of sugar
• Testing for proteins


  1. Place 2cm3 of food solution in test tube

  2. Add 2cm3 of Biuret solution

  3. If protein present, solution turns purple/lilac
• Testing for lipids/fats


  1. Place 2cm3 of food solution in test tube

  2. Add a few drops of distilled water and ethanol

  3. Shake gently

  4. If lipids present, a white cloudy emulsion forms
• All chemicals used are potentially hazardous, so safety goggles must be worn
• The Benedict's test only works for reducing sugars, not non-reducing sugars like sucrose
• 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

  1. Products diffuse rapidly into bloodstream due to large surface area, concentration gradient, and short diffusion path

  2. Any molecules not absorbed by diffusion are absorbed by active transport
• The adaptations of the small intestine allow for rapid absorption of the products of digestion
• Single circulatory system


  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.
• Double circulatory system


  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.
• Heart


  • An organ consisting mainly of muscle tissue
  • Its job is to pump blood around the body
• Chambers of the heart

  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle
• Atria


  Top chambers of the heart