B2: organisation

• Digestive enzymes break down large molecules


  1. Into small molecules (amino acids, fatty acids, glycerol, sugars)

  2. These smaller molecules can pass though the walls of the digestive system

  3. So they can be absorbed into the bloodstream
• Amylase


  Made at: mouth, pancreas, small intestine
• Protease


  Made at: stomach, pancreas, small intestine
• Lipase


  Made at: pancreas, small intestine
• Digestive system


  1. Mouth breaks down food, salivary glands are there, amylase produced in saliva

  2. Food taken down into the oesophagus

  3. Stomach churns food, contains acidic HCL which is the optimum for protease, destroys pathogens

  4. Liver: where bile is produced, neutralising stomach acid and emulsifies fats

  5. Bile: emulsifies fats for larger surface area of fat for the enzyme to work on, making digestion faster, stored in the gall bladder before being released into the small intestine

  6. Pancreas: produces protease, amylase, lipase releasing these into small intestine

  7. Produces all enzyme for complete digestion, also where food is absorbed out of digestion system into the blood

  8. Large intestine where excess water is absorbed from food

  9. Rectum: where faeces are stored before going to anus

  10. The products of digestion move into the blood by diffusion down their concentration gradient and by active transport against their concentration gradient
• Food tests


  1. Grind food up using pestle and mortar

  2. Transfer food into beaker and add distilled water

  3. Mix using glass rod

  4. Filter using filter paper and funnel
• Sugars: Benedict's solution


  • Transfer filtered food into a test tube
  • Add droplets of Benedict's solution into test tube
  • Use water bath at 65 degrees and heat up test tube
  • If positive you will see a green to brick red colour change
• Proteins: Biuret reagent


  • Add 5cm^3 of solution into a test tube
  • Add 5cm^3 of biuret
  • If positive you will see a blue to lilac colour change
• The lungs


  1. The air you breathe goes through the trachea

  2. Splits into bronchi (each one is called the bronchus)

  3. The bronchi split into bronchioles

  4. The bronchioles split into alveoli where gas exchange takes place
• Double circulatory system


  • Made up of heart, blood vessels, blood
  • The right side is smaller and for deoxygenated blood
  • Deoxygenated blood comes through the vena cava, goes through the right atrium and it contracts so it can go through the ventricle and out of the heart through the pulmonary artery to the lungs to be oxidised
  • Oxygenated blood comes back through the pulmonary vein, left atrium contracts so blood goes thru ventricles and leaves via the aorta pumping oxygenated blood throughout the body
  • Heart also needs oxygenated blood for energy from respiration, arteries contain coronary arteries branch off the aorta surrounding the heart so it gets all the oxygenated blood it needs
• Capillaries


  • Involved for gas exchange at the tissues, arteries branch into capillaries
  • Their one cell thick for a short diffusion pathway
  • Permeable walls so substances can diffuse in and out
  • Very small
• Arteries


  • Carry blood under pressure
  • Artery walls are thick and elastic
  • Thicker lumen (gap)
  • Thick layers of muscle to make them strong, elastic fibres which make them stretchy and spring back
• Red blood cells


  • Biconcave for a large surface area faster rate of diffusion
  • Hemoglobin which binds to oxygen
  • No nucleus so more space for oxygen to be carried
• Platelets


  • Help blood clots
  • Small fragments of cells, no nucleus
• Plasma


  • White liquid
  • Carries everything in blood
  • Red and WBC's and platelets
  • Glucose and amino acids
  • Carbon dioxide from organs to lungs
  • Urea from liver to kidneys
  • Hormones, proteins, antitoxins and antibodies