bioenergetics

• Photosynthesis


  An endothermic reaction which converts light energy into chemical energy using simple raw materials
• Photosynthesis


  • Requires chlorophyll, a green pigment found in chloroplasts that absorbs light energy
  • Requires carbon dioxide and water as raw materials
  • Produces glucose which is stored as starch
• Testing a leaf for starch


  1. Place leaf in boiling water

  2. Put leaf in ethanol and stand in boiling water

  3. Wash leaf in cold water

  4. Spread leaf on white tile and cover with iodine

  5. If iodine changes colour to black, starch is present
• The 'Testing a leaf for starch' practical can be used to prove chlorophyll, light and carbon dioxide are required for photosynthesis
• De-starching a plant


  Place plant in the dark for 2-3 days so it uses up all its starch stores
• Limiting factor


  The component of a reaction that is in shortest supply, preventing the rate of reaction increasing
• Light intensity increases


  Rate of photosynthesis increases
• Light intensity continues increasing

  Rate of photosynthesis levels off as another factor (carbon dioxide or temperature) becomes limiting
• Temperature increases from 5°C to 24°C

  Rate of photosynthesis increases, reaching an optimum at 24°C
• Temperature increases above 24°C


  Rate of photosynthesis rapidly decreases as enzymes become denatured
• Measuring the rate of photosynthesis using pondweed

  1. Set up apparatus

  2. Count bubbles produced per minute
• This setup does not provide an accurate measure of the rate of photosynthesis as bubbles may be lost and have different volumes
• Uses of glucose


  • Stored as insoluble starch
  • Used in respiration to release ATP
  • Used to make cellulose for cell walls
  • Manufacture of lipids and oils in seeds
  • Joins with magnesium ions to make chlorophyll
  • Joins with nitrate ions to produce amino acids
• Minerals required for plant growth

  • Nitrate - used to make amino acids and proteins for growth
  • Magnesium - part of the chlorophyll molecule
• Respiration


  The series of exothermic chemical reactions that produce ATP by breaking down nutrient molecules in living cells
• Nutrient molecules broken down in respiration

  • Glucose
  • Lipids
  • Protein
• Aerobic respiration


  • Occurs in the mitochondria in the presence of oxygen
  • Complete breakdown of glucose producing CO2 and H2O
  • High energy yield
• Anaerobic respiration


  • Occurs in the absence of oxygen
  • Incomplete breakdown of respiratory substrate producing CO2 and ethanol (plants/yeast) or lactic acid (animals/bacteria)
  • Low energy yield
• Uses of energy released in respiration

  • Synthesis of biological molecules
  • Digestion
  • Growth
  • Cell division
  • Nervous impulse transmission
  • Muscle contraction
  • Maintenance of constant body temperature
• Exercise increases muscle contraction

  Increases demand for energy, so increases respiration rate
• Increased respiration during exercise


  Increases heart rate, breathing rate and breath volume to supply more oxygenated blood
• Vigorous exercise like sprinting

  Can produce lactic acid in muscles due to insufficient oxygen supply for aerobic respiration
• Lactic acid production in muscles

  Causes stiffness and soreness as it denatures proteins
• After exercise, lactic acid is transported to the liver


  Where it is converted back into glucose using oxygen, known as oxygen debt
• Metabolism


  The sum of all the reactions in a cell or the body, controlled by enzymes and responsible for digestion and synthesis of molecules
• Respiration provides the energy for metabolism, so a higher metabolic rate leads to a higher rate of respiration and greater energy nutrient requirements