Bioenergetics

• Photosynthesis


  The process by which plants synthesise glucose using light energy from the Sun. Light energy is converted into chemical energy.
• Photosynthesis


  Carbon dioxide + water → glucose + oxygen
• Photosynthesis


  An endothermic reaction - energy is transferred from the environment to chloroplasts by light
• Showing that a plant gives off oxygen during photosynthesis


  Using a water plant (eg. Elodea), collect gas bubbles produced during photosynthesis. The gas will relight a glowing splint as it contains oxygen.
• Leaf adaptations that maximise the rate of photosynthesis

  • Broad leaves - maximise surface area
  • Thin leaves - short diffusion distance
  • Chlorophyll present - trap light energy
  • Veins - transport water to leaves via xylem, remove photosynthesis products via phloem
  • Air spaces - allow CO2 to enter and O2 to leave
  • Guard cells - control opening of stomata for gaseous exchange and prevent water loss
• Factors that affect the rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• Increasing temperature


  Increases the rate of photosynthesis as the kinetic energy of particles is increased. The rate decreases past a certain temperature as enzymes become denatured.
• Increasing light intensity


  Increases the rate of photosynthesis until another factor becomes limiting
• Increasing carbon dioxide concentration


  Increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose
• Decreasing the amount of chlorophyll


  Decreases the rate of photosynthesis as chlorophyll is required to absorb light energy
• Limiting factor


  An environmental factor which can restrict the rate of photosynthesis eg. light intensity
• Calculating the rate of photosynthesis by measuring oxygen production

  Set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe). Oxygen gas produced causes the bubble in the capillary tube to move. The distance moved by the bubble is used to calculate the volume of oxygen produced.
• Farmers controlling limiting factors


  They can control temperature, light intensity and CO2 concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield
• Inverse square law


  Light intensity ∝ 1 / distance^2
• Uses of glucose produced during photosynthesis

  • Respiration
  • Starch for storage
  • Cellulose for strength
  • Amino acid and protein synthesis (combined with nitrates)
  • Lipids for energy storage in seeds
• Aerobic respiration


  An exothermic reaction in which glucose reacts with oxygen to release energy which can be used by cells
• Aerobic respiration


  Glucose + oxygen → carbon dioxide + water (+energy)
• Anaerobic respiration


  An exothermic reaction in which glucose is broken down to release energy in the absence of oxygen
• Anaerobic respiration


  Glucose → lactic acid (+energy)
• Anaerobic respiration is less efficient than aerobic respiration
• Reason anaerobic respiration is less efficient

  Glucose is not completely broken down, so less energy is transferred
• Anaerobic respiration


  Leads to muscle fatigue due to lactic acid build up
• Oxygen debt


  The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration
• Fermentation


  A type of anaerobic respiration that occurs in yeast cells
• Fermentation


  Glucose → ethanol + carbon dioxide (+energy)
• Importance of fermentation


  Used in the production of bread and alcoholic drinks
• Differences between aerobic and anaerobic respiration


  • Aerobic requires oxygen; anaerobic does not
  • Aerobic produces CO2 and water; anaerobic produces lactic acid or ethanol + CO2
  • Aerobic transfers a greater amount of energy
• How muscles store glucose

  As glycogen
• Changes when muscular activity increases


  1. Heart rate increases and arteries dilate - increases flow of oxygenated blood to muscles

  2. Breathing rate increases and breathing is deeper - increases the rate of gaseous exchange

  3. Stored glycogen is converted back into glucose
• Lactic acid is transported away from muscles to the liver, where it is oxidised back to glucose
• Metabolism


  The sum of all the reactions that take place in a cell or an organism
• How cells use energy from respiration


  To continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules
• Examples of metabolic reactions


  • Glucose into starch/glycogen/cellulose
  • Glycerol and fatty acids into lipids
  • Glucose and nitrate ions into amino acids
  • Photosynthesis
  • Respiration
  • Breakdown of excess proteins into urea