B4 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 equations


  1. Glucose + oxygen → carbon dioxide + water (+energy)

  2. C6H12O6 + 6O2 → 6CO2 + 6H2O (+energy)
• Where aerobic respiration takes place

  In the mitochondria
• Why organisms require the energy released by respiration

  • Synthesis of larger molecules
  • Muscle contraction
  • Maintenance of body temperature
  • Active transport
• Anaerobic respiration


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


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

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


  Can lead to muscle fatigue due to lactic acid build up in muscles, preventing efficient contraction
• 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 equation


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


  It is 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 in the body 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
• How lactic acid is transported away from the muscles (higher)
• Metabolism


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


  The process by which plants make glucose from sunlight
• Endothermic reaction


  Energy is transferred from the environment to the chloroplasts by light
• Photosynthesis


  Carbon dioxide + water → glucose + oxygen
• Factors affecting rate of photosynthesis

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

  
• Measuring oxygen production to calculate rate of photosynthesis

  1. Pondweed in test tube

  2. Capillary tube and syringe

  3. Lamp at measured distance

  4. Measure distance bubble moves to calculate oxygen volume

  5. Control variables except independent variable

  
• Limiting factor


  An environmental condition (such as light intensity) which, in low levels, restricts any increase in the rate of photosynthesis