bioenergetics

• Photosynthesis


  A chemical reaction which takes place in plants, converting carbon dioxide and water into glucose and oxygen using light energy absorbed by chlorophyll
• Photosynthesis


  • It is an endothermic reaction
  • It takes place inside chloroplasts in plant cells
• Photosynthesis


  1. Plants acquire carbon dioxide via diffusion through stomata

  2. Plants absorb water from soil through roots and transport it via xylem

  3. Glucose produced is used for respiration, stored as starch/fat/oils, used to produce cellulose or amino acids
• Limiting factor


  Something which stops the photosynthesis reaction from occurring at a faster rate
• Limiting factors for photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide level
• Increasing temperature


  Increases rate of reaction up to 45°C, then enzymes become denatured
• Increasing light intensity


  Increases rate of reaction because more energy to carry out more reactions
• Increasing carbon dioxide concentration

  Increases rate of reaction because more reactants available
• Investigating effect of light intensity on rate of photosynthesis

  1. Measure 20cm³ sodium hydrogen carbonate solution in boiling tube

  2. Attach pondweed with paper clip

  3. Clamp boiling tube and shine light at different distances

  4. Count bubbles produced in 1 minute

  5. Repeat 3 times for each distance
• Independent variable


  Light intensity
• Dependent variable


  Amount of bubbles produced
• Control variables


  Same amount of time and pondweed
• Bench lamp used to control light intensity, water temperature monitored with thermometer
• Limiting factor


  Depends on environmental conditions - at night it is light intensity, in winter it is temperature, usually carbon dioxide
• Increasing one factor will increase rate until another factor becomes limiting
• Greenhouse


  • Traps sun's radiation as heat to prevent temperature being limiting
  • Artificial lighting can prevent light intensity being limiting
  • Paraffin heater provides carbon dioxide
• Enclosing crops in greenhouse and regulating conditions can be expensive but results in healthier, faster-grown crops with pests/disease controlled
• Respiration


  Chemical reaction in mitochondria to release energy for living functions, can be aerobic or anaerobic
• Anaerobic respiration


  Glucose not completely oxidised, less energy released than aerobic respiration
• In plants and yeast, anaerobic respiration is called fermentation and used in bread-making and beer-brewing
• Inverse square law


  Light intensity is inversely proportional to the square of the distance from the source
• Calculating light intensity using inverse square law

  1. Light intensity ∝ 1 / (distance)²

  2. Example: at 10cm light intensity is 100 units, at 25cm it is 16 units
• During exercise


  • Body needs more energy, so respiration rate increases
  • Heart pumps faster, breathing rate and volume increase to supply more oxygen
  • If not enough oxygen, anaerobic respiration occurs producing lactic acid causing oxygen debt and muscle fatigue
• Metabolism


  Combination of all reactions in a cell or body, using energy from respiration to synthesise new molecules
• Oxygen debt


  Amount of oxygen required by the body to convert built-up lactic acid back into glucose and remove it from respiring cells