BIOENERGETICS

• Photosynthesis


  An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light
• Photosynthesis is represented by the equation: carbon dioxide + water -> light -> glucose + oxygen
• Factors affecting the rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• These factors interact and any one of them may be the factor that limits photosynthesis
• Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit
• Students should be able to explain graphs of photosynthesis rate involving two or three factors and decide which is the limiting factor
• Students should understand and use inverse proportion – the inverse square law and light intensity in the context of photosynthesis
• Uses of glucose from photosynthesis

  • Used for respiration
  • Converted into insoluble starch for storage
  • Used to produce fat or oil for storage
  • Used to produce cellulose, which strengthens the cell wall
  • Used to produce amino acids for protein synthesis
• To produce proteins, plants also use nitrate ions that are absorbed from the soil
• Aerobic respiration


  Glucose + oxygen → carbon dioxide + water
• Anaerobic respiration in muscles

  Glucose → lactic acid
• Anaerobic respiration in plant and yeast cells

  Glucose → ethanol + carbon dioxide
• Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcoholic drinks
• During exercise the human body reacts to the increased demand for energy

  1. Heart rate, breathing rate and breath volume increase to supply the muscles with more oxygenated blood

  2. If insufficient oxygen is supplied anaerobic respiration takes place in muscles, causing a build up of lactic acid and creating an oxygen debt

  3. During long periods of vigorous activity muscles become fatigued and stop contracting efficiently
• (HT only) Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells
• Metabolism


  The sum of all the reactions in a cell or the body
• Aspects of metabolism


  • Conversion of glucose to starch, glycogen and cellulose
  • Formation of lipid molecules from glycerol and fatty acids
  • Use of glucose and nitrate ions to form amino acids for protein synthesis
  • Respiration
  • Breakdown of excess proteins to form urea for excretion