Bioenergetics

• Photosynthesis


  An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light
• Photosynthesis equation

  Carbon Dioxide + Water —> Glucose + Oxygen
• Limiting factor

  A condition, that when in shortage, slows down the rate of a reaction
• CO₂ concentration increases


  Rate of photosynthesis increases until a certain point
• CO₂ concentration is high

  Rate of photosynthesis levels off as enzymes become saturated
• Light intensity increases


  Rate of photosynthesis increases until a certain point

  
• Light intensity is high

  Rate of photosynthesis levels off as maximum light has been trapped

  
• Temperature increases


  Rate of photosynthesis increases until optimum temperature

  
• Temperature is high


  Rate of photosynthesis falls as enzymes denature

  
• Chlorophyll


  Can act as a limiting factor for photosynthesis as it allows more light to be trapped
• Inverse proportion describes a relationship between two factors which involves one increasing whilst one decreasing
• Light intensity is inversely proportional to the square of the distance from the light source
• Limiting factors interact and any one of them may limit the rate of photosynthesis
• Limiting factors are important in the economics of enhancing conditions in greenhouses to maximise photosynthesis while maintaining profit
• Uses of glucose produced in 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
• Cellular respiration


  An exothermic reaction which is continuously occurring in living cells to supply energy for living processes
• Organisms need energy for


  • Chemical reactions to build larger molecules
  • Movement
  • Keeping warm
• Aerobic respiration

  Uses oxygen and yields the most energy, occurring mainly in the mitochondria
• Aerobic respiration equation


  Glucose + Oxygen —> Carbon Dioxide + Water
• Anaerobic respiration


  Occurs when there is not enough oxygen, does not yield as much energy, used as a last resort
• Anaerobic respiration in animals


  Glucose —> Lactic Acid
• Anaerobic respiration in plants and yeast (fermentation)


  Glucose —> Ethanol + Carbon Dioxide
• Anaerobic respiration in yeast cells (fermentation) has economic importance in the manufacture of bread and alcoholic drinks
• During exercise

  Heart rate, breathing rate and breath volume increase to supply muscles with more oxygenated blood
• Insufficient oxygen during exercise


  Anaerobic respiration takes place in muscles, causing a build up of lactic acid and an oxygen debt
• Prolonged vigorous activity

  Muscles become fatigued and stop contracting efficiently
• Lactic acid in muscles

  Transported to the liver and converted back into glucose
• Oxygen debt


  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, using the energy transferred by respiration
• Examples of metabolic processes

  • Glucose molecules being converted to starch, glycogen and cellulose
  • A glycerol molecule and three molecules of fatty acids forming a lipid molecule
  • Glucose and nitrate ions forming amino acids, which are used to form proteins
  • The reactions in respiration
  • Urea forming from the breakdown of proteins for excretion