Topic 4 - Bioenergetics

• Photosynthesis

  The process by which plants make glucose from sunlight. An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
• The equation for photosynthesis

  light

  Carbon dioxide + water ➔ glucose + oxygen
• Factors which effect the rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• Temperature and rate of photosynthesis

  Increase in temperature increases the rate of photosynthesis:

  • The reaction is controlled by enzymes
  • As the temperature increases to the optimum the rate of reaction increases
  • If the temperature goes higher than the optimum then the enzyme will start to denature and so the rate of reaction decreases
• Light intensity and rate of photosynthesis

  The higher light intensity the higher the rate of the reaction
• Carbon dioxide concentration and photosynthesis

  The higher the concentration the higher the rate:

  • Carbon dioxide is needed to make glucose
  • Therefore the higher the concentration - the more carbon dioxide and the faster the rate.
• Amount of chlorophyll and photosynthesis

  • Chlorophyll converts light energy to food for the plant.
  • Therefore if the levels of chlorophyll are reduced then the rate is also decreased.
• Respiration

  A reaction which occurs in every cell that is the process of transferring energy. An exothermic reaction since energy is transferred to the environment
• Aerobic respiration

  • With oxygen
  • This transfers the most energy
  • Most reactions that make up aerobic respiration take place in the mitochondria
  • Glucose + Oxygen ➔ Carbon dioxide + water
• Anaerobic respiration

  • Without oxygen
  • It doesn't transfer as much energy as aerobic
  • Only used as a last resort
  • Used in yeast cells (fermentation) to make bread and alcoholic drinks
• equation of anaerobic respiration in animals

  Glucose ➔ lactic acid
• equation of anaerobic respiration in yeast cells (fermentation)


  Glucose ➔ ethanol + carbon dioxide
• Organisms need energy for:

  • Chemical reactions to build larger molecules
  • movement
  • keeping warm
• Exercise

  During exercise the human body reacts to the increased demand for oxygen by:

  • Heart rate increasing
  • Breathing rate increasing
  • Breath volume increasing

  This supplies the muscles with more oxygenated blood.
• Insufficient oxygen

  • If insufficient oxygen is supplied anaerobic respiration takes place in muscles.
  • The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt.
  • During long periods of vigorous activity muscles become fatigued and stop contracting efficiently.
• Oxygen debt

  The amount of extra oxygen the body needs after exercising to react with the lactic acid to remove it from cells.

  Blood flowing through the muscles transports lactic acid to the liver where it is converted back to glucose.
• Metabolism


  The sum of all reactions in a cell or body
• Metabolic reactions:

  • Conversion of glucose to starch, glycogen and cellulose
  • The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids
  • The use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
  • Respiration
  • Breakdown of excess proteins to form urea for excretion.
• respiration and metabolism

  The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism.