Bioenergetics

• Photosynthesis is an endothermic reaction as it takes in energy.
• Photosynthesis takes place in the leaves of a plant as leaves contain chlorophyll which absorbs light energy.
• word equation for photosynthesis = water + carbon dioxide → oxygen + glucose

  • carbon dioxide and water are chemically reacted using energy from light which produces glucose and oxygen.
• Uses of glucose made through photosynthesis

  1. Release energy through respiration

  2. Produce the insoluble storage molecule starch

  3. Convert glucose to fats and oils for storage

  4. Make cellulose for cell walls

  5. Produce amino acids for protein synthesis
• Respiration


  Takes place in the mitochondria
• When there is no sunlight for photosynthesis

  The plant can convert starch back to glucose to respire
• Plants need to absorb nitrate ions from the soil to make amino acids from glucose.
• Farmers want to increase the rate of photosynthesis as this increases the yield of crops they produce. To do this, farmers light and heat their greenhouses and add extra carbon dioxide. The extra cost has to be justified by the increase in yield. Some gardeners use oil burners as these release heat and carbon dioxide at the same time.
• Energy is needed for:

  • movement
  • to keep warm
  • chemical reactions to build larger molecules
• The energy we need is supplied by cellular respiration. Respiration is an exothermic reaction because it releases energy and it takes place continually in all living cells.
• word equation for aerobic respiration = glucose + oxygen -> carbon dioxide + water

  • aerobic respiration releases a lot of energy because the glucose molecule has been fully oxidised.
  • symbol for glucose = C6H12O6
• Anaerobic respiration in muscles:

  • Muscle cells need a lot of energy for contraction and under certain conditions the amount of oxygen is limited.
  • When there is a shortage of oxygen, muscle cells can respire anaerobically.
  • During anaerobic respiration in muscles, glucose is converted to lactic acid and anaerobic respiration does not require any oxygen.
  • glucose → lactic acid
• Anaerobic respiration releases much less energy then aerobic respiration because in anaerobic respiration the oxidation of glucose is incomplete
• Anaerobic respiration in plant and yeast cells:

  • glucose → ethanol + carbon dioxide
  • Anaerobic respiration in yeast cells is called fermentation and we use this reaction to make alcoholic drinks (the alcohol is ethanol which is produced by fermentation). When making bread, the carbon dioxide produced by fermentation is useful.
• Aerobic respiration during exercise


  1. Body needs more energy for muscle contraction

  2. Body cells require more oxygen
• Breathing during exercise


  1. Breathing rate increases

  2. Breathing volume increases

  3. Gets more oxygen into the bloodstream
• Heart rate during exercise


  Increases to pump oxygenated blood around the body
• Anaerobic respiration during exercise


  Occurs when not enough oxygen can be supplied to the muscles
• Anaerobic respiration


  Incomplete oxidation of glucose causes a build up of lactic acid
• Lactic acid build up


  Makes the muscles become fatigued during long periods of rigorous activity
• Lactic acid build up


  Causes the muscles to stop contracting efficiently
• Removing lactic acid from muscles


  1. Lactic acid is transported out of the muscles by the blood

  2. Taken to the liver

  3. Converted back to glucose in a series of chemical reactions
• Reacting with the accumulated lactic acid requires oxygen.
• Oxygen debt


  The amount of extra oxygen the body needs after exercise to deal with the accumulated lactic acid
• Energy released by respiration is used by enzymes to synthesise new molecules in the cell.
• Metabolism is the sum of all the chemical reactions in a cell or the body.
• Glucose in humans is converted into glycogen, the storage form of glucose.
• 1 glycerol molecule + 3 fatty acid molecules → lipid
• Humans do not need to eat a large amount of protein so excess proteins are broken down into the chemical urea and urea is then excreted by the kidneys.