10.2.3 Anaerobic and Aerobic Respiration

• Respiration


  The chemical reactions that break down nutrient molecules in living cells to release energy for metabolism
• Aerobic respiration


  • Needs oxygen
  • Releases a relatively large amount of energy
  • Breakdown of food substances in the presence of oxygen & occurs in mitochondria
• Aerobic respiration


  Glucose + oxygen → carbon dioxide + water
• Respiration is a chemical reaction catalysed by enzymes
• Anaerobic respiration


  • Does not need oxygen
  • Releases a relatively small amount of energy
  • Still requires enzymes & occurs in cytoplasm
• Anaerobic respiration in yeast

  Glucose → ethanol + carbon dioxide
• Bread making with yeast


  The carbon dioxide released makes the bread rise
• Biofuels


  Anaerobic respiration is used to make biofuels, a form of renewable energy due to the ethanol formed
• Making biofuels


  1. Plant material is used as the substrate

  2. It is chopped up and mixed with yeast

  3. The liquid is separated and water is removed, leaving a concentrated solution of ethanol

  4. Sometimes waste parts of crop plants are used, but in other places, crops are grown specifically to be harvested for making ethanol
• In some places, this is causing concern that there is less land available for local people to grow food crops needed for survival
• Measuring rates of respiration in yeast #1


  Measuring the height of foam or dough
• Measuring rates of respiration in yeast #2

  Counting the number of bubbles produced
• Measuring rates of respiration in yeast #3

  1. Measure the volume of gas collected in a set period of time

  2. Inverted gas collection or collect gas in a syringe

  3. Measure volume of gas produced in a certain period of time

  4. Make sure apparatus is airtight
• Measuring rates of respiration in yeast #4

  1. Use hydrogen carbonate indicator

  2. Bicarbonate indicator is purple in low concentrations of carbon dioxide

  3. It turns yellow in high concentrations of carbon dioxide (this would show respiration is happening)