Respiration

• Respiration is a chemical process that involves the breakdown of nutrient molecules (specifically glucose) in order to release the energy stored within the bonds of these molecules
• Respiration is enzyme-controlled
• Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically)
• Much less energy is released for each glucose molecule broken down anaerobically compared to the energy released when it is broken down aerobically
• Respiration occurs in all living cells; most of the chemical reactions in aerobic respiration take place in the mitochondria
• Uses of energy in living organisms

  • Muscle contraction
  • Protein synthesis
  • Cell division (to make new cells)
  • Growth
  • Active transport across cell membranes
  • Generation of nerve impulses
  • Maintaining a constant internal body temperature
• The energy released during respiration is used to fuel many processes in the human body
• The respiration reactions are all controlled by enzymes
• Respiration


  A series of chemical reactions that release energy from glucose inside cells
• Energy is released during respiration, it is NEVER made, produced, or created
• Investigating the effect of temperature on the respiration of yeast cells

  1. Add methylene blue dye to a suspension of living yeast cells

  2. Measure the time taken for the methylene blue to discolour (lose its colour)

  3. The faster the dye changes from blue to colourless, the faster the rate of respiration
• Independent variable


  The variable that is changed on purpose
• Dependent variable


  The variable that is measured, i.e. the variable that depends on the independent variable for its outcome
• It is important to control other variables that might influence the dependent variable
• As the temperature increases up to 40 °C

  The rate of respiration increases so the time taken for the solution to become colourless reduces
• Increasing the temperature above 40 °C

  The rate of respiration decreases so the time taken for the solution to become colourless increases
• Aerobic respiration

  Respiration that requires oxygen and is the complete breakdown of glucose to release a relatively large amount of energy
• Aerobic respiration


  Glucose + Oxygen → Carbon dioxide + Water + Energy
• The balanced chemical equation for aerobic respiration is the same as the photosynthesis equation, only the other way around
• Balanced chemical equation for aerobic respiration

  C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
• Anaerobic respiration


  Respiration that does not require oxygen and is the incomplete breakdown of glucose to release a relatively small amount of energy
• Anaerobic respiration in animals

  Glucose → Lactic acid + Energy
• Anaerobic respiration in yeast

  Glucose → Ethanol + Carbon dioxide + Energy