Respiration

• Respiration


  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
• Aerobic respiration


  Respiration that takes place with oxygen
• Anaerobic respiration


  Respiration that takes place without oxygen
• 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 the body of humans

  • 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
• Respiration is a series of chemical reactions that release energy from glucose inside cells
• The respiration reactions are all controlled by enzymes
• Methylene blue


  A coloured indicator that can be used to investigate the effect of temperature on the rate of aerobic respiration in yeast
• Yeast


  • It can respire both aerobically and anaerobically
  • In the experiment, its rate of aerobic respiration is being investigated
• 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
• Variables to control


  • Volume/concentration of dye added
  • Volume/concentration of yeast suspension
  • Concentration of glucose
  • pH
• A buffer solution can be used to control the pH level to ensure that no enzymes are denatured
• 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
• Increasing the temperature above a certain point causes the enzymes involved in respiration to denature; the shape of their active site changes and they can no longer form enzyme-substrate complexes
• Aerobic respiration


  The chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
• Aerobic respiration


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


  1. Glucose → Lactic acid (in animals)

  2. Glucose → Alcohol + Carbon dioxide (in yeast)
• Lactic acid builds up in muscle cells and lowers the pH of the cells (making them more acidic)
• Cells excrete lactic acid into the blood. When blood passes through the liver, lactic acid is taken up into liver cells where it is oxidised, producing carbon dioxide and water
• The waste products of lactic acid oxidation are carbon dioxide and water
• The ONLY product made in anaerobic respiration in animals is lactic acid. Carbon dioxide is NOT one of the products made in anaerobic respiration in animals
• Comparing aerobic and anaerobic respiration

  • Oxygen needed/not needed
  • Glucose breakdown complete/incomplete
  • Products: Carbon dioxide and water/Lactic acid (animals), Carbon dioxide and ethanol (yeast)
  • Energy released: A lot/A little