Chapter 11: Respiration – The release of energy

Chapter 11: Respiration – The release of energy

  • Each cell in every organism needs energy to perform normal life functions
  • Energy is obtained in the metabolic breakdown process
  • Metabolic process is where organic compounds are broken down gradually to release energy
  • This series of reactions are known as cellular respiration (occurs in all living cells)
  • Oxygen is needed together with the organic molecule. Process also produces water and carbon dioxide as waste products
  • Plant cells must also respire to provide for their energy needs
  • Plant cells can convert radiant energy into chemical potential energy
  • Plant cells have lower respiration tempo than animal cells, because their energy needs are less
  • ATP is regarded as energy ‘currency’
  • All living cells energy is temporarily stored in ATP
  • Energy in the cell is locked into ATP to be released when needed
  • ATP is remarkable molecule (nucleotide); consisting of 3 main components
  • 1) Adenine –found in DNA – 2) Ribose –5C sugar– 3) Three phosphate –phosphorus with oxygen –
  • During cellular respiration ATP is formed from ADP/ free phosphate. Using the energy that is released to form the bond
  • ‘Extra’ energy can be stored for a while
  • Cell needs energy for any cell activity
  • ATP releases the energy to become ADP and a free phosphate
  • Forming of AMP occurs only under extreme conditions


Cellular respiration can be compared to combustion: 

  • Both processes need fuel
  • Both need oxygen
  • Both processes release carbon dioxide and water as waste products
  • Both processes release energy


Cellular respiration: 

  • Most eukaryotic and prokaryotic respire aerobically; needs oxygen
  • Organisms can also respire in the absence of oxygen; anaerobic respiration
  • Most cells use aerobic respiration to obtain energy; this is more efficient than anaerobic respiration
  • Aerobic respiration occurs mainly in the mitochondria of the cell; 4 stages can be identified in the process


  • Glycolysis in the cytoplasm
  • Glycolysis does not need oxygen. This stage is anaerobic

  • Forming of Acetyl Co-enzyme A
  • Krebs cycle
  • Process occurs in the mitochondria CO2 is released
  • 2 ATP’s are produced
  • Glucose is now broken down completely
  • Hydrogen transfer system (electron transfer system
  • Process occurs in the mitochondrion
  • Provide 36 (12x3) + 2 from glycolysis = 38 ATP’s


Anaerobic Respiration: 

  • Respiration is the absence of oxygen
  • Can occur in plants and animal cells
  • Many unicellular organisms have the ability to respire anaerobically
  • Animal cells à Lactic acid fermentation
  • Plant cells à Alcohol fermentation
  • Anaerobic respiration uses glucose as fuel, delivers much less energy per reaction
  • When muscles cells experience an oxygen deficiency, a large amounts of pyruvic acid builds up in the cells
  • Having large amounts of pyruvic acid means that the Krebs cycle cannot start because there is not enough oxygen available
  • Pyruvic acid is converted into lactic acid, this remains in the cells
  • Lactic acid can be converted into pyruvic acid, this allows respiration to continue normally
  • Humans can rely only for a few minutes on the ATP released by lactic acid fermentation


Alcohol Fermentation: 

  • Yeast cells respire anaerobically to produce alcohol, CO2 and ATP
  • The type of alcohol that is produced is known as Ethanol
  • Both lactic acid fermentation and alcohol fermentation are not energy effective processes
  • Combustion of glucose is not complete, only two molecules of ATP are produced
  • Anaerobic cells need 20x more fuel per second as an aerobic cell
  • Muscle store so much glucose as glycogen; the cells can respire anaerobically for short periods