Anaerobic respiration

• What is meant by an obligate anaerobe?

  Can’t survive in the presence of oxygen
• what is meant by a facultative anaerobe?

  synthesise ATP by aerobic respiration if oxygen is present, but switch to anaerobic when oxygen absent
• what is meant by obligate aerobes?

  organisms which can only synthesise ATP in the presence of oxygen eg mammals
• State what is meant by fermentation

  A form of anaerobic respiration wherein complex organic compounds are broken down into simpler inorganic compounds without the use of oxygen or an electron transport chain
• What are the two types of fermentation and where do they occur?

  • Alcoholic fermentation- yeast and many plants
  • Lactate fermentation- results in the production of lactate and happens in animal cells
• What happens when there's no oxygen at the end of an ETC as a final electron acceptor? (in anaerobic respiration)

  • ATP synthesis by chemiosmosis stops
  • As the flow of electrons stops
  • reduced NAD and FAD can’t be oxidised as there's nowhere for the electrons to go
  • NAD and FAD can’t be regenerated so decarboxylation and oxidation comes to a stop
  • krebs cycle comes to a stop
  • as there are no coenzymes to accept hydrogens being removed
  • glycolysis would also stop if it were not for fermentation
• What are the products of alcoholic fermentation?

  • Ethanol
  • Carbon dioxide
• How does lactate fermentation happen in mammals?

  • pyruvate can act as a hydrogen acceptor, accepting a H from reduced NAD to form lactate catalysed by the enzyme lactate dehydrogenase
  • NAD is regenerated
  • Can be used to keep glycolysis happening so a small quantity of ATP is still produced
• Why do we breathe heavily after exercise and why do we have oxygen debt?

  • Lactate needs to be converted back to glucose in the liver
  • Oxygen is needed to complete this process
• why can lactate fermentation not happen indefinitely or continuously?

  • reduced quantity of ATP produced not enough to mmaintain vital processes for a long period of time
  • Accumulation of lactic acid causes a fall in pH leading to denatured proteins. Respiratory enzymes and muscle filaments are made from proteins and will cease to function at low pH
• How is lactic acid removed from muscles and taken to the liver?

  Through the bloodstream
• how can physical fitness be improved?

  • increase blood supply and flow
  • increases the rate of lactic acid removal
  • by allowing intensity and duration of exercise to increase
• is alcoholic fermentation reversible or irreversible?

  • irreversible
  • lactate fermentation is reversible
• what eventually happens to lactic acid in anaerobic respiration?

  Removed from the muscles and taken to the liver via the bloodstream
• What happens in alcoholic fermentation?

  • Pyruvate converted to ethanal
  • By the enzyme pyruvate decarboxylase
  • Ethanal accepts a hydrogen atom from reduced NAD, becoming ethanol
  • Regenerated NAD can continue to act as a coenzyme and glycolysis can continue
• True or false? Anaerobic respiration is a short term process and can continue indefinitely in the absence of oxygen?

  False- it’s NOT a short term process and continues indefinitely in the absence of oxygen
• why is accumulation of ethanol in yeast cells dangerous?

  • toxic
  • if it accumulates above 15% the yeast won’t survive
• Using your knowledge of aerobic and anaerobic respiration, explain why overwatering can kill plants. (PPQ)

  • (No oxygen so) no aerobic respiration occurs
  • No, link reaction / Kreb’s cycle / ETC / oxidative phosphorylation
  • No oxygen to act as the final, electron acceptor
  • (Plant has to) switch to anaerobic respiration
  • So glycolysis occurs
  • Alcoholic fermentation occurs
  • Pyruvate to ethanal to ethanol
  • Named enzyme e.g. pyruvate decarboxylase
  • (Only) 2 ATP produced
  • ethanol is toxic
  • (alcoholic fermentation) is irreversible
  • Less ATP produced
  • Less active transport
• true or false? almost all obligate anaerobes are prokaryotes

  TRUE
• true or false? in anaerobic respiration, organic substances are completely broken down

  FALSE- not broken down completely, ATP can only be synthesised by substrate level phosphorylation