Topic 5: Energy Transfers: Anaerobic respiration

Differences in respiration:

• some steps of aerobic respiration occurs within the mitochondria, while anaerobic respiration only occurs in the cytoplasm

• only aerobic respiration includes the link reaction, the Krebs cycle and oxidative phosphorylation

• aerobic respiration yields approximately 34 ATP per glucose molecule, while anaerobic respiration yields only 2 ATP per glucose molecule

In aerobic conditions, which are those without oxygen, cells can produce a small yield of ATP through glycolysis. This can only continue if the reduced NAD that is produced can be oxidised again

The link reaction and Krebs cycle cannot continue if all the NAD and FAD are reduce, because they cannot accept any more protons and electrons. Oxidative phosphorylation cannot occur without oxygen as the final electron acceptor

Two ways in which cells can undergo anaerobic respiration:

1. Alcohol fermentation

2. Lactate fermenation

Alcohol fermentation

• occurs in yeast and some plants

• pyruvate loses a molecule of carbon dioxide and accepts a hydrogen from reduced NAD

• this produces ethanol, and regenerates NAD

• in yeast, it can be used to produce ethanol for wine and beer production

Lactate fermentation

• occurs in some animals and bacteria

• pyruvate accepts a hydrogen from reduced NAD

• this produces lactate and regenerates NAD

• lactate is removed by the blood to be taken to the liver to be converted to glycogen, or oxidised to regenerate pyruvate when oxygen is available

If too much aerobic respiration occurs in muscle tissue, the reduced quantity of ATP produced is insufficient to maintain vital processes for extended time periods

This means lactate accumulates causing cramp and muscle fatigue, and it is also reduces the pH affecting enzymes

Aerobic advantages

• higher yield

• less toxic products

Anaerobic respiration

faster

Aerobic Disadvantages

• longer process

• requires oxygen (need system to acquire it)

Anaerobic Disadvantages

• lower yield (incomplete breakdown of glucose)

• toxic product means unstainable in animals

What happens to lactate? (The Cori Cycle)

1. Lactate taken to liver and kidneys

2. Some lactate converted back to pyruvate →back into aerobic respiration (link reaction)

3. Some lactate converted back into glucose into glucose (gluconeogenesis)

Respiration experiments (Limewater)

• yeast can do both aerobic and anaerobic respiration

• oil layer stops the oxygen getting to the yeast (prevents aerobic respiration)

• if respiring anaerobically there would be a pressure increase in the tube and carbon dioxide bubbles out

• if aerobically there’s no pressure change and lime water does not go cloudy

Respiration practical (conical flask)

• Rate of carbon dioxide production: distance travelled, time and cross sectional for tube

• When in water bath: get it to temperature then put clip, otherwise would increase pressure

• Carbon dioxide causes an increase in pressure and forces the stained water droplet further

Respiration experiments (Manometer)

• aerobic respiration

• carbon dioxide produced is absorbed so no change in volume/pressure in tubes

• soda lime in control tube absorb the carbon dioxide in the air of the tube

• control shows that the volume changes are due to germinating seeds

• syringe is used to restart the experiment - forces red liquid to starting position

• Volume of gas in tube with germinating seeds decrease, pressure in tube decreases, therefore red liquids move towards experimental tube (as lower pressure in that tube than control tube)