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Sometimes animal and plant cells cannot get enough oxygen to carry out aerobic respiration. But they still need to obtain energy to stay alive.
So they use an emergency system of reactions, that is anaerobic respiration.
When you sprint for a bus, your muscles use so much oxygen that you cannot supply it in time. So they cannot use aerobic respiration. Instead they use anaerobic respiration in the following way:
How long could you sprint? Not very far before things get very sore!
This way of getting energy is not as efficient as aerobic respiration and it also leaves a poisonous chemical, lactic acid. This stops your muscles working and they get sore.
When you stop the lactic acid is slowly destroyed but that needs oxygen.The amount of oxygen you need for this is called the 'oxygen debt'.
If the roots of a plant get waterlogged they start to run out of oxygen too. So they need to use a different form of anaerobic respiration. The one they use is this:
It is also the reaction used by yeast cells when they make bread or alcoholic drinks. (Remember that when you answer the question below.)
Again, like lactic acid, ethanol is poisonous - that's why it affects braincells! If there is too much ethanol produced it will kill the cells. So it must be got rid of by using oxygen in aerobic reactions.
Otherwise the plant cells get 'pickled' - permanently!