The respiration which takes place without using oxygen is called anaerobic respiration.
In other words, when the breakdown of glucose (food) occurs without the use of oxygen, it is called anaerobic respiration.
It is called anaerobic respiration because it takes place without air which contains oxygen (‘anaerobic’ means ‘without air).
The microscopic organisms like yeast (and certain bacteria) obtain energy by anaerobic respiration.
In anaerobic respiration, the micro-organisms like yeast break down glucose (food) in the absence of oxygen to form alcohol and carbon dioxide, and release energy.
The breaking down of glucose (food) during anaerobic respiration carried out by yeast can be represented by writing a word equation as follows