The process of respiration is of two types based of the presence and absence of oxygen. They are
  1. Aerobic respiration
  2. Anaerobic respiration  
Aerobic respiration
The process of respiration in which the food (carbohydrates or glucose) we eat is broken down into carbon dioxide and water in the presence of oxygen is known as aerobic respiration.
Glucose inthepresenceofoxygen carbon dioxide + water + energy.
In this mode of respiration, a high amount of energy is released in the living organisms. Human beings and most of the animals undergo aerobic respiration.
Anaerobic respiration
The process of respiration in that occurs in the absence of oxygen is known as anaerobic respiration.
The organisms in which this mode of respiration is observed are known as anaerobes. Yeasts are single-celled organisms that undergo anaerobic respiration and are hence known as anaerobes.
During anaerobic respiration, the food (glucose) consumed by the anaerobes is broken down to alcohol and carbon dioxide as represented below.
Glucose intheabsenceofoxygen alcohol + carbon dioxide + energy.
As yeasts produce alcohol during their respiration they are used in the manufacture of wine and beer.
Anaerobic respiration in humans:
The process of anaerobic respiration is also seen in the cells of our muscles when oxygen is deficient. This condition comes into action at the time of heavy exercise, prolonged fasting, cycling, walking for many hours where the demand of energy is very high.
During this lactic acid is produced from glucose in the muscle cells.
Glucose intheabsenceofoxygen lactic acid + energy
Muscle cramps
It is a condition that indicates the process of anaerobic respiration. It is due to the production of lactic acid from glucose during anaerobic respiration. To get rid of this condition, a hot water bath or massage is given. This is because hot water bath or massage improves the circulation of blood which increases the supply of oxygen, making the muscle cells to respire aerobically, preventing the formation of lactic acid.