Respiration could be defined as a metabolic biochemical process that takes place in all living cells of an organism where they produce energy by intake of oxygen and liberation of carbon dioxide from the oxidation of various organic substances. The energy produced is in the form of Adenosine-triphosphate or ATP which is also known as the energy molecule.

Two types of respiration processes have been observed

1. Aerobic respiration 

2. Anaerobic respiration

Aerobic Respiration

Aerobic respiration is a type of cellular respiration that takes place in the presence of oxygen and produces energy. It is observed in both plants and animals and the end product of this type of respiration is water and Carbon dioxide (CO₂).

Have a look at the reaction which takes place during aerobic respiration.

Glucose (C₆H₁₂O₆)  + Oxygen 6(O₂) → Carbon-dioxide 6(CO₂)  +  Water 6 (H₂O) + Energy (ATP)

As observed, in this type of respiration, Glucose molecules are split in the presence of oxygen and the end or by-products which are released are CO_2, water and energy in the form of ATP. The total energy released in this reaction is 2900KJ which is used to produce ATP molecules. It is observed in all types of multicellular organisms. 

Anaerobic Respiration

Anaerobic respiration is another type of cellular respiration that takes place in the absence of oxygen and produces energy. In this process,  glucose breaks down without the help of oxygen and the by-products produced are alcohol, CO₂ and energy or ATP. The process takes place in the cytoplasm of a cell. The chemical reaction of this process is as follows:

Glucose(C₆H₁₂O₆) → Alcohol 2(C₂H₅O H) + Carbon dioxide 2(CO₂) + Energy (ATP )

Aerobic respiration could be divided into 

1. Lactic acid fermentation

2. Alcoholic fermentation