Question

Carbohydrates, proteins, fats and organic acids are the various respiratory substrates. Amongst these which is the most preferred substrate for respiration?

• A. Carbohydrates
• B. Proteins
• C. Organic acid
• D. Fats

Answer 1

The correct option is A Carbohydrates

The breaking of the $C-C$ bonds of complex compounds through oxidation within the cells, leading to release of a considerable amount of energy is called respiration.

Respiratory substrates are those organic compounds which are oxidised during respiration to liberate energy inside the living cells. The various respiratory substrates are carbohydrates, proteins, fats and organic acids. Carbohydrates are the most preferred respiratory substrates because they enter the respiratory pathway directly and are easily metabolised.

Fats and proteins cannot be directly used in respiration. Instead they are first broken down to intermediates common to carbohydrate oxidation. Fats are used as respiratory substrates by a number of organisms because they contain more energy as compared to carbohydrates. Proteins are used in respiration very rarely. Only when the body is starving, protein is used as a respiratory substrate. Proteins are hydrolysed to form amino acids from which organic acids are produced. Organic acids enter the Krebs cycle.