Explain the three pathways of breakdown in living organisms.

Explanation

The food material taken inside the body is further processed in cells to generate energy for various life processes. Different organisms perform various pathways for the breakdown of glucose into water and energy completely. Depending upon the condition of oxygen present or absent during the reaction, the end products vary from organism to organism. However, in all the cases, the first step lies in common with the breakdown of 6 carbon molecule glucose to that of the 3 carbon molecule known as pyruvate. Also, the energy released in aerobic condition is much more than that of the energy produced under anaerobic conditions. `"Glucose" to "Pyruvate" + "Energy"`
Further, if this process takes place in cytoplasm i.e. anaerobic conditions, pyruvate is then converted to ethanol and carbon dioxide. Similarly, if the reaction occurs inside mitochondria i.e. aerobic conditions converts the pyruvate into carbon dioxide, water and energy.
(i) Aerobic conditions are prevalent in the presence of oxygen. In mitochondria, majorly such reactions are found where oxygen is available in abundance to convert the pyruvate into water, energy and `CO_2`

(ii) Anaerobic conditions can occur in two cases :
(a) Oxygen deficient condition present in cytoplasm produces ethyl alcohol, energy and carbon dioxide. Such products are also released by yeast during the process of fermentation.
(b) Lack of oxygen is observed in some cases due to excessive exercise when the oxygen content in muscle cells is used up completely. In such cases, lactic acid is produced along with the energy as a by-product.