Explain the three pathways of breakdown …

The process of taking in oxygen and to use it in the process of break - down of food for cellular needs is called as respiration.

There're three pathways of breakdown of glucose in living organisms. They're as follows:

(i) Aerobic respiration:The process of breaking down of food in the presence of oxygen to form energy is called as aerobic respiration.

The 6 - carbon molecule, glucose is broken down into a 3 - carbon molecule, pyruvate. This all happens in the presence of oxygen. They by - products are Carbon dioxide, Water and Energy.

(ii) Anaerobic respiration: The process of breaking down of food in the absence of oxygen to form energy is called as anaerobic respiration.

During heavy exercise, our body needs more energy to continue our exercise. Here, the more oxygen is needed. But the oxygen taken by nose is insufficient. And there's no time to break down food in the presence of oxygen 'cause of lacking of oxygen.

So, the energy produced in mitochondria in the absence of oxygen produce lactic acid which causes muscle cramps.The pyruvate is again broken down into Lactic acid which's also a three - carbon molecule.

(iii) In mitocondria: The break down of pyruvate using oxygen takes place in mitochondria.

Pyruvate is broken down to give a three - carbon molecules of Carbon dioxide.