Question

Explain the different ways in which glucose is broken down in absence of oxygen

Answer 1

Diverse organisms do this indifferent ways – some use oxygen to break-down glucose completelyinto carbon dioxide and water, some use other pathways that do notinvolve oxygen (Fig. 6.8). In all cases, the first step is the break-down ofglucose, a six-carbon molecule, into a three-carbon molecule calledpyruvate. This process takes place in the cytoplasm. Further, thepyruvate may be converted into ethanol and carbon dioxide. This processtakes place in yeast during fermentation. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration. Breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than in the anaerobic process. Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

 

The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP is broken down giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell

Answer 2

anaerobic fermentation or respiration :- Lactic acid is the end product of anaerobic respiration in bacteria and in animals while as ethanol is the end product of anaerobic respiration in fungi like yeast.