Cellular Respiration & its types:


CELLULAR RESPIRATION:

 In biological systems oxidation-reduction is a chemical reaction usually involves the removal of hydrogen atom from one molecule and the gain of hydrogen atom by another molecule. Cellular respiration is a series of complex oxidation-reduction reactions by which living cells obtain energy through the breakdown of organic matter.






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KINDS OF CELLULAR RESPIRATION:

There are two kinds of respirations:

1) Aerobic respiration

2) Anaerobic respiration

Aerobic respiration takes place in the presence of abundant atmospheric oxygen, whereas, anaerobic respiration occurs in the absence of oxygen. The organic molecule that generally undergoes breakdown in cellular respiration in order to release energy is glucose, therefore, glucose is supposed to be respiratory fuel. The initial breakdown of glucose in both aerobic and anaerobic respirations is quite same, in which it is broken down into two molecules of pyruvates.

 This common step of aerobic and anaerobic respirations is called glycolysis. The pyruvates undergo in different respiratory pathways depending upon the availability of oxygen and the kind of organism. If oxygen is available, the further breakdown of pyruvates takes place aerobically and the final products are carbon dioxide and water with the release of large amount of energy i.e., 36 ATPS (in eukaryotes) or 38 ATPs (in prokaryotes). If oxygen is absent, then the pyruvates are broken down anaerobically and the final products are either lactic acid or ethanol and carbon dioxide with release of very small amount of energy i.e., just 2 ATPs.

 MECHANISM OF ANAEROBIC RESPIRATION

Anaerobic respiration takes place in many microorganisms (bacteria, yeast), muscle cells of vertebrates and in the cells of higher plants, Anaerobic respiration is incomplete breakdown of glucose in the absence of oxygen. It is also known as fermentation. There are two pathways of anaerobic respiration depending upon the nature of final products i.e.. lactic acid fermentation and alcoholic fermentation.

 Lactic acid fermentation:

It consists of glycolysis followed by the reduction of pyruvate by NADH to lactic acid. The pathway operates anaerobically because after NADH transfers its electron to the pyruvate, it is "free" to return and pick up more electrons during the earlier reaction of glycolysis.

Lactic acid fermentation occurs in anaerobic bacteria and in the muscles of mammals as well as human during strenuous exercise when oxygen supply is exhausted. The accumulation of lactic acid causes muscles fatigue Le., muscles become unable to contract and begin to ache.

 Alcoholic fermentation:

 Alcoholic fermentation is found in yeast. It consists of glycolysis followed by the decarboxylation of pyruvate to acetaldehyde then reduction of acetaldehyde by NADH to ethyl alcohol or ethanol. This pathway also operates anaerobically because after NADH transfers electron to the acetaldehyde, it is "free" to return and pick up more electrons during the earlier reaction of glycolysis.