Question

How does anaerobic respiration occur in humans?

Answer 1

Hint: Respiration is the process in which complex substances are broken down in the cells through the oxidation process and carbon dioxide and water are produced. The energy is released in the process which is utilized to fulfil body energy needs and processes. Aerobic and anaerobic respiration is two types of respiration on the basis of the availability of oxygen in the process.

Complete answer:
Glycolysis is the process in which partial oxidation of glucose takes place and pyruvic acid is formed. The fate of the pyruvic acid depends on whether the further breakdown occurs in the presence or absence of oxygen. Hence, glycolysis occurs in all organisms.

In anaerobic respiration, the partial oxidation of glucose takes place which results in the formation of different products. There are two kinds of anaerobic respiration on the basis of the products formed. These are lactic acid fermentation and alcoholic fermentation.

 In lactic acid fermentation, the pyruvic acid that is formed after glycolysis is converted into lactic acid in the presence of lactate dehydrogenase. This type of anaerobic fermentation occurs in bacteria and muscle cells of humans when there is a lack of oxygen. When we do exercise, the lactic acid accumulates in the muscle cells which results in muscle fatigue. Hence, we take deep breathing after running or performing the heavy exercise to fulfil the oxygen need of muscle cells.

During alcoholic fermentation, the pyruvic acid is converted into ethanol and water in the presence of pyruvic acid decarboxylase and alcohol dehydrogenase. It involves a series of reactions. This type of fermentation occurs in yeast.

During anaerobic respiration, a very little amount of energy is released. All of the energy produced is not trapped as high energy ATP bonds. Hence, it occurs only in lower organisms as they do not have many body requirements.

Note: The respiration in which oxygen is completely utilized to produce $CO_2$ and $H_2O$ is called aerobic respiration. It is also called the Krebs cycle. A large number of ATP molecules is synthesized in aerobic respiration. This type of respiration occurs in the mitochondria of eukaryotes.