Question

During lactic acid fermentation
A. ${O_2}$ is used, $C{O_2}$is not liberated.
B. ${O_2}$ is not used, $C{O_2}$ is liberated.
C. ${O_2}$ is used, $C{O_2}$ is liberated.
D. Neither ${O_2}$ is used, nor $C{O_2}$ is liberated.

Answer 1

Hint:- The mechanism of reduction of pyruvate into lactic acid is called lactic acid fermentation. Incomplete oxidation of glucose takes place in lactic acid fermentation. Glycolysis is the pathway which converts glucose into pyruvate molecules. One Glucose molecule is converted into pyruvate in a single glycolysis pathway. This pyruvate is converted into lactic acid in some anaerobic bacteria and in some skeletal muscles of animals.

Complete answer:
Lactic acid fermentation is an anaerobic process which does not require oxygen. In anaerobic organisms, this occurs as they can out withstand oxygen. In aerobic organisms, lactic acid fermentation happens whenever the cells utilize oxygen faster than can be supplied by the circulatory system.
Glycolysis is the principal pathway for ATP synthesis. One $NA{D^ + }$is reduced to NADH during glycolysis. This NADH is oxidized to $NA{D^ + }$by oxygen in aerobic pathways. But in anaerobic conditions, oxygen is absent and $NA{D^ + }$is regenerated by transferring electrons from NADH to form a reduced end product called lactate or lactic acid. No oxygen is used for this process and the only product formed is lactate. Carbon dioxide liberation does not take place.
The reduction of pyruvate into lactic acid is catalysed by the enzyme lactate dehydrogenase (LDH). The glycolytic sequence of conversion of pyruvate into lactate in muscle cells is called muscle glycolysis which is an example of anaerobic glycolysis. Lactic acid fermentation is important commercially because the production of cheese yoghurt and other dairy products depends on the microbial fermentation of lactose which is the main sugar found in milk.

So, the complete answer is Option D.

Note:- Besides lactic acid fermentation, alcohol fermentation takes place in anaerobic organisms such as yeast. In alcohol fermentation, pyruvate undergoes decarboxylation and is converted into acetaldehyde by releasing carbon dioxide. Acetaldehyde then undergoes dehydrogenation by converting NADH into $NA{D^ + }$to form ethyl alcohol or ethanol by an enzyme called alcohol dehydrogenase.