NEET Biology Respiration In Plants Based Practice Questions & Answers with Viewers Discussion and Detailed Explanation

Answer: (b)

When oxygen is not available (anaerobic condition) yeast and some other microbes convert pyruvic acid into ethyl alcohol. It is a two step process. In the first step pyruvic acid is decarboxylated to yield acetaldehyde and $CO_2$ .

Pyruvic acid is a 3-C compound and acts as electron donor while acetaldehyde is the electron acceptor.

$CH_3 COCOOH →↖{pyruvic}↙{carboxylase} CH_3 CHO + CO_2$

In the  second  step acetaldehyde is  reduced to ethyl  alcohol by NADH 2 formed in the  glycolysis.

$CH_3 CHO + NADH_2 →↖{Alcoholic}↙{dehydrogenase}C_2 H_5 OH + NAD$