Question

In Yeast, anaerobic respiration produces
a. $CO_2$ and ethanol
b. $CO_2$ and water
c. $O_2$ and lactic acid
d. $O_2$ and pyruvic acid

Answer 1

Respiration is an exergonic and catabolic-physio-chemical process that involves the exchange of environmental oxygen and body carbon dioxide through a liquid medium and the oxidation of glucose inside the mitochondria to produce energy which is partly stored in the high energy bonds of ATP molecules.

Complete answer:
- Anaerobic respiration or fermentation involves the production of energy from the food nutrients in the absence of oxygen.
- It involves glycolysis in which one molecule of glucose is degraded into two molecules of pyruvic acid, two ATP molecules and two $NADPH_2$ molecules. Pyruvic acid acts as an H-acceptor. Depending upon the metabolic pathways the end-product of anaerobic respiration is either ethanol and carbon dioxide as in yeasts or lactic acid as in some bacteria and muscles in the human body.
- This process is involved in the brewing industry for producing beverages like beer, rum, whiskey, etc. It is done by brewing – yeast. It is also used in the baking industry in which carbon dioxide produced causes doughing of wheat flour.
- Besides this, a number of other products are formed by the fermentation of molasses caused by yeasts like glycerol, acetic acid, lactic acid, phenyl ethanol, amyl alcohol, etc. The product produced depends upon the nutrient medium.

Hence, the correct answer is option (A).

Note: Advantages of fermentation are:
- It helps in retting of stem fibres and cleaning of hides to make leathers.
- It is also employed in curing tea and tobacco leaves.
- It supplements the aerobic respiration.
- Production of vinegar by acetic acid bacteria.
- Synthesis of organic acid like acetic acid and citric acid.