Unicellular organisms like yeast undergo an alternate pathway of respiration in which an organic substrate is broken down in absence of oxygen. The end products are alcohol and CO2

. Such a process is called alcoholic fermentation. In Yeast, the fermentation products are ethyl alcohol and carbon dioxide.

Fermentation products of Yeast:
Yeast, a type of fungus, undergoes fermentation under anaerobic conditions to produce energy. This process involves the breakdown of glucose into simpler compounds, resulting in the production of various byproducts. The main fermentation product of yeast is ethyl alcohol (ethanol), which is used in the food and beverage industry. Another byproduct of yeast fermentation is carbon dioxide (CO2), which is responsible for the rising of bread dough and the effervescence in beer and champagne.

Explanation of the Correct Answer (Option D - Ethyl alcohol and CO2):
When yeast undergoes fermentation, it produces ethyl alcohol and carbon dioxide as the main byproducts. This process is known as alcoholic fermentation.

Alcoholic Fermentation:
1. Yeast cells break down glucose (a sugar) into pyruvate through a series of enzymatic reactions. This process is called glycolysis.
2. Pyruvate is then converted into acetaldehyde, a toxic compound, by the enzyme pyruvate decarboxylase. This step releases carbon dioxide as a waste product.
3. Acetaldehyde is further reduced to ethyl alcohol (ethanol) by the enzyme alcohol dehydrogenase. This step regenerates the necessary coenzyme NAD+ for glycolysis to continue.

Significance of Ethyl Alcohol and Carbon Dioxide:
1. Ethyl alcohol (ethanol) is a valuable product used in the production of alcoholic beverages such as beer, wine, and spirits. It is also used as a solvent and a fuel source.
2. Carbon dioxide (CO2) is responsible for the leavening effect in baking. It creates bubbles in dough, causing it to rise and become light and fluffy. In the production of beer and champagne, carbon dioxide provides carbonation and gives the beverages their characteristic effervescence.

Other Options:
a) H2O (Water) and CO2: While water (H2O) is a byproduct of cellular respiration, it is not a direct fermentation product of yeast. Therefore, option a is incorrect.
b) Methyl alcohol (methanol) and CO2: Yeast does not naturally produce methyl alcohol during fermentation. Methanol is a toxic substance and is not a desired byproduct. Therefore, option b is incorrect.
c) Methyl alcohol (methanol) and water: As mentioned above, yeast does not produce methyl alcohol during fermentation. Water is a byproduct of cellular respiration but not a direct fermentation product. Therefore, option c is incorrect.