Question

Yeast is used in wine and beer industries because it respires:

• A. Aerobically producing oxygen
• B. Aerobically producing alcohol
• C. Anaerobically producing alcohol
• D. Anaerobically producing ${\mathrm{CO}}_2$

Answer 1

The correct option is C

Anaerobically producing alcohol

The explanation for the correct option:

(C ) Anaerobically producing alcohol

• Yeasts are facultative anaerobes or obligate aerobes.
• Yeast undergoes fermentation to give alcohol and${\mathrm{CO}}_2$.
• The glucose is used as a substrate which gives pyruvate (via EMP pathway) which further undergoes reductive decarboxylation in absence of oxygen with the help of specific enzymes to give ethanol and ${\mathrm{CO}}_2$
• As yeasts give alcohol with a little amount of ${\mathrm{CO}}_2$ by anaerobic fermentation, it became an important tool in the production of alcoholic drinks like wine and beer.

The explanation for the incorrect options:

Aerobically producing oxygen

• Yeast undergoes cellular respiration in presence of oxygen (aerobic conditions) to give ${\mathrm{CO}}_2$and${\mathrm{H}}_2\mathrm{O}$.
• Thus it does not respire aerobically to give oxygen.

Aerobically producing alcohol

• Yeast produces alcohol with the liberation of ${\mathrm{CO}}_2$ in absence of oxygen (anaerobically) by the process known as fermentation.
• Thus it does not give alcohol under aerobic conditions instead it gives ${\mathrm{CO}}_2$and ${\mathrm{H}}_2\mathrm{O}$

Anaerobically producing ${\mathrm{CO}}_2$

• Yeast produces ${\mathrm{CO}}_2$ both aerobically and anaerobically
• ${\mathrm{CO}}_2$ is a natural byproduct of the alcohol fermentation procedure but the wine and beer industries require alcohol in its production thus yeast is not used with an intention of producing ${\mathrm{CO}}_2$ but instead used for the alcohol content it produces.
• Hence, options (A), (B), (D) are incorrect.

Hence the correct option is (C). Yeast is used in wine and beer industries because it respires anaerobically producing alcohol.