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Question

Yeast can convert glucose into


A

Starch

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B

Alcohol

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C

Lactic acid

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D

Yogurt

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Solution

The correct option is B

Alcohol


Explanation for the correct option

(B) Alcohol

  • Yeasts are facultative anaerobes or obligate aerobes
  • In presence of oxygen, it carries out cellular respiration of carbohydrate source to give CO2 and H2O
  • Yeast undergoes fermentation to give alcohol and CO2
  • The glucose is used as a substrate which gives pyruvate which further undergoes reductive decarboxylation in absence of oxygen with the help of specific enzymes to give ethanol and CO2.
  • The reaction is as follows:-
  • C6H12O2CO2+2C2H5OH

Explanation for incorrect options

(A) Starch

  • Starch is the polymer of glucose formed by multiple glucose monomers.
  • It is mainly produced by plants and algae as a reserve source of carbohydrates.
  • Yeast ferments glucose to give ethanol and CO2 and stores glucose as glycogen.
  • Thus, yeast does not convert glucose to starch.

(C) Lactic acid:

  • Lactic acid is produced by homo and hetero fermenting bacteria
  • The lactic acid-producing bacteria have the enzyme lactic acid dehydrogenase which is responsible for reducing pyruvate (obtained via glucose metabolism) to lactic acid.
  • Yeasts lack this enzyme thus, yeast does not convert glucose to lactic acid.

(D) Yogurt:

  • Yogurt is the product of milk fermentation reaction done with the help of lactose fermenting bacterial cultures.
  • In this lactose is the milk is fermented to give yogurt which is not feasible in yeast cultures.
  • Yeasts do not ferment glucose to give yogurt but play important role in its spoilage.

Hence, the correct option is (B). Yeast can convert glucose into alcohol.


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