With reference to the microorganisms involved in production, identify…

The correct answer is Option (3) → Lactic acid - energy source

NCERT groups the products of microbes in three settings: household products (curd, bread, idli dough), industrial products (beverages, antibiotics, organic acids, enzymes) and energy (biogas from sewage and cattle dung).

Option (1) Bread - house hold product — A correct combination. Bread dough is fermented at home and in bakeries by baker’s yeast, Saccharomyces cerevisiae.

Option (2) Penicillin - antibiotic — A correct combination. Penicillin, made by the fungus Penicillium notatum, was the first antibiotic to be discovered.

Option (3) Lactic acid - energy source — The odd combination. Lactic acid is not a fuel. Lactobacillus produces lactic acid as an industrial product; at home the same lactic acid bacteria (LAB) turn milk into curd.

Option (4) Biogas - energy source — A correct combination. Methanogens such as Methanobacterium give out mainly methane, which is burnt as fuel.

Note: The original NTA paper printed Option (3) as ‘Lactic acid - industrial product’. As per NCERT that pairing is also correct, because Lactobacillus produces lactic acid industrially, so no option was odd. For the benefit of students and to ensure a single answer, Option (3) has been changed to ‘Lactic acid - energy source’.

NCERT Extract:
Chemicals, Enzymes and Other Bioactive Molecules – “… Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.”