Study the image of a biogas plant given below and answer the questions that follow:


Arrange the given steps of biogas production in the correct order.

I - Action of fermentative microbes on monomeric units of complex organic compounds
II - Action of methanogens on organic acids to produce methane and carbon dioxide
III - Action of facultative anaerobic decomposers on organic compounds such as cellulose, proteins, fats, etc.
[1 mark]

The correct option is A III → I → II
Biogas is a methane rich fuel gas, produced by the anaerobic breakdown or digestion with the help of methanogenic bacteria.

Biogas is produced in biogas plants where organic wastes obtained from agricultural farms, sewage treatment plants, etc., are fed into a concrete tank known as a digester. Different types of microbes act upon these wastes and break them down in steps to ultimately release the biogas.

The complex organic compounds (polymers) in the wastes such as cellulose, proteins, etc., are first broken down (hydrolysis) by facultative anaerobic decomposers to their simplest units or monomers.

These monomers are further fermented or anaerobically broken down by decomposers to form organic acids (acidogenesis). Acetogenesis is one of the substeps of acidogenesis in which the monomeric carbohydrates are converted to acetic acid which can act as a substrate for methane production.

Finally, all the end products are reduced by methanogens to produce a mixture of carbon dioxide and methane which is known as biogas. Thus option a is correct.