Fossil fuel also represent a reservoir of carbon. Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. According to one estimate, 4 × 1013 kg of carbon is fixed annually in the biosphere through photosynthesis. A considerable amount of carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers. Decomposers also contribute substantially to CO2 pool by their processing of waste materials and dead organic matter of land or oceans. Some amount of the fixed carbon is lost to sediments and removed from circulation. Burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity are additional sources for releasing CO2 in the atmosphere.
The role of bacteria in the carbon cycle is :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Breakdown of organic compounds
Option (1) Breakdown of organic compounds — Correct. As the passage says, decomposers process waste and dead organic matter and return CO2 to the atmosphere.
Option (2) Chemosynthesis — Incorrect. Only a few special bacteria fix carbon this way; it is not the role the passage gives them.
Option (3) Photosynthesis — Incorrect. Carbon is fixed mainly by green plants and phytoplankton.
Option (4) Assimilation of nitrogen compounds — Incorrect. Taking up nitrogen compounds is a step of the nitrogen cycle; it does not move carbon. In the carbon cycle the role of decomposers is to process waste and dead organic matter and return CO2 to the atmosphere.
Note: This passage is taken from NCERT as it is.