Actinobacteria sp. are organisms called chemoorganohetereotrophs. They do not use oxygen to breathe. They break down organic material and convert it to inorganic material. Which part of the carbon cycle does this describe?

Decomposition is the breakdown of organic material into simpler inorganic substances. Actinobacteria perform that role in the carbon cycle, so the correct choice is decomposition. Respiration releases carbon dioxide from organisms, while assimilation and photosynthesis involve taking up carbon, not breaking down dead organic matter.

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