Answer: B). bacteria
A decomposer is an organism that breaks down the organic materials such as the dead remains of plants and animals into simpler substances, which are either consumed by these decomposers or conducted by the plants for their growth and metabolism. Decomposition is a vital recycling process in every ecosystem.
Bacteria are smallest and most abundant microbes in the soil. The bacteria plays an important role in decomposition of possibly all types of organic matter present in the dead remains. They are responsible for the formation of compost and humus in the soil.
According to the above information, this can be stated that bacteria is the organism which will be most effective in decomposing the leaf tissues, allowing the nutrients and minerals to be recycled in the environment.
