I do believe that it is both naturally occurring and caused by human activity. Although science has proven that it is something that naturally progresses with time, humans have sped up the process. Hope this helps:)
Bacteria: are single-celled microscopic organisms that are characterized by the presence of incipient nucleus and few membrane-less cell organelles.
Fungi: are eukaryotes that are characterized by the presence of chitin in the cell wall.
Cell Type: All bacteria are prokaryotes. All fungi are eukaryotes.
Bacteria, algae, protozoa,
I believe Energy absorbing reactions are endergonic.