Who discovered significant differences between organisms originally categorized under the monera kingdom; thus, these organisms were placed into two separate domains ?

Answer : The correct answer is-

Carl Woese.

The two separate groups for the organisms that originally belonged to kingdom Monera are- Archaea and Bacteria.

Carl Woese proposed three domain classification system according to which life forms can be categorised into three distinct domains, which are-

1) Archaea- having primitive forms of  prokaryotic organisms that live under extremely harsh environmental conditions (like hotsprings, volcanic eruptions).

They have different biochemical composition in their cell wall structure that enables them survive under such conditions.

2) Bacteria- having groups of prokaryotic organism living under moderate climatic conditions.

3) Eukarya- includes eukaryotes (that is organisms with well defined nucleus and membrane bound subcellular organelles).

Thus, he recognised significant differences between organisms originally categorized under the Monera kingdom, and the organism were placed under two different groups that are Archaea and Bacteria.