Statement I : Bacteria are the sole members of the Kingdom Monera. They are the most abundant microorganisms that occur almost everywhere.
Statement II : The bacterial structure is very simple, they are very complex in behaviour as a group show the most extensive metabolic diversity. 

Statement I is true. Bacteria constitute the Kingdom Monera, which is one of the five kingdoms used in biological classification. Bacteria are indeed the most abundant microorganisms on Earth, and they can be found in a wide range of habitats, including soil, water, the human body, and extreme environments.

Statement II is also accurate. Bacteria are characterized by their simple cellular structure, lacking membrane-bound organelles and a true nucleus. However, despite their structural simplicity, bacteria exhibit a remarkable diversity in their metabolic capabilities and behaviors. They are involved in various ecological processes, including nutrient cycling, decomposition, nitrogen fixation, and pathogenesis. Their metabolic diversity allows them to occupy a wide range of ecological niches and carry out essential roles in ecosystems.