1. Microbes are tiny living organisms that can only be seen with a microscope and include bacteria, viruses, fungi, protozoa, and algae. 2. Microbes are classified into different kingdoms based on their structure and characteristics, with the main divisions being prokaryotes and eukaryotes. 3. Bacteria are single-celled microbes that come in different shapes and sizes and are further classified based on their morphology, biochemical traits, staining properties, and antigens.