1. Cell Structure:
* Prokaryotes: Lack a nucleus and other membrane-bound organelles. They include:
* Bacteria: Single-celled organisms with diverse shapes and metabolisms.
* Archaea: Similar to bacteria but have unique biochemical features and often thrive in extreme environments.
* Eukaryotes: Possess a nucleus and other membrane-bound organelles. They include:
* Fungi: Heterotrophic organisms that obtain nutrients by absorbing organic matter.
* Protozoa: Single-celled organisms that can be free-living or parasitic.
* Algae: Photosynthetic organisms that can be single-celled or multicellular.
* Helminths: Parasitic worms that are macroscopic but often classified with microorganisms due to their microscopic larval stages.
2. Metabolism:
* Photoautotrophs: Use light energy to synthesize organic molecules from inorganic sources.
* Chemoautotrophs: Use energy from chemical reactions to synthesize organic molecules.
* Photoheterotrophs: Use light energy but obtain organic molecules from external sources.
* Chemoheterotrophs: Obtain energy and organic molecules from external sources.
3. Morphology:
* Shape: Bacteria can be spherical (cocci), rod-shaped (bacilli), spiral (spirilla), or other shapes.
* Size: Microorganisms vary in size, from microscopic viruses to larger protozoa.
* Structure: Presence of features like flagella, pili, capsules, or spores.
4. Genetic Analysis:
* DNA Sequencing: Comparing genetic sequences to determine evolutionary relationships.
* Phylogenetic Analysis: Constructing evolutionary trees based on genetic data.
5. Biochemical Characteristics:
* Enzymatic Activities: Presence or absence of specific enzymes.
* Nutritional Requirements: Dependence on certain nutrients or growth factors.
6. Ecological Roles:
* Decomposers: Break down organic matter.
* Producers: Primary producers in ecosystems.
* Symbionts: Live in close association with other organisms.
* Pathogens: Cause disease.
7. Viruses:
* Viruses are not classified as living organisms, because they lack the ability to reproduce independently. Instead, they are classified based on:
* Type of nucleic acid: DNA or RNA.
* Structure: Shape, size, and presence of envelopes.
* Host range: The organisms they can infect.
Taxonomy:
The classification of microorganisms is organized into a hierarchical system using taxonomic ranks:
* Domain (e.g., Bacteria, Archaea, Eukarya)
* Kingdom
* Phylum
* Class
* Order
* Family
* Genus
* Species
This system allows for the organization and identification of microorganisms, facilitating research and understanding their diversity and importance.
