Single-celled organisms that lack a nucleus (prokaryotes).
They have various shapes: spherical (cocci), rod-shaped (bacilli), spiral (spirilla), and more.
Bacteria are found everywhere: in soil, water, the human body, and extreme environments like hot springs.
Viruses:
Acellular (non-living) infectious agents made up of a protein coat and genetic material (DNA or RNA).
They can only reproduce inside a host cell, causing diseases such as the flu, HIV, and COVID-19.
Fungi:
Eukaryotic organisms, including yeasts, molds, and mushrooms.
Some fungi are beneficial (e.g., yeast used in bread and beer production), while others cause infections like athlete's foot.
Protozoa:
Single-celled eukaryotes, often found in water and soil.
Protozoa can be free-living or parasitic, causing diseases like malaria.
Algae:
Photosynthetic eukaryotes, which range from single-celled to multicellular organisms.
They are found in freshwater and marine environments and are essential for producing oxygen and forming the base of the aquatic food chain.
2. Structure of Microorganisms
Bacteria:
Bacteria have a simple structure with no true nucleus. Key parts include:
Cell Wall: Provides structure and shape.
Plasma Membrane: Regulates what enters and leaves the cell.
Cytoplasm: Jelly-like substance where cellular processes occur.
Ribosomes: Sites for protein synthesis.
DNA: Located in a nucleoid region, it controls the cell's functions.
Viruses:
Much simpler than cells, viruses consist of:
Capsid: Protein coat that encases the viral genetic material.
Nucleic Acid: DNA or RNA that carries the genetic information.
Envelope (optional): Some viruses have a lipid envelope that surrounds the capsid.
3. Growth and Reproduction of Microorganisms
Bacteria:
Reproduce by binary fission, where one cell divides into two identical daughter cells.
Growth can be rapid under optimal conditions, leading to exponential population increases.
Viruses:
Cannot reproduce independently. They need a host cell to replicate.
The viral life cycle includes attachment to the host cell, entry, replication of viral components, assembly of new viruses, and release from the host cell, often killing it.
Fungi:
Reproduce by forming spores, which can be sexual or asexual. Spores are resistant to harsh conditions and can germinate into new fungal organisms when favorable conditions return.
4. Importance of Microbiology
Human Health:
Microorganisms are essential in understanding human health and disease.
Pathogenic microorganisms cause diseases such as tuberculosis, influenza, and HIV.
Normal flora: The human body is home to beneficial microbes that aid in digestion, protect against pathogens, and produce vitamins.
Environmental Impact:
Microorganisms play a key role in nutrient cycling, decomposing organic matter, and cleaning up pollutants (bioremediation).
Photosynthetic microbes like algae are crucial in oxygen production and carbon fixation.
