Microorganisms

Organisms that can be seen only through an instrument called microscope. Hence, they are called microorganisms or microbes. Microbes can be seen and studied through microscope.

TYPES OF MICROORGANISMS

Bacteria (singular: bacterium): They are the most commonly found unicellular microorganisms. They can be rod-shaped (bacilli), spherical (cocci), comma-shaped (vibrio), and spiral (spirilla). They are found everywhere including the oceans and guts of animals. Ex. Lactobacillus, Yersinia Pestis, Vibrio Cholerae.
Algae (singular: alga): They are autotrophic microorganisms. Like plants, they have chlorophyll and cell walls in their cells. They can be either unicellular or multicellular. Algal cells found attached to each other are known as algal colonies. Their habitat include moist rocks, tree barks, soil and all kinds of water bodies. Ex. Nostoc and Volvox.
Fungi (singular: fungus): They lack chlorophyll and follow heterotrophic mode of nutrition. They can be unicellular or multicellular. Some multicellular fungi like mushrooms are visible to naked eye. They grow in dark, humid and moist places. Ex. Rhizopus, Agaricus, and Penicillium.
Protozoa (singular: protozoan): They are unicellular microbes showing animal-like characteristics such as movement and food-capture. Their habitats include freshwater or saltwater, soil and bodies of other organisms. Ex. Amoeba, Paramoecium, and Plasmodium (malarial parasite).
Viruses (singular: Virus): They can only be seen through an electron microscope because they are so small that they need to be magnified up to 200,000 times their original size to be observed. Ex. Bacteriophage, Adenovirus, and Influenza Virus.

It is difficult to classify them as living or non-living microorganisms. Viruses can only grow and multiply inside the cells of organisms (plants, animals, bacteria, etc.). Outside a host cell, they show no signs of life. This non-living state of a virus is called virion.

Bacteriophage: Viruses that infect bacteria

Some microorganisms