Question

What are microorganisms? Give examples.

Answer 1

Hint: Organisms which are so small that may or may not be visible with a naked eye are called microorganisms. They might be unicellular or multicellular and can even occur in a group of cells. Some of the microorganisms can be harmful to plant and animal life while others can be beneficial.

Complete Answer:
A microorganism is very tiny and is found almost everywhere on our planet. Microorganisms are also present inside human beings in millions. There can be 5 major classes of microorganisms, namely: Bacteria, Archaea, Algae, Fungi, and Protozoa.

1. Bacteria: Bacteria are single-celled prokaryotes. Bacteria were responsible for the origination of microbiology. They have 4 major shapes which are - Bacillus(rod like), Coccus(spherical), spirilla(spiral) and vibrio (curved).
- Bacteria have a cell wall which is made up of peptidoglycan and depending on the gram stain they take, they can be divided into gram positive and gram negative bacteria. The mode of reproduction in bacteria is Binary fission and mode of nutrition can be autotrophic or heterotrophic.
- They have a Flagella which helps them in propulsion and provides motility. Bacteria like Lactobacillus acidophilus act as a probiotic while bacteria like Vibrio cholerae causes water borne disease like Cholera.

2. Archaea: They are not true bacteria and thus lack peptidoglycan in their cell wall. Archaebacteria are adapted to love in extreme environments like hot springs, geothermal vents and polar ice caps. Archaea living in salt conditions are called Halophiles for example, Halobacterium salinarum and those living in hot temperatures are called Thermophiles, for example Thermus aquaticus.

3. Algae: Algae are eukaryotic organisms. They can be both unicellular or multicellular. A rigid cell wall is present and a green coloured pigment chlorophyll like that in plants are present in Algae. Algae produce their own food by the process of photosynthesis. They are found in moist and aquatic environments like soil, rocks and water bodies. Examples of Algae include Cyanobacteria or blue-green algae which can cause eutrophication in water bodies and Algae like Zooxanthellae live in a symbiotic association with corals.

4. Fungi: Fungi are eukaryotes which can be both unicellular and multicellular. They have a cell wall which is made up of a strong polysaccharide like chitin. They absorb nutrients from their environment by living either in a symbiotic association with a plant or by being in parasitic relationships with the host organisms. Fungi reproduce by sporulation. Example of a unicellular fungus is Yeast.

5. Protozoa: Protozoa are unicellular eukaryotes which perform aerobic respiration. They can have complex internal structures and show different types of motility. Protozoa like Amoeba use Pseudopodia or false feet for motility and for obtaining nutrition from the external environment. Other protozoa like Sporozoans are non motile and form spores which are dormant.

Note: Viruses are microorganisms which are considered to be on the borderline of living and nonliving organisms. They have their own genetic material but can only survive inside a living host. Recently discovered infectious agents called Prions refer to abnormally folded protein structures. They are very small but associated with many diseases.