Question

What are the major groups of microorganisms?
A. Bacteria, fungi
B. Protozoa, algae
C. Bacteria, fungi, protozoa, algae, and virus
D. Fungi, algae, and virus

Answer 1

Hint: Microorganisms are microscopic and can exist as unicellular (independent individual), multicellular, or in groups. They can be either eukaryotic or prokaryotic based on the group classification they belong to.

Complete answer:
Microorganisms are the microscopic organism that is widely spread in the ecosystem, dominating most of the conceivable environment. They are present even in the extreme climatic conditions of the ecosystem. They play a major role in the maintenance of the ecosystem. They can be both beneficial and harmful/hazardous. Based on morphology, cellular composition, reproduction, and means of locomotion they are of seven types: bacteria, fungi, algae, virus, archaea, protozoa, and multicellular animal parasites like helminths.

These can be divided into 5 major groups: bacteria, fungi, protozoa, algae, and virus.
- Bacteria are the prokaryotic (lack nucleus), a unicellular microscopic organism that undergoes reproduction by binary fission. They possess flagella for motility.
- Fungi: The group fungi include two members, yeast and molds. Yeasts are eukaryotic (with a true nucleus), unicellular fungi that reproduce asexually by budding, and molds are the eukaryotic, filamentous fungi that undergo asexual reproduction via spore formation.
- Viruses are the acellular infectious particles that can multiply only inside a living host. They consist of a nucleic acid core having either DNA or RNA as genetic material and this nucleic acid core is surrounded by a protein coat.
- Algae are also known as cyanobacteria or blue-green algae are the eukaryotic, unicellular, or multicellular, autotrophic microorganisms that undertake photosynthesis to produce their own food.
- Protozoa are the eukaryotic unicellular aerobic (requires oxygen to live) microorganisms. Protozoa cells have a nucleus, complex organelles, and cellulose in their cell wall.

Additional Information:
- Bacteria are the largest class of microorganisms that can be classified into different groups based on different characters like:
- Based on cell wall structure they can be differentiated into two major groups: gram-positive (cell wall having high peptidoglycans) and gram-negative (cell wall having loosely packed peptidoglycans) bacteria.
- Based on their response to oxygen they are classified as aerobic (requires oxygen for it to live), anaerobic (they live without oxygen) and facultative anaerobes (can live in both the conditions).
- Based on how they obtain their food or energy they are classified as heterotrophs (depend on others for food and energy), autotrophs (produce their own food using energy from light via photosynthesis), chemoautotrophs (produce their own food through a chemical reaction), and saprophytes (depend on dead and decayed organisms for their food and as an energy source)
- Archaea or Archaebacteria are considered under bacterial groups and differ from the true bacteria in lacking peptidoglycans in their cell wall, unlike true bacteria. Different sources of energy for archaea include hydrogen gas, sunlight, carbon dioxide, and sulphur. They take up sunlight through membrane pigment called bacteriorhodopsin, which reacts with sunlight to produce ATP as an energy molecule. Archaea can be classified into:
Methanogens: methane-producing organisms
Halophiles: microorganisms that can live in an extremely salty environment
Thermophiles: microbes that can live in extremely hot temperature
Psychrophiles: microbes that can live in extremely cold temperature
- Fungi are mostly multicellular except the yeast and they contain chitin in their cell wall. They form filamentous tubes called hyphae that help in the intake of nutrients from outside. Mycelium is the collection of hyphae. Based on the mode of nutrient intake they can be classified as:
Decomposers: obtain nutrients by absorbing organic materials from the environment
Parasites: depends on host organism (a harmful relationship with the host)
Symbionts: Symbiotic relationship with plants.
- Protozoa are grouped into autotrophs or heterotrophs based on the means of nutrients. They can also be classified based on the mode of locomotion into:
Flagellates: have a whip-like structure called flagella for locomotion and they are autotrophs.
Ciliates: tiny hair-like structure around their body called cilia help in locomotion
Pseudopods: forms false feet that are an extension of the body that is reverted back after the movement eg. Amoeboids
Non-motile sporozoans.
- Algae are the organisms that are believed to be the origins of green land plants. They produce oxygen and other carbohydrates that are used by other organisms.

Note: Multicellular animal parasites are the eukaryotic microbes like flatworms and roundworms also referred to as helminths. They have only a part of their life cycle as microscopic form, later they become large enough to see with naked eyes. Thus, they are discussed as a type of microbe but do not form the major group of microorganisms.