Microorganisms

Microorganisms

Overview

Microorganisms (or microbes) are living things too small to be seen with the naked eye. They include bacteria, viruses, fungi, protozoa, and algae. This topic forms a core part of the Science section in UPTET Paper II and connects biology with everyday life, health, agriculture, and the environment.

For UPTET, you must know the classification of microorganisms, their basic structure, and most importantly, their useful and harmful roles. Questions often test whether you can distinguish between types of microbes, recall examples of diseases caused by each, and identify beneficial applications like fermentation, nitrogen fixation, and antibiotic production. A clear understanding of this topic also supports pedagogy questions on how to teach life sciences through real-world examples.

Master the characteristics that separate bacteria from viruses from fungi, memorise key disease-microbe pairs, and understand the economic importance of microbes in food, medicine, and agriculture.

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Key Concepts

• Microorganisms are classified into five major groups: bacteria, viruses, fungi, protozoa, and algae. Of these, viruses are unique because they show living characteristics only inside a host cell.
• Bacteria are single-celled prokaryotes (no true nucleus). They can be spherical (cocci), rod-shaped (bacilli), or spiral (spirilla). Some are autotrophic; most are heterotrophic.
• Viruses are non-cellular and acellular—they consist of genetic material (DNA or RNA) surrounded by a protein coat. They reproduce only inside living cells and are hence called obligate parasites.
• Fungi may be unicellular (yeast) or multicellular (mushrooms, moulds). They are eukaryotic, lack chlorophyll, and obtain food by absorbing nutrients from dead or living organic matter (saprophytes or parasites).
• Protozoa are unicellular eukaryotes found in water and soil. Examples: Amoeba, Paramecium, Plasmodium (causes malaria).
• Algae are simple, chlorophyll-containing organisms—mostly aquatic. They perform photosynthesis and are primary producers in aquatic ecosystems.
• Microorganisms can be useful or harmful. Useful roles include fermentation, decomposition, nitrogen fixation, antibiotic production, and vaccine preparation. Harmful roles include causing diseases in humans, animals, and plants, as well as food spoilage.
• Antibiotics are medicines derived from microorganisms (mainly fungi and bacteria) that kill or inhibit other microorganisms. Example: Penicillin from the fungus Penicillium.

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Formulas / Key Facts

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Worked Examples

Example 1: Identifying the microorganism type

Question: Which type of microorganism causes the common cold?

Solution:

1. The common cold is caused by viruses (mainly rhinoviruses).
2. Viruses are non-cellular, need a living host to multiply.
3. Therefore, answer: Virus.

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Example 2: Useful role of microorganisms

Question: How is curd formed from milk? Name the microorganism involved.

Solution:

1. Milk contains lactose (milk sugar).
2. When a small amount of curd (containing Lactobacillus bacteria) is added to warm milk, Lactobacillus multiplies.
3. Lactobacillus converts lactose into lactic acid.
4. Lactic acid causes the milk protein (casein) to coagulate, turning milk into curd.
5. Microorganism: Lactobacillus (a bacterium).

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Example 3: Disease-pathogen matching

Question: Match the disease with its causative microorganism:

Solution:

• Malaria → (d) Protozoan (Plasmodium, spread by Anopheles mosquito)
• Typhoid → (b) Bacterium (Salmonella typhi, spreads through contaminated water/food)
• Ringworm → (c) Fungus (affects skin; not caused by a worm despite the name)
• Dengue → (a) Virus (spread by Aedes mosquito)

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Common Mistakes

1. Thinking viruses are living organisms in all conditions. Viruses show living properties (reproduction) only inside a host cell. Outside, they behave like non-living particles. Correct view: Viruses are at the borderline of living and non-living.
2. Confusing bacteria and viruses in disease questions. Students often mix them up. Remember: common cold, influenza, dengue, polio = viral; TB, cholera, typhoid = bacterial. Create a mental list grouped by pathogen type.
3. Assuming all microorganisms are harmful. Many questions test useful microbes. Yeast (bread, alcohol), Lactobacillus (curd), Rhizobium (nitrogen fixation), Penicillium (antibiotic) are beneficial.
4. Calling ringworm a worm-caused disease. Despite the name, ringworm is a fungal infection of the skin. The circular rash resembles a worm shape, hence the misleading name.
5. Forgetting that antibiotics do not work on viruses. Antibiotics kill bacteria, not viruses. Viral infections (like cold, flu) cannot be cured by antibiotics—only supportive treatment or antiviral drugs help.

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Quick Reference

• Bacteria: Prokaryotic, single-celled; shapes—cocci, bacilli, spirilla; examples—Lactobacillus, Rhizobium, Salmonella.
• Viruses: Non-cellular, need host to reproduce; examples—rhinovirus, HIV, dengue virus.
• Fungi: Eukaryotic, no chlorophyll, saprophytic or parasitic; examples—yeast, Penicillium, mushroom.
• Useful microbes: Fermentation (yeast), curd (Lactobacillus), nitrogen fixation (Rhizobium), antibiotics (Penicillium).
• Harmful microbes: Cause diseases—TB (bacteria), malaria (protozoa), ringworm (fungus), dengue (virus).
• Preservation methods: Pasteurisation, refrigeration, salting, adding sugar/oil, drying—all reduce microbial growth.