Biology — Microorganisms

Overview

Microorganisms form a foundational topic in upper-primary science, bridging basic biology with real-world applications in health, agriculture, and industry. For KAR TET Paper II, this topic tests your understanding of the diversity of microscopic life, their characteristics, and their roles—both beneficial and harmful—in daily life.

Questions typically focus on classification of microorganisms, distinguishing features of bacteria, viruses, fungi, and other groups, as well as their practical applications and diseases they cause. You must also understand the five-kingdom classification system proposed by Whittaker, which provides the conceptual framework for understanding where microorganisms fit in the living world.

Mastering this topic requires memorising key differences between groups, understanding life processes at the microscopic level, and connecting theoretical knowledge to observable phenomena like food spoilage, fermentation, and infectious diseases.

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Key Concepts

• **Microorganisms** are living organisms too small to be seen with the naked eye; they include bacteria, viruses, fungi, protozoa, and some algae.

• **Whittaker's Five-Kingdom Classification** divides all living organisms into Monera (bacteria), Protista (protozoa, some algae), Fungi, Plantae, and Animalia based on cell structure, mode of nutrition, and body organisation.

• **Bacteria** are unicellular prokaryotes (no true nucleus) with cell walls; they reproduce by binary fission and can be autotrophic or heterotrophic.

• **Viruses** are acellular—they lack cellular structure and are considered at the borderline of living and non-living; they reproduce only inside a host cell.

• **Fungi** are eukaryotic organisms with cell walls made of chitin; they are heterotrophic and obtain nutrition through saprophytic or parasitic means.

• **Protozoa** are unicellular eukaryotes, mostly found in aquatic environments, and include pathogens like Plasmodium (malaria) and Amoeba.

• **Useful microorganisms** help in food production (curd, bread, alcohol), medicine (antibiotics), agriculture (nitrogen fixation), and waste decomposition.

• **Harmful microorganisms** cause diseases in humans, animals, and plants; disease-causing microorganisms are called **pathogens**.

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Formulas / Key Facts

| Feature | Bacteria | Virus | Fungi | |---------|----------|-------|-------| | Cell type | Prokaryotic | Acellular | Eukaryotic | | Cell wall | Present (peptidoglycan) | Absent | Present (chitin) | | Reproduction | Binary fission | Inside host only | Spores, budding, fragmentation | | Nutrition | Autotrophic or heterotrophic | Parasitic only | Saprophytic or parasitic | | Example | Lactobacillus, Rhizobium | HIV, TMV, Bacteriophage | Yeast, Penicillium, Mushroom |