Microorganisms
Overview
Microorganisms are living things too small to be seen with the naked eye, requiring a microscope for observation. This topic forms a crucial part of the Life Sciences portion in Assam TET Paper II, connecting biology fundamentals with everyday applications like food preservation, disease prevention, and environmental cycles.
For the exam, you must understand the classification of microorganisms (bacteria, viruses, fungi, protozoa, algae), their structural features, modes of reproduction, and their dual role as both beneficial and harmful agents. Questions typically test factual recall about disease-causing organisms, useful applications in medicine and agriculture, and basic distinctions between different microbial groups.
Mastery of this topic also supports understanding of related areas like nutrition, respiration, and environmental pollution—making it a high-value section for integrated learning.
Key Concepts
- **Definition**: Microorganisms (microbes) are organisms invisible to the naked eye, including bacteria, viruses, fungi, protozoa, and some algae. They exist everywhere—soil, water, air, and inside living bodies.
- **Bacteria are prokaryotes**: They lack a true nucleus and membrane-bound organelles. Cell wall contains peptidoglycan. Shapes include cocci (spherical), bacilli (rod), spirilla (spiral), and vibrio (comma).
- **Viruses are non-cellular**: They consist only of genetic material (DNA or RNA) surrounded by a protein coat (capsid). They reproduce only inside living host cells, making them obligate parasites.
- **Fungi are eukaryotes**: They have a true nucleus, cell wall made of chitin, and obtain nutrition by decomposing organic matter (saprophytes) or living on hosts (parasites). Examples: yeast, mushroom, bread mould.
- **Protozoa are unicellular eukaryotes**: They move using cilia, flagella, or pseudopodia. Examples: Amoeba, Paramecium, Plasmodium (causes malaria).
- **Microorganisms can be beneficial or harmful**: Beneficial roles include fermentation, nitrogen fixation, decomposition, and antibiotic production. Harmful roles include causing diseases in plants, animals, and humans.
- **Antibiotics kill bacteria, not viruses**: This distinction is critical—viral diseases require vaccines or antiviral drugs, while bacterial infections respond to antibiotics like penicillin.
- **Pasteurisation and sterilisation**: Pasteurisation heats liquids to kill harmful microbes without destroying nutrients. Sterilisation completely eliminates all microbes.