Microorganisms : Friend and Foe — Question 10
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What are the major groups of microorganisms?
Microorganisms are classified into four major groups. These groups are:
- Bacteria — They are single celled. They do not have true nucleus or membrane bound cell organelles. They may be spherical, rod shaped or comma shaped.
- Fungi — They are multicellular.
- Protozoa — They are single celled.
- Algae — They may be single celled or multi cellular.
Chapter Overview: Microorganisms: Friend and Foe
Microorganisms are tiny living organisms visible only under a microscope. This chapter classifies them into five groups (bacteria, viruses, fungi, protozoa, algae) and explores their dual role as both beneficial (food production, medicine, agriculture) and harmful (causing diseases). Food preservation methods and the nitrogen cycle are key examination topics.
Board Exam Weightage: 5-7 marks | Difficulty: Moderate
Key Formulas & Concepts
| Concept | Details |
|---|---|
| Fermentation | Sugar converted to alcohol + CO2 by yeast (anaerobic process) |
| Pasteurisation | Heating milk to 70°C for 15-30 seconds, then rapid cooling |
| Nitrogen Fixation | N2 (atmospheric) converted to NH3/NO3- by Rhizobium or lightning |
| Antibiotics | Medicines that kill or stop growth of disease-causing bacteria; e.g., Penicillin from Penicillium |
Must-Know Concepts
- Viruses are not truly living; they reproduce only inside host cells
- Lactobacillus converts milk to curd by producing lactic acid
- Yeast is used in bread making (CO2 makes dough rise) and alcohol production
- Rhizobium in legume root nodules fixes atmospheric nitrogen
- Female Anopheles mosquito transmits malaria (Plasmodium)
- Antibiotics work ONLY against bacteria, NOT against viruses
Types of Microorganisms
| Type | Cell Structure | Unicellular/Multicellular | Examples |
|---|---|---|---|
| Bacteria | Prokaryotic | Unicellular | Lactobacillus, Rhizobium, Salmonella |
| Fungi | Eukaryotic | Both | Yeast, Penicillium, Mushroom |
| Protozoa | Eukaryotic | Unicellular | Amoeba, Plasmodium, Paramecium |
| Algae | Eukaryotic | Both | Chlamydomonas, Spirogyra |
| Virus | Non-cellular | Neither | Influenza virus, HIV, TMV |
Common Mistakes to Avoid
- Calling viruses living organisms (they are borderline)
- Thinking all bacteria are harmful (many are very useful)
- Confusing antibiotics (treat bacteria) with vaccines (prevent diseases)
- Believing antibiotics can cure viral infections
Scoring Tips
- Create a disease-pathogen-transmission table for quick reference
- Learn the nitrogen cycle as a flow diagram with all 5 steps
- Remember preservation methods using everyday kitchen examples
- Focus on NCERT exercise questions on food preservation
Frequently Asked Questions
Q: How many marks does this chapter carry in the exam?
A: Approximately 5-7 marks in the annual exam.
Q: What question types are commonly asked?
A: MCQs (1 mark), Very Short Answer (2 marks), Short Answer (3 marks), and Long Answer / Diagram (5 marks).
Q: Is this chapter important for competitive exams?
A: Yes, concepts from this chapter appear in NTSE, Olympiad, and other science competitions.