Microorganisms: Friend and Foe
Class: VIII
Subject: Science
Chapter: 2
Learning Outcomes
What Students Will Achieve
Knowledge
- Classify microorganisms into four major groups
- Explain the role of microbes in food production
- Describe how vaccines provide immunity
- Understand the nitrogen cycle's importance
Understanding
- Analyze beneficial vs harmful microbial activities
- Explain fermentation and pasteurization processes
- Understand disease transmission mechanisms
- Recognize antibiotic resistance concerns
Skills
- Conduct yeast fermentation experiments
- Prepare microscope slides of pond water microbes
- Design public health posters about disease prevention
- Create models of nitrogen cycle
Types of Microbes
Major Groups of Microorganisms
Friend
Foe
Bacteria
Foe
Viruses
Friend
Foe
Fungi
Friend
Foe
Protozoa
| Type | Characteristics | Examples |
|---|---|---|
| Bacteria | Single-celled, prokaryotic, various shapes | Lactobacillus (curd), Rhizobium (N-fixation) |
| Fungi | Multicellular (except yeast), heterotrophic | Bread mold, Penicillium (antibiotics) |
| Protozoa | Single-celled, eukaryotic, motile | Amoeba, Plasmodium (malaria) |
| Viruses | Non-living outside host, DNA/RNA core | Influenza, HIV, COVID-19 virus |
Beneficial Microbes
Microorganisms as Friends
Food Production
- Curd: Lactobacillus bacteria
- Bread: Yeast fermentation
- Cheese: Bacterial cultures
- Alcohol: Yeast fermentation
Medicine Production
- Antibiotics: Penicillin from fungus
- Vaccines: Weakened microbes
- Insulin: Genetically modified bacteria
Environmental Uses
- Composting: Organic waste breakdown
- Nitrogen Fixation: Rhizobium in roots
- Bioremediation: Oil spill cleanup
Experiment: Yeast Fermentation
Objective: Observe CO₂ production during sugar fermentation
Materials: Yeast, sugar, warm water, balloon, test tube
Procedure:
- Mix yeast and sugar in warm water in test tube
- Cover mouth with balloon
- Observe balloon inflation over 30 minutes
- Test gas with lime water (turns milky = CO₂)
Harmful Microbes
Microorganisms as Foes
Disease-Causing Microorganisms
| Disease | Causative Agent | Transmission | Prevention |
|---|---|---|---|
| Cholera | Bacteria | Contaminated water | Vaccination, clean water |
| Malaria | Protozoa (Plasmodium) | Mosquito bite | Mosquito nets, repellents |
| COVID-19 | Virus (Coronavirus) | Airborne droplets | Masks, vaccination |
| Food Poisoning | Bacteria (Salmonella) | Spoiled food | Proper food storage |
Food Spoilage
Bread Mold
Fungal growth in moist conditions appears as fuzzy patches
Meat Decomposition
Bacterial action causes foul smell and texture changes
Case Study: Antibiotic Resistance
Objective: Understand dangers of antibiotic misuse
Scenario: Patient didn't complete antibiotic course
Task: Research and present how this leads to superbugs
Food Preservation
Methods to Prevent Food Spoilage
Heat/Cold Treatment
- Pasteurization: Milk heated to 70°C
- Refrigeration: Slows microbial growth
- Canning: Heat sterilization
Chemical Methods
- Salting: Fish, pickles
- Sugaring: Jams, jellies
- Vinegar: Pickling vegetables
Storage Methods
- Vacuum Packing: Removes oxygen
- Airtight Containers: Prevents contamination
- Drying: Removes moisture
Project: Compare Preservation Methods
Objective: Test which method best preserves bread
Groups: Refrigeration, airtight container, room temperature
Duration: 1-week observation with daily records
Nitrogen Cycle
Role of Microbes in Nitrogen Cycle
Nitrogen Cycle Processes
| Process | Microbial Role | Importance |
|---|---|---|
| Nitrogen Fixation | Rhizobium in root nodules | Converts atmospheric N₂ to usable forms |
| Nitrification | Soil bacteria (Nitrosomonas) | Converts ammonia to nitrates |
| Denitrification | Pseudomonas bacteria | Returns nitrogen to atmosphere |
Model Making: Nitrogen Cycle
Objective: Create 3D model showing microbial roles
Materials: Clay, paper, colors, labels
Evaluation: Accuracy, creativity, presentation
Assessment
Evaluation Strategies
Formative Assessments
- Microscope drawing of pond microbes
- Quiz on disease transmission
- Lab report on fermentation
- Poster on beneficial microbes
Summative Assessments
- Unit test (MCQ + short answer)
- Model presentation of nitrogen cycle
- Research paper on antibiotic resistance
- Practical exam on food preservation
Sample Questions
Higher Order Thinking Questions
- Why are viruses considered borderline between living and non-living?
- Compare the roles of yeast in bread-making and alcohol production
- How would the nitrogen cycle be affected if all microbes disappeared?
- Design an experiment to test the effectiveness of different food preservatives
