Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Micro-organisms in action
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Micro-organisms in action
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Subject: Biology
Class: Senior Secondary 1
Term: 3rd Term
Week: 2
Theme: The Organism And Its Environment
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Recognise the presence of microbes by the colonies the yform. Measure the rate of growth of microbes. List the beneficial effects of microbes from everyday'experiences. Recognise that some micro-or ganisms cause diseases. Recognise that somedisease causing mircoorganismsand air-borne, water-borne and are spread through our food.
This section provides the core content necessary for the teacher to deliver the lesson comprehensively. 2.
1. Defining Micro-organisms (Brief Recap) Micro-organisms, or microbes, are microscopic living organisms that are too small to be seen with the naked eye. They include bacteria, fungi (like yeasts and moulds), viruses, protozoa, and some algae. They are ubiquitous, found in soil, water, air, on surfaces, and within living organisms. 2.
2. Recognising the Presence of Microbes by Colony Formation Concept of Colonies: A colony is a visible mass of micro-organisms, typically bacteria or fungi, that grows from a single parent cell. When a single microbe lands on a suitable nutrient surface (like agar in a petri dish, or even a piece of bread), it multiplies rapidly through processes like binary fission (bacteria) or budding (yeast). With each division, the number of cells increases exponentially, eventually forming a macroscopic, discernible cluster – a colony.
Appearance of Colonies: Bacterial Colonies: Often appear as smooth, circular, irregular, or filamentous dots with distinct colours (white, cream, yellow, red, etc.) and textures (shiny, dull, mucoid, rough).
Examples: The spots of growth observed on stale food.
Fungal Colonies (Moulds): Typically appear fuzzy, cottony, powdery, or velvety, often displaying a variety of colours (green, black, blue, white, orange). They spread outwards as hyphae grow.
Examples: Mould on stale bread, fruits, or leather.
Yeast Colonies: Often look similar to bacterial colonies but can be slightly larger and creamier in texture.
Example: The foamy layer on fermenting burukutu or local palm wine.
Everyday Observations: Teachers can use examples like: Mould growing on bread, fruits (oranges, tomatoes) or leftover food. The foamy top on fermenting garri water or local brews like pito or burukutu. The 'scum' or greenish growth in stagnant water bodies (often algae or cyanobacteria, which are also microbes). The formation of a pellicle (a thin film) on the surface of local fermented products like ogi or fura de nono. 2.
3. Measuring the Rate of Growth of Microbes Microbial growth refers to an increase in the number of cells, not the size of individual cells. Measuring growth rate involves quantifying this increase over time.
Factors Affecting Growth Rate:
1. Temperature: Most microbes have an optimal temperature range. Too low, growth slows; too high, enzymes denature, and cells die. E.g., Refrigeration slows spoilage, boiling kills microbes.
2. Nutrients: Availability of food (carbon source, nitrogen, minerals) is crucial for energy and building blocks. 3. pH: Most microbes prefer a neutral pH (around 7). Extremes of acidity or alkalinity inhibit growth. E.g., Vinegar (acidic) is used as a preservative.
4. Oxygen: Some require oxygen (aerobes), some are poisoned by it (anaerobes), and some can grow with or without it (facultative anaerobes).
5. Moisture/Water Availability: Water is essential for metabolic activities. Dehydration inhibits growth. E.g., Drying food preserves it.
6. Presence of Inhibitors/Toxins: Antibiotics, disinfectants, or waste products can inhibit or kill microbes. Methods of Measurement (Conceptual for SS1): Direct Microscopic Count: Counting cells under a microscope using a counting chamber. (Limited for living/dead cells).
Standard Plate Count (Colony Counting): Diluting a sample and plating it on agar. After incubation, colonies are counted, and the original concentration is estimated (expressed as Colony Forming Units, CFU). This directly relates to objective
1. Turbidity Measurement: As microbes grow in a liquid medium, the medium becomes cloudy (turbid). A spectrophotometer can measure the amount of light scattered by the cells, correlating it to cell density. This is a rapid method.
Measuring Metabolic Activity: Quantifying the rate of consumption of nutrients or production of waste products (e.g., CO2).
Interpretation: A higher growth rate means microbes multiply faster, often leading to quicker spoilage or fermentation in controlled conditions. Understanding these rates is vital in food preservation and industrial microbiology. 2.
4. Beneficial Effects of Microbes from Everyday Experiences Microbes play indispensable roles in various aspects of life: Food Production and Fermentation: Yoghurt: Lactic acid bacteria (e.g., Lactobacillus, Streptococcus) ferment lactose in milk, producing lactic acid, which coagulates milk proteins, giving yoghurt its thick texture and tangy taste.
Bread: Yeast (Saccharomyces cerevisiae) ferments sugars in dough, products (e.g., CO2).
Interpretation: A higher growth rate means microbes multiply faster, often leading to quicker spoilage or fermentation in controlled conditions. Understanding these rates is vital in food preservation and industrial microbiology. 2.
4. Beneficial Effects of Microbes from Everyday Experiences Microbes play indispensable roles in various aspects of life: Food Production and Fermentation: Yoghurt: Lactic acid bacteria (e.g., Lactobacillus, Streptococcus) ferment lactose in milk, producing lactic acid, which coagulates milk proteins, giving yoghurt its thick texture and tangy taste.
Bread: Yeast (Saccharomyces cerevisiae) ferments sugars in dough, producing carbon dioxide gas (which makes bread rise) and alcohol (which evaporates during baking).
Garri Production: Micro-organisms (bacteria and fungi) ferment grated cassava, detoxifying it by breaking down cyanogenic glycosides and giving garri its characteristic sour taste and texture.
Ogi (Pap): Fermentation of maize, sorghum, or millet by lactic acid bacteria and yeasts.
Ogiri (Fermented Melon Seeds): Bacillus species ferment melon seeds, giving a strong flavouring agent.
Dawadawa (Fermented Locust Beans): Similar to ogiri, Bacillus species ferment locust beans, a crucial seasoning in West African cuisine.
Alcoholic Beverages: Yeast ferments sugars in grains (e.g., maize for burukutu, sorghum for pito) or fruits/palm sap for local wines, producing ethanol (alcohol).
Medicine and Health: Antibiotics: Many antibiotics (e.g., penicillin from the fungus Penicillium) are produced by micro-organisms to inhibit the growth of other microbes.
Vaccines: Some vaccines use weakened or killed micro-organisms or their components to stimulate immunity.
Probiotics: Beneficial bacteria (e.g., Lactobacillus in nunu or commercial yoghurt) that aid digestion and boost gut health.
Environmental Roles: Decomposition/Nutrient Cycling: Bacteria and fungi are primary decomposers, breaking down dead organic matter (plants, animals) into simpler substances, returning essential nutrients (nitrogen, carbon, phosphorus) to the soil. This is vital for soil fertility and waste management (composting).
Sewage Treatment: Microbes are used in wastewater treatment plants to break down organic pollutants.
Bioremediation: Using microbes to clean up pollutants in the environment (e.g., oil spills).
Industrial Applications: Enzyme Production: Microbes produce enzymes used in detergents, food processing, and textiles.
Biofuels: Microbes can produce ethanol and methane as alternative fuels. 2.
5. Micro-organisms Cause Diseases Pathogens: Micro-organisms that cause diseases are called pathogens. Types of Pathogenic Microbes and Diseases (Nigerian context): Bacteria: Typhoid fever (Salmonella typhi), Cholera (Vibrio cholerae), Tuberculosis (Mycobacterium tuberculosis), Tetanus (Clostridium tetani), Whooping cough (Bordetella pertussis), Bacterial Meningitis.
Viruses: Measles, Polio, HIV/AIDS, Lassa Fever, Hepatitis, Common Cold, Influenza, Ebola.
Fungi: Ringworm, Athlete's foot, Candidiasis (thrush).
Protozoa: Malaria (Plasmodium species - vector-borne, but the protozoan is the pathogen), Amoebiasis (Entamoeba histolytica), Giardiasis (Giardia lamblia).
Mechanism of Disease: Pathogens can cause disease by: Invading and multiplying in host tissues. Producing toxins (poisons) that damage host cells. Triggering an immune response that harms the host. 2.
6. Transmission Routes of Disease-Causing Micro-organisms Understanding how pathogens spread is critical for disease prevention.
Air-borne Diseases: Mechanism: Pathogens are released into the air in tiny droplets (aerosols) when an infected person coughs, sneezes, or talks. These droplets can then be inhaled by susceptible individuals.
Examples: Tuberculosis, Measles, Influenza (Flu), Common cold, Meningitis.
Prevention: Covering mouth/nose when coughing/sneezing, good ventilation, avoiding crowded places.
Water-borne Diseases: Mechanism: Pathogens contaminate water sources (wells, rivers, tap water) through faeces or urine of infected individuals. Ingestion of this contaminated water leads to infection.
Examples: Cholera, Typhoid fever, Amoebiasis, Giardiasis.
Prevention: Boiling water, using water filters, proper sewage disposal, protecting water sources from contamination, handwashing.
Food-borne Diseases (Food Poisoning): Mechanism: Pathogens (or their toxins) contaminate food through improper handling, inadequate cooking, cross-contamination, or use of contaminated water. Ingestion of contaminated food causes illness.
Examples: Food poisoning (caused by Salmonella, Staphylococcus aureus, E. coli), Typhoid fever (can also be food-borne).
Prevention: Washing hands before handling food, cooking food thoroughly, storing food at safe temperatures, avoiding cross-contamination (e.g., raw meat touching cooked food), washing fruits and vegetables. Other Transmission Routes (Brief Mention for completeness): Vector-borne: Transmitted by insects or animals (e.g., Malaria by mosquitoes, Lassa fever by rats). * Contact-borne: Pathogens (or their toxins) contaminate food through improper handling, inadequate cooking, cross-contamination, or use of contaminated water. Ingestion of contaminated food causes illness.
Examples: Food poisoning (caused by Salmonella, Staphylococcus aureus, E. coli), Typhoid fever (can also be food-borne).
Prevention: Washing hands before handling food, cooking food thoroughly, storing food at safe temperatures, avoiding cross-contamination (e.g., raw meat touching cooked food), washing fruits and vegetables. Other Transmission Routes (Brief Mention for completeness): Vector-borne: Transmitted by insects or animals (e.g., Malaria by mosquitoes, Lassa fever by rats). * Contact-borne: Direct contact with infected individuals or contaminated surfaces (e.g., skin infections, STIs). --- discuss practical prevention methods relevant to their local communities (e.g., boiling water, handwashing, covering food, proper waste disposal).
Student Activity: Students actively participate in the discussion, linking specific diseases to their transmission routes. They identify and discuss local prevention strategies. 3.
7. Conclusion and Wrap-up (5 minutes)
Teacher Activity: Summarise the key learning points: microbes are everywhere, they form colonies, their growth rate depends on conditions, they have beneficial uses (food, environment, medicine), but some cause diseases transmitted via air, water, and food. Reiterate the importance of hygiene.
Student Activity: Students ask clarifying questions and review their notes.
Resources: Samples: Mouldy bread, fermenting garri water, stagnant pond water.
Charts/posters: Diagrams of microbial colonies, lists of beneficial/harmful microbes, disease transmission routes. (Optional) Microscope and prepared slides (e.g., yeast, pond water). * Chalkboard/Whiteboard. ---
This topic has profound relevance to daily life in Nigeria, integrating into community, environment, and economy. Food Security and Local Economy (Food Processing and Preservation): Application: Understanding microbial action is fundamental to traditional Nigerian food processing. Fermentation by microbes is key to producing staple foods like garri (from cassava), ogi (from maize/millet), ogiri (from melon seeds), dawadawa (from locust beans), and local beverages like burukutu or palm wine. This knowledge helps improve processing techniques, ensures food safety, and contributes to the local economy by enhancing the shelf-life and value of agricultural products. Conversely, understanding spoilage by microbes guides preservation techniques like drying, salting, and refrigeration, reducing food waste and ensuring food availability.
Integration: Students can relate this to their family's food preparation methods, local markets selling fermented products, and community efforts to preserve harvests. Public Health and Sanitation (Disease Prevention): Application: A deep understanding of disease-causing micro-organisms and their transmission routes (air-borne, water-borne, food-borne) directly informs public health practices. For instance, knowing that cholera and typhoid are water-borne diseases caused by bacteria emphasizes the critical need for clean drinking water and proper sewage disposal, which are major challenges in many Nigerian communities. Knowledge about air-borne diseases like tuberculosis highlights the importance of good ventilation and covering coughs/sneezes. This empowers individuals to adopt preventive measures like handwashing, boiling water, and proper waste management, thereby reducing the incidence of infectious diseases.
Integration: This connects to community health campaigns, school hygiene programmes, and the need for improved sanitation infrastructure in Nigeria. Environmental Management (Waste Decomposition): Application: Micro-organisms are the primary decomposers in nature. They break down organic waste (dead plants, animal matter, household refuse) into simpler substances, recycling vital nutrients back into the soil. This process is crucial for maintaining soil fertility, which is essential for Nigeria's largely agrarian economy. In communities, understanding decomposition helps in effective waste management through composting, reducing landfill burden, and producing organic fertilizer for farms.
Integration: Students can observe compost heaps, discuss local waste disposal challenges, and consider how their communities manage organic waste. ---