BIOLOGY CLASS NOTES: MICRO-ORGANISMS IN ACTION

SUBJECT: BIOLOGY CLASS: SENIOR SECONDARY SCHOOL 1 (S S 1) TOPIC: MICRO-ORGANISMS IN ACTION (FERMENTATION, DECAY, FOOD SPOILAGE, AND DISEASES) TERM: SECOND TERM

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INTRODUCTION

In our previous lessons, we identified the various types of micro-organisms, such as bacteria, viruses, fungi, protozoa, and certain algae. While many people associate micro-organisms (or microbes) only with "germs" and sickness, they are actually tireless biological "engineers" that work behind the scenes in our environment.

Micro-organisms are constantly "in action." They are metabolically active, meaning they take in nutrients, process them, and release waste products. These activities lead to major environmental and biological changes. This lesson explores the four major ways micro-organisms act: through Fermentation, Decay, Food Spoilage, and the causing of Diseases.

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COMPREHENSIVE CORE CONCEPTS

1. Fermentation: The Microscopic Bakery and Brewery

Fermentation is a metabolic process where micro-organisms, primarily yeast and certain bacteria, break down complex organic compounds (like sugars) into simpler substances (like alcohol or organic acids) in the absence of oxygen. This is a form of anaerobic respiration.

When yeast cells are added to a sugary dough or liquid, they "eat" the sugar. As they digest it, they produce Ethanol (alcohol) and Carbon dioxide ($CO_2$). In bread making, the $CO_2$ gas gets trapped in the dough, causing it to rise and become fluffy. In the production of palm wine or beer, the ethanol provides the alcoholic content.

Example in the Nigerian Context: In Nigeria, fermentation is essential for producing local staples. For instance, in the production of Garri, cassava mash is allowed to ferment for several days. During this time, micro-organisms break down the toxic cyanogenic glycosides in the cassava and produce the characteristic sour taste that Nigerians love. Similarly, Ogiri (melon seed) and Iru (locust beans) undergo fermentation to develop their unique flavors and aromas.

2. Decay (Decomposition): Nature’s Recycling Program

Decay is the process by which micro-organisms, known as saprophytes (mostly fungi and bacteria), break down the tissues of dead plants and animals. Without decay, the earth would be piled high with dead bodies, and the soil would run out of nutrients.

Saprophytes secrete powerful enzymes onto the dead organic matter. These enzymes break down complex proteins, carbohydrates, and fats into simple inorganic substances like nitrates, sulphates, and phosphates. These nutrients are then absorbed back into the soil, where they can be used again by living plants.

While decay can smell unpleasant due to the release of gases like hydrogen sulphide and ammonia, it is the most vital process for maintaining soil fertility and the balance of the ecosystem.

3. Food Spoilage: The Unwanted Guests

Food spoilage occurs when micro-organisms grow on our food, making it unattractive, foul-smelling, or dangerous to eat. This is essentially "decay" happening to the food we intend to eat.

Micro-organisms require moisture, the right temperature, and nutrients to grow. When we leave cooked rice on the counter overnight in a warm kitchen, bacteria like Staphylococcus or Bacillus multiply rapidly. They produce waste products that change the texture (making it slimy), the smell (making it sour or pungent), and the color of the food.

The Role of Enzymes: Some spoilage is caused by the micro-organisms' own enzymes which begin to digest the food. For example, mold growing on bread (Rhizopus) sends out "roots" called hyphae that release enzymes to liquefy the bread so the mold can absorb it.

4. Micro-organisms as Agents of Disease (Pathogens)

When a micro-organism enters the body of a host (like a human) and causes harm, it is called a Pathogen. These microbes interfere with the normal functioning of the body by destroying cells or producing toxins (poisons).

• Bacteria: Cause diseases like Typhoid fever (via Salmonella typhi) and Cholera (via Vibrio cholerae). They usually multiply rapidly and release toxins that cause inflammation and pain.
• Viruses: Cause diseases like Influenza, HIV/AIDS, and Ebola. They act like "hijackers," entering living cells and forcing them to produce more viruses.
• Protozoa: Cause Malaria (via Plasmodium) and Amoebic Dysentery.
• Fungi: Cause skin infections like Ringworm and Athlete’s foot.

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KEY POINTS (ELABORATED)

• Anaerobic Nature of Fermentation: Fermentation does not require oxygen. This allows microbes to thrive in sealed containers or deep within a mash of cassava.
• Saprophytic Nutrition: This is the specific mode of nutrition for decomposers. They perform "extracellular digestion"—digesting food outside their bodies before absorbing the liquid nutrients.
• The "Danger Zone" for Food: Micro-organisms that cause food spoilage thrive best between $20^\circ C$ and $45^\circ C$. This is why refrigeration ($4^\circ C$) is used to slow them down, and boiling is used to kill them.
• Pathogenicity: Not all microbes are bad. Only a small percentage are pathogenic. Most microbes are actually beneficial or neutral.
• Vectors: Many diseases caused by micro-organisms are carried by vectors. For example, the Anopheles mosquito is the vector that carries the malaria parasite from one person to another.

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MULTIPLE EXAMPLES

Table: Micro-organisms and their Specific Actions

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ENGAGING ACTIVITIES

Activity 1: The Balloon Fermentation Test

Objective: To observe micro-organisms (yeast) in action during fermentation. Instructions:

1. Mix one tablespoon of dry yeast and two tablespoons of sugar in a cup of warm water ($37^\circ C$).
2. Pour the mixture into a small plastic bottle.
3. Stretch a balloon over the mouth of the bottle.
4. Observe for 30 minutes. Observation: The balloon will begin to inflate. Discussion: Why did it inflate? The yeast is "eating" the sugar and breathing out $CO_2$ gas. This gas fills the balloon. This is exactly what happens inside bread dough!

Activity 2: The "Safe" Spoilage Observation

Objective: To identify signs of microbial action on food. Instructions:

1. Place a slice of moist bread in a transparent plastic bag and seal it.
2. Place another slice of very dry bread (toasted) in another bag and seal it.
3. Keep both in a dark cupboard for 5 days.
4. DO NOT OPEN THE BAGS once mold appears. Discussion: Notice which bread spoiled faster. (The moist one). Discuss how moisture is essential for microbial action.

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DETAILED SUMMARY

Micro-organisms are active living entities that significantly impact our lives through four main processes. Fermentation is a chemical breakdown of substances by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat; it is vital in the food industry for bread, yogurt, and local Nigerian foods like garri. Decay is the natural process of decomposition carried out by saprophytes, ensuring that nutrients are recycled back into the soil for plant growth.

Food Spoilage is an undesirable change in food's taste, smell, or appearance caused by microbial growth, which can be prevented by controlling temperature and moisture. Finally, micro-organisms act as Pathogens when they invade a host and cause Diseases. Understanding these roles allows us to harness the power of microbes for our benefit (industry and agriculture) while protecting ourselves from their harmful effects (food preservation and hygiene).