Microorganisms Friends And Foe – Complete Guide For Class 8 Science Chapter 2

Welcome to iPrep, your Learning Super App. Our learning resources for the chapter, Microorganisms: Friend and Foe in Science Class 8th Chapter 2 are designed to ensure that you grasp this concept with clarity and perfection. Whether you’re studying for an upcoming exam or strengthening your concepts, our engaging animated videos, practice questions and notes offer you the best of integrated learning with interesting explanations and examples.

The concept of Microorganisms in Class 8 Science introduces students to a comprehensive understanding of microorganisms as an integral part of the natural world, playing pivotal roles in various ecosystems and human industries. This topic explores the dual nature of microorganisms—how they can be both beneficial allies and harmful adversaries. Let us Understand their diversity, functions, and impacts is crucial for harnessing their benefits while minimizing their risks.

Microorganisms: Friend and Foe – 

Microorganisms are tiny living organisms that are invisible to the naked eye, yet they play a significant role in our lives and the environment. They can be both beneficial and harmful, making it essential to understand their classification and functions.

Classification of Microorganisms

Understanding the classification of microorganisms helps us appreciate their dual roles as friends and foes. 

Bacteria

• Description: Bacteria are unicellular microorganisms with various shapes, such as rods, spheres, and spirals.
• Examples:
  • Lactobacillus (rod-shaped) helps in the formation of curd.
  • Streptococcus (spherical-shaped) can cause infections like strep throat.
  • Vibrio (spiral-shaped) is known for causing diseases like cholera.

Fungi

• Description: Fungi are mostly multicellular microorganisms that decompose organic matter.
• Examples:
  • Aspergillus and Penicillium are used in the production of antibiotics like penicillin.
  • Molds that spoil bread and other foods are also fungi.

Protozoa

• Description: Protozoa are unicellular microorganisms, often found in water, that can reproduce both sexually and asexually.
• Examples:
  • Amoeba and Paramecium are commonly studied protozoa.
  • Protozoa like Plasmodium cause malaria.

Algae

• Description: Algae are typically autotrophic microorganisms that can be unicellular or multicellular.
• Examples:
  • Chlamydomonas (unicellular) and Spirogyra (multicellular) are examples of algae found in aquatic environments.

Viruses

• Description: Viruses are non-cellular entities that require a host to reproduce.
• Examples:
  • They cause diseases like the common cold and influenza.

Observing Microorganisms Yourself

To observe microorganisms:

1. Take a beaker and add some moist soil from a field.
2. Add water to the beaker.
3. Observe a drop of water from the beaker under a microscope.

Alternatively:

1. Take a few drops of water from a pond.
2. Spread these drops on a glass slide and observe them through a microscope.

Where Do Microorganisms Live?

Microorganisms can survive in all types of climates, from hot springs to icy environments. They are also found inside the bodies of animals, including humans.

• Hot Springs: Home to thermophilic bacteria.
• Cold Environments: Inhabitants include Pseudomonas syringae.

Experiment: Growing Microorganisms

1. Take some agar gel and boil it in water.
2. Dissolve some sugar and transfer the solution to a petri dish.
3. Keep the dish open for a few hours.
4. Store it in a dark and warm place for a few days.
5. Observe the petri dish for spots on the culture medium. Take a small part of the colony and observe it under a microscope.

Microorganisms and Us

Microorganisms play a vital role in our lives. Some are beneficial, while others are harmful and can cause diseases.

Friendly Microorganisms

Microorganisms are used for various purposes such as:

• Curd: Lactobacillus bacteria are used to ferment milk into curd.
• Bread: Yeast is used in the production of bread, causing the dough to rise.
• Medicines: Microorganisms are used to produce antibiotics, which kill or stop the growth of disease-causing microorganisms.

Do You Know Who This Is?

Louis Pasteur was a French biologist known for his discoveries in the principles of vaccination, microbial fermentation, and pasteurization. His discoveries have been crucial in harnessing the beneficial aspects of microorganisms while protecting us from their harmful effects.

Experiment: Fermentation

Fermentation involves the use of microorganisms, particularly yeast, to convert sugars into alcohol and carbon dioxide. Steps to carry out Fermentation involves-

1. Take a beaker and fill it half with water.
2. Dissolve 2-3 teaspoons of sugar in it and add half a spoon of yeast powder to the sugar solution.
3. Keep it covered in a warm place for 4-5 hours.

Result: The smell of alcohol indicates that sugar has been converted into alcohol by yeast. This process is known as fermentation.

Vaccination

Vaccination involves introducing weakened or inactive microorganisms into the body to stimulate the immune system and build immunity against diseases. The body fights and kills them by producing suitable antibodies, which remain in the body to protect against future infections.

Do You Know Who This Is?

Edward Jenner developed the first vaccine against smallpox in 1796 by using microorganisms from cowpox lesions, demonstrating that exposure to certain microorganisms could provide immunity against related diseases.

Soil Fertility

Some microorganisms like bacteria and blue-green algae can fix nitrogen from the atmosphere, enriching the soil with nitrogen and increasing its fertility.

Cleaning the Environment

Microorganisms play a crucial role in cleaning the environment by decomposing waste matter and converting it into manure. In fields, microorganisms decompose dead plants and animals, converting them into simple substances used by other plants and animals.

Food Preservation

Microorganisms can spoil food, causing it to emit a bad smell, taste, and change color. Spoiled food is injurious to health and can cause food poisoning. Food preservation is necessary to prevent microbial attacks.

Methods of Food Preservation

Methods of food preservation inhibit or eliminate harmful microorganisms to extend food’s shelf life and ensure safety.

• Chemical Methods: Salts and edible oils are common preservatives used to inhibit microbial growth.
• Common Salt: Used to preserve meat, fish, amla, raw mangoes, etc.
• Sugar: Reduces moisture content, inhibiting bacterial growth.
• Oil and Vinegar: Prevent spoilage of pickles by creating an inhospitable environment for bacteria.
• Heat & Cold Treatments: Boiling kills many microorganisms, while low temperatures inhibit microbial growth.
• Pasteurization: Involves heating milk to about 70°C for 15 to 30 seconds and then chilling it to kill harmful microbes.

Harmful Microorganisms

Microorganisms can be harmful, causing diseases in humans, plants, and animals. Disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing, and leather.

Disease-Causing Microorganisms

Disease-causing microorganisms, such as bacteria, viruses, and protozoa, can lead to various illnesses in humans by entering the body through the air, water, food, or direct contact. 

In Humans

Pathogens can enter the human body through:

• The air we breathe
• The water we drink
• The food we eat
• Direct contact with an infected person

Communicable Diseases: Diseases caused by microorganisms and transmitted from an infected person or animal to another healthy person or animal. Examples include cholera, common cold, chickenpox, and tuberculosis.

Carriers: Microbial diseases can be transferred through insects and animals acting as carriers. For example, the female Anopheles mosquito carries the parasite of malaria, while the female Aedes mosquito carries the dengue virus.

Human Diseases

Different diseases are caused by specific microorganisms, each with its own unique mode of transmission.

• Tuberculosis: Caused by bacteria; transmission through air.
• Chickenpox and Polio: Caused by viruses; transmission through air.
• Cholera and Typhoid: Caused by bacteria; transmission through water.
• Malaria: Caused by protozoa; transmission through mosquitoes.

Preventive Measures: To treat diseases caused by microorganisms, the following cures are available:

• Vaccination
• Maintaining personal hygiene and good sanitary habits
• Consuming properly cooked food and boiled drinking water
• Using mosquito nets and repellents
• Spraying insecticides and controlling mosquito breeding

Food Poisoning

Microorganisms in food can sometimes produce toxic substances, making the food toxic and causing food poisoning. Preserving food is crucial to prevent spoilage.

In Animals

Microorganisms also cause diseases in animals. For example, anthrax is a dangerous disease in humans and cattle caused by the bacterium Bacillus anthracis. Foot and mouth disease in cattle is caused by a virus.

Do You Know Who This Is?

Robert Koch was a German physician who identified the specific microorganisms responsible for tuberculosis, cholera, and anthrax.

In Plants

Microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, and orange. These diseases reduce crop yield and can be controlled by using chemicals that kill the microbes.

Plant Diseases

• Citrus Canker: Caused by bacteria; transmission through air.
• Yellow Vein Mosaic of Bhindi (Okra): Caused by a virus; transmission through insects.
• Rust of Wheat: Caused by fungi; transmission through air and seeds.

The Nitrogen Cycle 

Nitrogen constitutes 78% of our atmosphere and is essential for all living organisms as part of proteins, chlorophyll, nucleic acids, and vitamins. Since plants and animals cannot directly utilize atmospheric nitrogen, microorganisms play a crucial role in the nitrogen cycle by converting it into forms that are accessible to them. When plants and animals die, bacteria and fungi in the soil convert nitrogenous wastes into nitrogen compounds that plants can use. Certain bacteria convert some of these compounds back into nitrogen gas, maintaining the atmospheric nitrogen balance.

Nitrogen Fixation 

Nitrogen fixation converts atmospheric nitrogen into nitrogen compounds that plants can use. Microorganisms, such as the bacterium Rhizobium is involved in nitrogen fixation in leguminous plants, such as beans and peas, through a symbiotic relationship.

This comprehensive guide offers an in-depth exploration of the essence of Microorganisms: Friend and Foe, highlighting their beneficial and harmful effects. Microorganisms are an integral part of our ecosystem, playing diverse roles from supporting human health and agriculture to being involved in the nitrogen cycle. Understanding their functions can help us utilize their benefits while mitigating their harmful effects.