02. Class 8 Science Chapter 2 Microorganisms – Friend and Foe Notes for CBSE
Welcome to Class 8 Science Chapter 2 Microorganisms – Friend and Foe Notes for CBSE
Chapter 2: Microorganisms: Friend and Foe
2.1 Microorganisms
Introduction
- Microorganisms, or microbes, are tiny living organisms, invisible to the naked eye.
- To observe them, microscopes are required due to their minuscule size.
Classification of Microorganisms
Microorganisms can be categorized into four main groups:
- Bacteria: Abundant single-celled organisms with various shapes and sizes.
- Fungi: Includes molds and yeasts, responsible for processes like bread rising and organic matter decomposition.
- Protozoa: Single-celled, mobile creatures often found in water, vital in aquatic ecosystems.
- Some Algae: Diverse in size and shape, playing essential roles in aquatic food chains.
Unique Characteristics
- A unique group among microorganisms is viruses, which cannot reproduce independently and rely on host organisms.
- Microorganisms are diverse and impact our lives by causing various diseases like the common cold, polio, and chickenpox.
- Protozoa can cause diseases such as dysentery and malaria, while bacteria lead to conditions like typhoid and tuberculosis.
2.2 Where do Microorganisms Live?
Diverse Habitats
- Microorganisms adapt to various environments, from polar regions to hot springs, deserts, and wetlands.
- They can thrive inside the bodies of animals, including humans.
Microorganisms as Parasites
- Some microorganisms are parasites, living on other organisms and causing diseases.
- Others lead independent lives, not relying on other organisms.
2.3 Microorganisms and Us
Beneficial Uses
- Microorganisms have numerous beneficial uses:
- They enable the production of alcohol through yeast fermentation, used in beverages like wine and beer.
- Microorganisms assist in food preparation, including curd, bread, and cakes.
- They are vital in fermenting food products like cheese, yogurt, and sauerkraut.
- Microorganisms contribute to environmental cleanup by breaking down organic waste.
- They are crucial in pharmaceuticals, aiding in the production of medicines and antibiotics like penicillin.
2.4 Harmful Microorganisms
Threats from Microorganisms
- Microorganisms pose threats by causing diseases and spoiling food.
- Some microorganisms, known as pathogens, are responsible for diseases affecting humans, plants, and animals.
- Diseases can spread through air, water, food, and physical contact.
- Examples of communicable diseases include cholera, the common cold, chickenpox, and tuberculosis.
Disease Transmission
- Insects and animals can serve as carriers, aiding in the transmission of disease-causing microorganisms.
- Microorganisms can spoil food, making it unsafe to eat.
2.5 Food Preservation
Methods of Food Preservation
- To prevent microbial spoilage, various food preservation methods are used:
- Chemical Preservation: Substances like salt, sugar, and edible oils inhibit microorganism growth.
- Salt Preservation: Used for preserving meat and fish by drawing out moisture.
- Sugar Preservation: Used for products like jams and jellies by creating an unfavorable environment for microorganisms.
- Use of oil and vinegar in preserving pickles.
- Heat treatments, like pasteurization, kill many microorganisms in food.
- Proper storage and packaging are crucial to prevent contamination and spoilage.
2.6 Nitrogen Fixation
The Process of Nitrogen Fixation
- Nitrogen fixation converts atmospheric nitrogen into a form plants can use.
- Certain soil bacteria and blue-green algae perform nitrogen fixation.
- Fixed nitrogen becomes accessible to plants through their root systems.
Recycling Nitrogen
- When plants and animals die, other microorganisms break down their nitrogen-containing waste and return it to the soil.
- Some bacteria convert nitrogen compounds into nitrogen gas, which is released back into the atmosphere.
2.7 Nitrogen Cycle
The Nitrogen Cycle
- The nitrogen cycle describes how nitrogen is continually recycled.
- The atmosphere is primarily composed of nitrogen gas (about 78%).
- Nitrogen fixation converts atmospheric nitrogen into compounds for plants.
- Plants and animals consume these compounds, and when they die, nitrogen returns to the environment.
- Some nitrogen is released back into the atmosphere.
Keywords and Definitions
Important Keywords for Class 8 Science Chapter 2 Microorganisms – Friend and Foe Notes for CBSE
- Microorganisms: Also known as microbes, these are tiny living organisms, often invisible to the naked eye, which include bacteria, fungi, protozoa, and some algae.
- Bacteria: Microscopic single-celled organisms with various shapes and sizes, found in a wide range of environments.
- Fungi: A group of microorganisms including molds and yeasts, with key roles in processes like bread rising and organic matter decomposition.
- Protozoa: Single-celled, mobile creatures, commonly found in water, and vital in aquatic ecosystems.
- Algae: Diverse microorganisms, often found in aquatic environments, and serving essential roles in aquatic food chains.
- Viruses: Unique microorganisms that cannot reproduce independently and rely on host organisms for their replication.
- Common Cold: A viral infection that affects the upper respiratory tract, causing symptoms like a runny nose and cough.
- Polio: A highly contagious viral infection that can lead to paralysis, especially in children.
- Chickenpox: A contagious viral disease characterized by itchy rashes and flu-like symptoms.
- Dysentery: An infection caused by protozoa, leading to severe diarrhea with blood and mucus.
- Malaria: A tropical disease caused by protozoa and transmitted through mosquito bites, resulting in fever and often severe illness.
- Typhoid: A bacterial disease that can lead to high fever, weakness, and abdominal pain.
- Tuberculosis (TB): A bacterial infection that primarily affects the lungs and can be transmitted through the air.
Questions and Answers
Important Questions for Class 8 Science Chapter 2 Microorganisms – Friend and Foe Notes for CBSE.
FAQs
Q1: What are microorganisms, and where can they be found?
A1: Microorganisms, often called microbes, are tiny living organisms such as bacteria, fungi, protozoa, and some algae. They can be found in various environments, including soil, water, and even the human body.
Q2: How do microorganisms impact food preservation?
A2: Microorganisms can either spoil or preserve food. For instance, certain bacteria are used in making yogurt and cheese, preserving these dairy products.
Q3: What is pasteurization, and how does it help in food safety?
A3: Pasteurization is a heat treatment process that kills harmful microorganisms in food and beverages. It ensures food safety by reducing the risk of microbial contamination.
Q4: What role do microorganisms play in nitrogen fixation?
A4: Microorganisms, like Rhizobium bacteria, can fix atmospheric nitrogen in the soil, making it accessible to plants and enhancing soil fertility.
Q5: Can microorganisms be harmful to humans?
A5: Yes, some microorganisms, like pathogenic bacteria and viruses, can cause diseases in humans.
Q6: How do antibiotics work, and when should they be used?
A6: Antibiotics are drugs that kill or inhibit the growth of disease-causing microorganisms. They should be used under a doctor’s guidance and only when necessary.
Q7: What is fermentation, and how is it used in food production?
A7: Fermentation is a metabolic process carried out by microorganisms like yeast to convert sugars into alcohol or acids. It is used in making bread, beer, and yogurt.
Q8: What are some common diseases caused by microorganisms?
A8: Common diseases caused by microorganisms include tuberculosis, cholera, malaria, and the common cold.
Q9: How do microorganisms contribute to the environment’s health?
A9: Microorganisms help break down organic matter, clean up pollutants, and enhance soil fertility, thereby contributing to environmental balance.
Q10: Can microorganisms survive in extreme conditions?
A10: Yes, microorganisms are incredibly hardy and can thrive in extreme environments such as hot springs, cold waters, and even in outer space.
MCQs
Q1: What are microorganisms primarily composed of?
- a) Water
- b) Carbon
- c) Cells
- d) Light
Answer: c) Cells
Q2: Which of the following is a common use of yeast?
- a) Cleaning
- b) Baking
- c) Medicine
- d) Construction
Answer: b) Baking
Q3: What is the primary role of antibiotics?
- a) Promote growth
- b) Prevent fermentation
- c) Kill or inhibit microorganisms
- d) Enhance soil fertility
Answer: c) Kill or inhibit microorganisms
Q4: Which microorganism causes diseases like polio and chickenpox?
- a) Bacteria
- b) Protozoa
- c) Viruses
- d) Fungi
Answer: c) Viruses
Q5: What does pasteurization do to food and beverages?
- a) Increases acidity
- b) Reduces microbial contamination
- c) Enhances flavor
- d) Reduces nutritional value
Answer: b) Reduces microbial contamination
Q6: In the nitrogen cycle, which microorganisms convert nitrogen gas into usable compounds?
- a) Fungi
- b) Protozoa
- c) Bacteria
- d) Viruses
Answer: c) Bacteria
Q7: What is the primary method of preserving food using oil and vinegar?
- a) Salting
- b) Fermentation
- c) Canning
- d) Pickling
Answer: d) Pickling
Q8: What is the most common method of preserving fruits like jams and jellies?
- a) Salting
- b) Canning
- c) Sugaring
- d) Pickling
Answer: c) Sugaring
Q9: Which of the following is not a common disease caused by microorganisms?
- a) Tuberculosis
- b) Typhoid
- c) Diabetes
- d) Malaria
Answer: c) Diabetes
Q10: What is the primary role of Rhizobium bacteria in the nitrogen cycle?
- a) Converting nitrogen gas into compounds
- b) Fixing atmospheric carbon
- c) Enhancing soil acidity
- d) Promoting algae growth
Answer: a) Converting nitrogen gas into compounds
This was the end of Class 8 Science Chapter 2 Microorganisms – Friend and Foe Notes for CBSE.
For more information, refer to NCERT SOLUTIONS, NCERT NOTES, and NCERT BOOKS .
