Microorganisms Friends And Foe Class 8 Science Chapter 2 Notes

Microorganisms Friends And Foe Class 8 Science Chapter 2 Notes area available here. These notes have been prepared by the subject experts of our website CBSE Wale.

Microorganisms Friends And Foe Class 8 Science Chapter 2 Notes

Introduction

• Microorganisms or microbes are living organisms that are often too small to be seen without magnification.
• Examples include bacteria, fungi, protozoa, and viruses.
• Microorganisms play various roles in ecosystems, including decomposition and nutrient cycling.
• Observation of spoiled moist bread during the rainy season reveals greyish white patches on its surface.
• Examination under a magnifying glass shows tiny, black rounded structures within these patches.
• These structures are likely to be fungal spores, which contribute to the bread’s spoilage and are responsible for the observed changes.

Microorganisms

• Water and soil harbor numerous tiny organisms, including microorganisms or microbes.
• Not all of these organisms fall strictly into the category of microbes.
• Microbes are extremely small and cannot be seen with the naked eye.
• Some, like the fungus growing on bread, can be observed with a magnifying glass.
• Others are only visible with the aid of a microscope.
• Microorganisms are termed as such because of their minute size, requiring magnification for observation.
• Microorganisms are classified into four major groups: Bacteria, Fungi, Protozoa and Some algae.
• Viruses are distinct from other microorganisms and reproduce only inside host cells.
• They can infect various types of organisms including bacteria, plants, and animals.
• Common illnesses such as cold, influenza (flu), and coughs are caused by viruses.
• Serious diseases like polio and chickenpox are also caused by viruses.
• Dysentery and malaria are caused by protozoa (protozoans).
• Typhoid and tuberculosis (TB) are bacterial diseases.

Where do Microorganisms Live?

• Microorganisms include single-celled organisms like bacteria, some algae, and protozoa, as well as multicellular organisms like certain algae and fungi.
• They inhabit diverse environments, from icy climates to hot springs, and from deserts to marshlands.
• Microorganisms can reside inside the bodies of animals, including humans.
• Some microorganisms are parasitic and grow on other organisms, while others live independently.

Microorganisms and Us

• Microorganisms have significant impacts on our lives.
• Some microorganisms are beneficial and serve various purposes.
• Others can be harmful and are responsible for causing diseases.

Friendly Microorganisms

• Microorganisms are utilized for diverse purposes.
• They are employed in food production processes such as curd, bread, and cake preparation.
• Microorganisms have long been used in alcohol production.
• They play a role in environmental cleanup by breaking down organic waste into harmless substances.
• Bacteria are also involved in medicine production.
• In agriculture, microorganisms are utilized to enhance soil fertility by nitrogen fixation.

Making of Curd and Bread

• Curd contains various microorganisms, with the bacterium Lactobacillus being crucial for curd formation.
• Lactobacillus multiplies in milk and transforms it into curd through fermentation.
• Bacteria play roles in producing cheese, pickles, and other food items.
• Curd is an essential ingredient in dishes like rava (sooji) idlis and bhaturas.
• Bacteria and yeast aid in the fermentation process for rice idlis and dosa batter.
• Yeast reproduces quickly and generates carbon dioxide during respiration.
• The gas bubbles produced by yeast fill the dough, increasing its volume.
• This process forms the foundation for yeast’s use in the baking industry for breads, pastries, and cakes.

Commercial Use of Microorganisms

• Microorganisms are utilized in large-scale production processes for alcohol, wine, and acetic acid (vinegar).
• Yeast is specifically employed for commercial production of alcohol and wine.
• Yeast is cultivated using natural sugars found in grains such as barley, wheat, rice, and crushed fruit juices.
• The aroma of alcohol is produced when sugar is converted into alcohol by yeast.
• This transformation of sugar into alcohol is referred to as fermentation.
• Louis Pasteur made the discovery of fermentation in the year 1857.

Medicinal Use of Microorganisms

• Antibiotics prescribed by doctors, such as penicillin, are derived from microorganisms.
• These medicines are designed to kill or inhibit the growth of disease-causing microorganisms.
• Antibiotics are produced from bacteria and fungi, with streptomycin, tetracycline, and erythromycin being some examples.
• They are manufactured by cultivating specific microorganisms and are effective in treating various diseases.
• Antibiotics are administered to livestock and poultry through their feed to prevent microbial infections.
• They are also employed in controlling plant diseases.

Precautions Before Taking Antibiotics

• Antibiotics should only be taken under the guidance of a qualified doctor.
• It’s important to complete the full course of antibiotics as prescribed by the doctor.
• Misuse of antibiotics, such as taking them when not needed or in incorrect doses, can reduce their effectiveness in the future.
• Unnecessary use of antibiotics can also eliminate beneficial bacteria in the body.
• Antibiotics are ineffective against cold and flu since these illnesses are caused by viruses.

Vaccine

• When a disease-causing microbe enters the body, antibodies are produced to combat it.
• The body develops memory of how to fight the microbe for future encounters.
• Introducing dead or weakened microbes into a healthy body triggers the production of antibodies, providing immunity.
• Antibodies generated from vaccination remain in the body, offering long-term protection against disease-causing microbes.
• Vaccines prevent diseases such as cholera, tuberculosis, smallpox, and hepatitis by inducing immunity.
• Childhood vaccinations protect against various diseases.
• It’s crucial to immunize all children against these diseases, and vaccines are readily available in nearby hospitals.
• The Pulse Polio Programme aims to protect children against polio, with polio drops serving as a vaccine.
• Smallpox has been eradicated from most parts of the world due to a global campaign.
• Vaccines are produced on a large scale from microorganisms to safeguard humans and animals from numerous diseases.

Increasing Soil Fertility

• Certain bacteria have the capability to fix nitrogen from the atmosphere.
• This process enriches the soil with nitrogen and enhances its fertility.
• Bacteria that perform this function are known as biological nitrogen fixers.

Cleaning the Environment

• Microorganisms decompose dead organic matter like decaying plants and animals, converting them into simple substances that can be reused by other organisms.
• Microorganisms play a vital role in cleaning up the environment by degrading harmful and smelly substances.

Harmful Microorganisms

• Microorganisms can be harmful, causing diseases in humans, plants, and animals.
• Pathogens are microorganisms responsible for causing diseases.
• Certain microorganisms spoil food, clothing, and leather.

Disease causing Microorganisms in Humans

• Pathogens can enter the body through various means such as breathing air, drinking water, or consuming food.
• They can also be transmitted through direct contact with an infected person or carried by animals.
• Communicable diseases are microbial diseases that spread from an infected person to a healthy person through air, water, food, or physical contact.
• Examples of communicable diseases include cholera, the common cold, chickenpox, and tuberculosis.
• Some insects and animals, like the housefly, act as carriers of disease-causing microbes by picking up pathogens from garbage and animal excreta.
• When these flies land on uncovered food, they can transfer the pathogens, potentially causing illness in those who consume the contaminated food.
• It’s advisable to always keep food covered and avoid consuming uncovered items to prevent contamination.
• Female Anopheles mosquitoes are carriers of the malaria parasite (Plasmodium), while female Aedes mosquitoes transmit the dengue virus.
• Controlling the spread of malaria and dengue involves measures such as eliminating mosquito breeding sites, using mosquito nets, applying insect repellents, and implementing mosquito control programs.
• Mosquitoes breed in water, so it’s essential to prevent water from collecting in places like coolers, tires, and flower pots.
• Maintaining clean and dry surroundings helps prevent mosquitoes from breeding.
• Measures to avoid the spread of malaria include eliminating stagnant water, using mosquito nets, applying insect repellents, draining water from containers, and promoting awareness about mosquito breeding prevention.

Disease causing Microorganisms in Animals

• Various microorganisms can cause diseases in humans, plants, and animals.
• Anthrax, a dangerous disease affecting humans and cattle, is caused by a bacterium.
• Foot and mouth disease in cattle is caused by a virus.
• Robert Köch discovered Bacillus anthracis, the bacterium responsible for anthrax disease, in 1876.

Disease causing Microorganisms in Plants

• Various microorganisms cause diseases in plants, affecting crops like wheat, rice, potato, sugarcane, oranges, and apples.
• These diseases often lead to reduced crop yields.
• Plant diseases can be controlled using chemicals that kill the microbes responsible.
• Examples of plant diseases and their causative agents include citrus canker (bacteria, spread through air), rust of wheat (fungi, transmitted through air and seeds), and yellow vein mosaic of bhindi (virus, carried by insects).

Food Poisoning

• Food poisoning can result from consuming food contaminated by microorganisms.
• Microorganisms that grow on food can produce toxic substances, rendering the food poisonous and causing severe illness or death.
• Proper food preservation is crucial to prevent food spoilage and the risk of food poisoning.

Food Preservation

• Microorganisms can spoil food, causing it to emit a bad smell, develop a bad taste, and change color.
• Spoiling of food is associated with the activity of microorganisms and is not considered a chemical reaction.
• Paheli observed that some mangoes she bought spoiled after a few days, but her grandmother’s mango pickle remains preserved for a long time without spoiling.
• Paheli is confused about why the mango pickle does not spoil, despite being made from the same fruit that spoiled when she bought it.

Chemical Method

• Salts and edible oils are commonly used chemicals to inhibit the growth of microorganisms, making them effective preservatives.
• These preservatives, such as salt or acid, are added to pickles to prevent microbial attack.
• Sodium benzoate and sodium metabisulfite are examples of common preservatives used in pickles, jams, and squashes to prevent spoilage.

Preservation by Common Salt

• Common salt has been used for ages to preserve meat and fish.
• Meat and fish are coated with dry salt to inhibit the growth of bacteria.
• Salting is also employed to preserve fruits like amla, raw mangoes, and tamarind.

Preservation by Sugar

• Jams, jellies, and squashes are preserved using sugar.
• Sugar lowers the moisture content, thereby inhibiting the growth of bacteria that spoil food.

Preservation by Oil and Vinegar

• Oil and vinegar are utilized to prevent spoilage of pickles because bacteria cannot thrive in such an environment.
• This preservation method is commonly used for preserving vegetables, fruits, fish, and meat.

Heat and Cold Treatments

• Boiling milk before storage or use is a common practice because it kills many microorganisms.
• Refrigeration is employed to preserve food as low temperatures inhibit the growth of microbes.
• Pasteurized milk is safe to consume without boiling as it is free from harmful microbes.
• The milk is heated to around 70°C for 15 to 30 seconds, then rapidly chilled and stored, preventing microbial growth.
• Louis Pasteur discovered this process, known as pasteurization.

Storage and Packing

• Dry fruits and vegetables are now often sold in sealed, airtight packets.
• Sealed packaging helps prevent the growth of microbes and preserves the quality of the products.

Nitrogen Fixation

• Rhizobium bacteria are involved in nitrogen fixation in leguminous plants like pulses.
• Rhizobium forms a symbiotic relationship with leguminous plants and resides in the root nodules.
• While nitrogen fixation can also occur through lightning, the overall amount of nitrogen in the atmosphere remains constant.

Nitrogen Cycle

• The atmosphere contains 78% nitrogen gas.
• Nitrogen is vital for all living organisms, forming part of proteins, chlorophyll, nucleic acids, and vitamins.
• Plants and animals cannot directly utilize atmospheric nitrogen.
• Certain bacteria and blue-green algae in the soil fix atmospheric nitrogen, converting it into usable compounds.
• Plants absorb these nitrogen compounds from the soil through their roots and use them to synthesize proteins and other compounds.
• Animals obtain these proteins and nitrogen compounds by feeding on plants.
• When plants and animals die, bacteria and fungi in the soil convert nitrogenous wastes into nitrogenous compounds.
• These compounds are reused by plants.
• Some bacteria convert a portion of these compounds into nitrogen gas, which returns to the atmosphere.
• This process helps maintain the constant percentage of nitrogen in the atmosphere.