Microorganisms - Class 8 Notes & Olympiad Questions

Microorganisms

Microorganisms, also known as microbes, are tiny living organisms that are too small to be seen with the naked eye. They exist all around us, in the air we breathe, the water we drink, and even inside our bodies. Despite their small size, they play incredibly important roles in the natural world and in our lives.

Microorganisms come in different types, and the main groups include bacteria, fungi, protozoa, some algae, and viruses.

1. Bacteria

Characteristics of Bacteria

a) Bacteria are single-celled microorganisms with a simple structure.
b) They have a unique structure, which includes a rigid cell wall, and belong to a group called "Monera."
c) They can be found in various shapes, including cocci (spherical), bacilli (rod-shaped), Vibrio (comma-shaped) and spirilla (spiral-shaped).
d) Bacteria can move using flagella (whip-like structures) or by gliding.

Habitat of Bacteria

a) Bacteria inhabit diverse environments, ranging from soil and water to extreme conditions like hot springs and ice.
b) They can be found in the air, on surfaces, and even inside the bodies of animals and humans.
c) Some bacteria are specialised for specific habitats, while others are generalists and can thrive in various conditions.

Reproduction in Bacteria

a) One of the most intriguing aspects of bacteria is their ability to multiply through a process called fission.
b) In fission, a single bacterial cell divides into two identical daughter cells.
c) This remarkable reproductive capability allows bacteria to grow and multiply rapidly, leading to the formation of colonies.

Nutrition in Bacteria

a) Bacteria exhibit diverse nutritional strategies. Some are autotrophs, which can produce their food through photosynthesis (using sunlight) or chemosynthesis (using chemical energy).
b) Others are heterotrophs, which obtain nutrients by consuming organic matter or other organisms.
c) Saprophytic bacteria decompose dead organic material and recycle nutrients back into the ecosystem.
d) Parasitic bacteria obtain nutrients from living hosts, often causing diseases in the process.

Examples: Escherichia coli (E. coli), Streptococcus pyogenes, Bacillus subtilis.

2. Fungi

Characteristics of Fungi

a) Fungi are unique and intriguing microorganisms that belong to their own special group called the Kingdom Fungi.
b) Unlike plants, they cannot make their food through photosynthesis because they lack chlorophyll.
c) Fungi play essential roles in ecosystems as decomposers, helping to break down dead organic matter and recycle nutrients.

Unicellular and Multicellular Fungi

a) Fungi come in different forms. Some, like yeast, are unicellular, meaning they are made up of a single cell.
b) Others, like the moulds you might find on old bread, are multicellular, composed of many interconnected cells.

Reproduction in Fungi

a) Fungi have diverse methods of reproduction. Some fungi, like yeast, reproduce by a process called budding, where a small part of the parent cell grows into a new cell.
b) Others, like bread moulds, can reproduce by breaking into fragments, each of which can grow into a new fungus.
c) Another common way for fungi to reproduce is by producing tiny, lightweight spores that can travel far and wide to start new colonies.

Nutrition in Fungi

a) Some fungi are saprophytic, which means they feed on dead and decaying matter.
b) Others are heterotrophic, meaning they obtain their nutrients by absorbing them from other living organisms.
c) There are also parasitic fungi, which get their nutrition by living on or inside a host organism and causing harm to it.

Examples: Saccharomyces cerevisiae, Penicillium notatum.

3. Algae

Characteristics of Algae

a) Algae are microorganisms that can be found in various water bodies like ponds, rivers, and even oceans. Although they might look like tiny plants, they have some unique characteristics that set them apart.
b) One of the key features of algae is that they contain chlorophyll, a pigment that helps them perform photosynthesis, just like plants do. Additionally, algae have a protective cell wall that gives them structure and support.
c) Although algae share similarities with plants, they differ in some essential ways. Unlike traditional plants, algae lack proper roots, stems, and leaves. Instead, they have simple structures that allow them to thrive in water environments.

Unicellular and Multicellular Algae

a) Algae come in different forms. Some are unicellular, meaning they consist of a single cell. For example, Chlamydomonas is a unicellular algae.
b) On the other hand, some algae are multicellular, like Spirogyra, composed of many interconnected cells. This variety makes algae a diverse group of microorganisms.

Reproduction in Algae

a) Algae have several methods of reproduction. They can reproduce by fragmentation, where a part of the algae breaks off and grows into a new individual.
b) Another method is fission, where the cell divides into two identical daughter cells.
c) Additionally, some algae produce tiny reproductive units called spores, which can disperse and grow into new algae.

Nutrition in Algae

a) Algae are amazing organisms as they can prepare their food through photosynthesis, just like plants.
b) They use sunlight, water, and carbon dioxide to produce their nutrients, playing a critical role in aquatic ecosystems and contributing to the oxygen we breathe.

Examples: Chlamydomonas, Spirogyra.

4. Protozoa

Characteristics of Protozoa

a) Protozoa are remarkable microscopic creatures that live as single-celled organisms.
b) Despite their small size, they exhibit diverse behaviours and play essential roles in various aquatic environments.

Habitat of Protozoa

a) Most protozoa prefer living in water and can be found in freshwater bodies like lakes, rivers, and ponds, as well as in salty marine waters.
b) They also inhabit the soil in moist environments, contributing to the complexity of the ecosystems they inhabit.

Reproduction in Protozoa

a) As single-celled organisms, protozoa reproduce asexually through fission which involves the cell splitting into two identical daughter cells.
b) Budding is another method, where a small outgrowth develops on the parent cell and eventually separates to become a new individual.
c) Some protozoa also produce spores, specialized cells that can develop into new protozoa under suitable conditions.

Nutrition in Protozoa

a) Protozoa display different ways of obtaining nutrition. Some are holozoic, meaning they consume tiny organisms or particles in their environment.
b) Others are parasitic, relying on other organisms for their sustenance.
c) Additionally, some protozoa are saprophytic, feeding on dead organic matter, helping in the decomposition process.

Examples: Amoeba, Paramecium.

5. Viruses

Characteristics of Viruses

a) Viruses are incredibly small microorganisms, even tinier than any known cell. Viruses exhibit characteristics of both living and non-living.
b) They lack many essential features of living organisms, such as the ability to carry out metabolism or grow independently. However, once they infect a host cell, they exhibit characteristics of life, like reproducing and evolving.

Reproduction in Viruses

a) Viruses have a peculiar way of multiplying. Unlike other living organisms, they cannot reproduce on their own.
b) Instead, they need to invade the cells of a host organism to replicate. Once inside, they hijack the host's cellular machinery to create copies of themselves, leading to infection and potential harm to the host.

Examples: Influenza virus, Human Immunodeficiency Virus (HIV), Bacteriophage.

Microorganisms' Impact on Humans and the Environment

Beneficial Effects of Microbes

Microbes, or microorganisms, have numerous beneficial uses that positively impact our daily lives and various industries.

1. Food Production

a) Fermentation: Microbes like yeast are used to ferment dough in baking, producing bread and pastries. They also ferment sugars to create alcohol in the brewing of beer and wine.

b) Dairy Products: Bacteria are essential in making yoghurt, cheese, and other dairy products. For example, Lactobacillus bacteria convert milk into yoghurt through fermentation.

2. Medicine and Vaccines

a) Antibiotics: Antibiotics are medicines that come from microorganisms and are designed to kill or inhibit the growth of disease-causing microbes in our bodies. Microbes like Penicillium fungi produce antibiotics like penicillin, which help in treating bacterial infections and saving millions of lives.
Some well-known antibiotics are streptomycin, tetracycline, and erythromycin.

b) Vaccines: When disease-causing microbes enter our body, our immune system produces antibodies to fight them off and protect us from future infections. Vaccination is a way to introduce weakened or killed microbes into our bodies, prompting our immune system to develop antibodies without causing the actual disease. For instance, the measles vaccine is made using a weakened measles virus.
Vaccines protect against several diseases like polio, measles, mumps, rubella, hepatitis, and more.

3. Agriculture

a) Nitrogen Fixation: Certain bacteria, such as Rhizobium, convert atmospheric nitrogen into a usable form for leguminous plants like peas and beans and enhance soil fertility.

b) Biofertilizers: Microbes in biofertilizers improve soil health and nutrient availability to plants, promoting better crop yields.

4. Environmental Cleanup

a) Bioremediation: Microbes are employed to clean up oil spills and break down harmful pollutants in the environment, helping to restore natural ecosystems.

b) Composting: Microbes facilitate the decomposition of organic waste in compost piles, producing nutrient-rich compost for gardening.

5. Waste Treatment

Sewage Treatment: Microbes are employed in wastewater treatment plants to break down organic matter and purify water before it is released back into the environment.

Harmful Effects of Microbes

1. Food Spoilage: Certain microbes can spoil our food, making it unsafe for consumption. Bacteria and moulds can grow on food items like bread, fruits, and vegetables, producing toxins and causing bad odours and flavours. Food poisoning is a common example of harmful effects caused by microbial contamination.

2. Decay and Rot: Microbes play a role in the decay and decomposition of organic matter. They break down dead plants, animals, and other organic materials, leading to the release of foul-smelling gases and substances. For instance, the fungus on rotting wood is an example of microbial decomposition.

3. Water Contamination: Microbes can contaminate water sources and lead to waterborne diseases like cholera and dysentery. Bacteria, viruses, and parasites are often responsible for such waterborne illnesses.

4. Infectious Diseases: Microbes can cause various infectious diseases in humans, and animals. These diseases can range from common illnesses like the flu and cold to more severe ones like tuberculosis, cholera, and malaria. For example, the influenza virus causes seasonal flu, which can spread rapidly and lead to respiratory complications.

Some Common Human Diseases caused by Microorganisms

Animal Diseases Caused by Microorganisms

5. Plant Diseases: Microbes, especially fungi and bacteria, can cause diseases in plants, leading to reduced crop yields and economic losses for farmers. Examples include wheat rust, which affects wheat crops, and potato blight, which affects potato plants.

Plant Diseases Caused by Microorganisms

Food Preservation

Food preservation is essential to prevent the spoilage of food and increase its shelf life. Various methods are used to preserve different types of food.
Some common methods of food preservation are:

1. Heating: Heating is a common method used to preserve food. By subjecting food to high temperatures, microorganisms present in the food are killed, preventing their growth and spoilage. Canning and pasteurization are examples of heat-based preservation methods.

2. Cooling (Refrigeration): Refrigeration involves storing food at low temperatures, typically in a refrigerator or freezer. Cold temperatures slow down the growth of microorganisms, keeping the food fresh for a longer time.

3. Pasteurization of Milk: Pasteurization is a process where milk is heated to a specific temperature to kill harmful bacteria, making the milk safe for consumption while retaining its nutritional value.

4. Drying or Dehydration: Drying or dehydration involves removing the moisture content from food, making it less hospitable for microorganisms to grow. Dried fruits, vegetables, and meat are common examples of dehydrated food.

5. Addition of Common Salt: Salt is a natural preservative that inhibits the growth of bacteria, yeasts, and moulds. Salting is used to preserve meat, fish, and some vegetables.

6. Addition of Sugar: Sugar acts as a preservative by creating an environment with low water activity, making it difficult for microorganisms to survive. Jams, jellies, and candies are preserved using sugar.

7. Canning: Canning involves sealing food in airtight containers and heating them to destroy microorganisms. This method helps preserve a wide range of foods, including fruits, vegetables, and soups.

Each preservation method has its advantages and is suitable for different types of food. These techniques have been used for centuries to ensure the availability of safe and nutritious food for extended periods.

Nitrogen Cycle

The nitrogen cycle is a crucial process that converts the nitrogen gas present in the atmosphere into forms that are usable by living organisms. It helps maintain a stable amount of nitrogen in the atmosphere, which is essential for life on Earth.

Steps in the Nitrogen Cycle

1. Nitrogen Fixation: Nitrogen fixation is the first step in the cycle. Lightning and certain bacteria in the soil have the ability to convert atmospheric nitrogen gas into nitrogen compounds. These compounds include ammonia and other nitrogen-containing molecules.

2. Nitrification: In the nitrification step, specific bacteria in the soil convert ammonia into nitrates. Nitrates are essential nutrients that plants can absorb through their roots. Plants use these nitrogen compounds to build proteins and other essential molecules.

3. Assimilation: During assimilation, plants take in the nitrogen compounds, such as nitrates, from the soil through their root system. They utilize these compounds to synthesize proteins and other important substances. Animals obtain their nitrogen by consuming plants or other animals that have already assimilated nitrogen.

4. Ammonification: When plants and animals die, their nitrogen-containing wastes and organic matter are broken down by bacteria and fungi in the soil. This process, known as ammonification, converts the organic nitrogen back into ammonia and other nitrogen compounds.

5. Denitrification: The final step of the nitrogen cycle is denitrification. Certain bacteria perform denitrification in environments with little or no oxygen. During this step, nitrates are converted back into gaseous nitrogen, which is released back into the atmosphere.

The nitrogen cycle is a continuous process that ensures a balance of nitrogen in the atmosphere and provides essential nutrients for plants and animals. It plays a vital role in sustaining life on Earth by making nitrogen available for the growth and development of living organisms.