All questions of Microorganisms : Friend or Foe for Class 8 Exam

Explanation:

Tuberculosis:
- Tuberculosis is a disease caused by the bacterium Mycobacterium tuberculosis.
- It primarily affects the lungs but can also affect other parts of the body.
- The disease is spread through the air when an infected person coughs or sneezes, releasing bacteria into the air.
- People nearby can then breathe in these bacteria and become infected.
- Tuberculosis is a highly contagious disease, especially in crowded or poorly ventilated environments.
- Symptoms of tuberculosis include coughing, chest pain, weight loss, fatigue, and fever.
- Treatment usually involves a combination of antibiotics taken over several months to kill the bacteria in the body.
- Without treatment, tuberculosis can be deadly, but with proper medical intervention, most people can be cured.

Therefore, tuberculosis is the correct answer as it is a disease spread due to bacteria.

Role of Yeast in Baking
Yeast is a vital ingredient in baking, primarily serving to leaven dough, which is essential for creating light and airy baked goods.
How Yeast Works
- Yeast is a living microorganism that belongs to the fungus kingdom.
- When mixed with flour and water, yeast begins to feed on the sugars present in the dough.
Fermentation Process
- As yeast consumes sugar, it undergoes a process called fermentation.
- During fermentation, yeast converts sugar into carbon dioxide and alcohol.
Carbon Dioxide Production
- The carbon dioxide gas produced is what causes the dough to rise.
- As the gas gets trapped in the dough’s gluten structure, it expands and creates air pockets.
Importance of Rising Dough
- The rise in dough is crucial for the texture and volume of baked products like bread, rolls, and pastries.
- Without yeast, dough would remain flat and dense, resulting in a heavy final product.
Conclusion
- While yeast does turn sugar into alcohol, its primary role in baking is the production of carbon dioxide.
- Thus, the correct answer to the question is option 'B': it produces carbon dioxide, causing dough to rise, making yeast an essential component in the baking process.

Dengue fever is spread by mosquitoes, so preventing mosquito bites using mosquito nets and repellents is crucial for controlling the disease.

Decomposition is the process where microorganisms break down organic waste (like vegetable peels and animal remains) into harmless and usable substances.

Antibiotics are produced from bacteria and fungi. They are used to treat bacterial infections by inhibiting or killing the bacteria.

Preventing the growth of bacteria:
Using common salt to preserve meat and fish serves the main purpose of preventing the growth of bacteria. Salt creates a high-salt environment that is inhospitable to most bacteria, thus slowing down the process of bacterial growth and spoilage.

How salt preserves meat and fish:
- When salt is applied to the surface of meat or fish, it draws out moisture through the process of osmosis.
- This dehydration inhibits the growth of bacteria, as they require moisture to thrive.
- The high salt concentration also creates a hypertonic environment that further limits the growth of bacteria.

Benefits of using salt as a preservative:
- By inhibiting bacterial growth, salt helps extend the shelf life of meat and fish.
- It allows for long-term storage without the need for refrigeration, making it a practical method of preservation in the absence of modern refrigeration technology.

Other uses of salt in food preservation:
- In addition to preventing bacterial growth, salt also enhances flavor and helps in the curing process of meat and fish.
- It can also contribute to the texture and tenderness of preserved foods.
In conclusion, the main purpose of using common salt to preserve meat and fish is to prevent the growth of bacteria, thereby extending the shelf life of these perishable food items.

Tuberculosis is a communicable disease that spreads through the air from an infected person to a healthy person. It is different from non-communicable diseases like diabetes and cancer.

Understanding the Purpose of Introducing Dead or Weakened Microbes
The introduction of dead or weakened microbes into the body is a fundamental principle of vaccination. Here's a detailed explanation of why this practice is essential in immunology.
Stimulating Immune Response
- When dead or weakened microbes are introduced, they do not cause disease.
- Instead, they act as antigens, which are substances that provoke an immune response.
Production of Antibodies
- The immune system recognizes these antigens as foreign invaders.
- In response, the body produces specific proteins called antibodies.
- These antibodies are crucial because they can recognize and neutralize the actual pathogens if encountered in the future.
Building Immunity
- This process helps the body develop immunity without experiencing the actual disease.
- If the body is later exposed to the live pathogen, it can respond quickly and effectively using the antibodies and memory cells generated during vaccination.
Long-term Protection
- Vaccination not only protects the individual but also contributes to herd immunity in the community.
- When a significant portion of the population is immunized, the spread of the disease is reduced, protecting those who cannot be vaccinated.
In conclusion, introducing dead or weakened microbes into the body primarily serves to stimulate the production of antibodies, thus preparing the immune system to fight off future infections effectively. This proactive approach is a cornerstone of public health and disease prevention.

Yeast is used for the production of alcohol and wine by a process known as fermentation.
When yeast is added to sugar solution, it causes fermentation and forms alcohol.

Understanding Food Preservation
Food preservation is essential for extending the shelf life of food products and preventing spoilage due to microbial activity. Several common kitchen ingredients serve as effective preservatives.
1. Vinegar
- Vinegar is an acidic substance that creates an environment unsuitable for many bacteria and molds.
- It is commonly used in pickling vegetables, which helps to enhance flavor and prolong shelf life.
2. Common Salt
- Salt is one of the oldest and most effective preservatives.
- It works by drawing moisture out of food through a process called osmosis, making it difficult for microbes to thrive.
- Salt is frequently used in curing meats and preserving fish.
3. Oil
- Oil acts as a barrier to oxygen, which can promote spoilage and rancidity.
- By creating an anaerobic environment, oil helps to inhibit the growth of bacteria and molds.
- It is commonly used in marinades and preserving foods like olives and sun-dried tomatoes.
4. All of the Above
- Each of these substances—vinegar, common salt, and oil—plays a unique role in food preservation.
- They can be used individually or in combination to enhance the longevity and safety of food products.
In conclusion, all these ingredients are valuable in the kitchen for preventing spoilage and ensuring that food remains safe for consumption over extended periods. Therefore, the correct answer is option 'D' – all of the above.

- The bacterium responsible for curd formation is Lactobacillus.
- It is a type of lactic acid bacteria that ferments lactose, the sugar found in milk.
- This fermentation process produces lactic acid, which causes the milk to thicken and transform into curd.
- Lactobacillus thrives at temperatures between 30 to 40°C, making it ideal for curd production.
- Other options like Salmonella typhi and Vibrio cholera are harmful bacteria, while Penicillin is a fungus, not a bacterium.

Understanding Nitrogen Conversion by Soil Bacteria
Soil bacteria play a crucial role in the nitrogen cycle, a vital process for maintaining the ecosystem's health. One of the key transformations they facilitate is the conversion of nitrogen compounds into nitrogen gas (N2).
What is Nitrogen Gas?
- Nitrogen gas is a diatomic molecule (N2) that makes up about 78% of Earth's atmosphere.
- It is non-reactive and cannot be used directly by most living organisms.
Role of Soil Bacteria
- Certain soil bacteria, particularly those involved in denitrification, convert nitrogen compounds like nitrates (NO3-) and nitrites (NO2-) into nitrogen gas.
- This process occurs primarily in anaerobic conditions (low oxygen environments), often found in waterlogged soils.
Steps in the Process
- Nitrate Reduction: Bacteria, such as Pseudomonas and Bacillus species, take up nitrates and nitrites.
- Denitrification: Through a series of enzymatic reactions, these compounds are reduced, ultimately releasing nitrogen gas back into the atmosphere.
Importance of Denitrification
- Helps maintain the nitrogen balance in the soil.
- Prevents the accumulation of excess nitrates which can lead to environmental issues, such as water pollution and eutrophication.
Conclusion
In summary, soil bacteria convert nitrogen compounds into nitrogen gas through denitrification, playing a critical role in the nitrogen cycle and contributing to the overall health of ecosystems. This transformation not only recycles nutrients but also helps maintain atmospheric nitrogen levels, ensuring a balanced environment for all living organisms.

Certain bacteria fix nitrogen from the atmosphere into the soil, making it available as a nutrient for plants. This process is essential for maintaining soil fertility and supporting plant growth.

Role of Lactobacillus in Food Production
Lactobacillus is a vital bacterium in the food industry, particularly in the fermentation process. Its primary role is in the transformation of milk into curd, making it essential for various dairy products.
How Lactobacillus Works
• Lactobacillus ferments lactose, the sugar found in milk.
• During fermentation, it produces lactic acid, which is crucial for curd formation.
• The increase in acidity caused by lactic acid causes milk proteins (casein) to coagulate, resulting in curd.
Importance in Dairy Products
• Curd is the base for various dairy products such as yogurt, cheese, and buttermilk.
• The fermentation process not only enhances flavor but also improves the nutritional value of these products.
• Lactobacillus helps in preserving food by preventing spoilage and inhibiting harmful bacteria.
Health Benefits
• Besides its role in food production, Lactobacillus is known for its probiotic properties.
• It aids digestion and can improve gut health when consumed.
• Regular consumption of products containing Lactobacillus may enhance the immune system.
Conclusion
In summary, Lactobacillus plays a crucial role in converting milk into curd through fermentation, making it indispensable in the production of various dairy products. Its ability to produce lactic acid not only aids in curd formation but also enhances the flavor, nutritional value, and shelf life of food.

Understanding Antibiotics
Antibiotics are vital tools in modern medicine used to combat bacterial infections. They work by targeting specific features of bacteria, which allows them to effectively kill or inhibit the growth of these pathogens.
Why Antibiotics Target Bacteria
- Bacterial Infections: Antibiotics are specifically designed to treat infections caused by bacteria, such as strep throat, urinary tract infections, and pneumonia.
- Mechanism of Action: They function by disrupting vital processes in bacterial cells, such as:
- Cell Wall Synthesis: Some antibiotics prevent bacteria from forming strong cell walls, leading to cell lysis and death.
- Protein Synthesis: Others inhibit the machinery that bacteria use to produce proteins necessary for their growth and reproduction.
- DNA Replication: Certain antibiotics interfere with the bacteria's ability to replicate their DNA.
Other Pathogens
- Viruses: Unlike bacteria, viruses are not affected by antibiotics. Conditions like the common cold or influenza are caused by viruses, which require antiviral medications for treatment.
- Fungi and Parasites: Similarly, fungal infections (like athlete's foot) and parasitic infections (such as malaria) are treated with antifungal and antiparasitic medications, respectively, and not antibiotics.
Conclusion
In summary, the correct answer to the question is option 'A' because antibiotics are specifically effective against bacteria, not viruses, fungi, or parasites. Understanding this distinction is crucial for effective treatment and to avoid the misuse of antibiotics, which can lead to antibiotic resistance.

Role of Microorganisms in Root Nodules
Leguminous plants, such as peas, beans, and clover, form a symbiotic relationship with certain microorganisms, primarily rhizobia, within their root nodules. This interaction is crucial for nitrogen fixation, a vital process for soil fertility and plant growth.
What is Nitrogen Fixation?
- Nitrogen fixation is the conversion of atmospheric nitrogen (N2) into ammonia (NH3) or related compounds.
- This process is essential because most plants cannot utilize atmospheric nitrogen directly.
Function of Rhizobia
- Rhizobia are soil bacteria that infect the root hairs of leguminous plants.
- Upon infection, they stimulate the formation of root nodules, where they reside and multiply.
How Nitrogen Fixation Occurs
- Inside the root nodules, rhizobia convert nitrogen gas from the atmosphere into ammonia.
- This ammonia is then used by the plant to synthesize proteins and other essential compounds.
Benefits to the Ecosystem
- The fixed nitrogen enriches the soil, making it more fertile for subsequent crops.
- This process reduces the need for synthetic nitrogen fertilizers, promoting sustainable agriculture.
Conclusion
The microorganisms in the root nodules of leguminous plants play a critical role in fixing nitrogen from the air into the soil, benefiting both the plants and the broader ecosystem. This symbiotic relationship is a key aspect of nutrient cycling in agricultural systems.

Protozoans
Protozoans are single-celled microorganisms that can cause serious diseases in humans. Two common examples of protozoans that cause serious diseases are:
- Dysentery: Dysentery is a gastrointestinal infection that causes inflammation of the intestines, leading to symptoms such as diarrhea, abdominal pain, and fever. The protozoan parasite Entamoeba histolytica is known to cause amoebic dysentery, which can be life-threatening if left untreated.
- Malaria: Malaria is a deadly disease caused by the Plasmodium parasite, which is transmitted to humans through the bite of infected mosquitoes. The parasite multiplies in the liver and red blood cells, leading to symptoms such as fever, chills, and anemia. If not treated promptly, malaria can result in severe complications and even death.
Protozoans are responsible for a range of other diseases as well, highlighting the importance of preventive measures such as proper sanitation, clean water sources, and vector control to reduce the transmission of these harmful microorganisms.

When microorganisms grow on food, they can cause food poisoning. These microorganisms may produce toxins or contaminate the food, leading to gastrointestinal illnesses.

Anthrax is caused by the bacterium Bacillus anthracis. It affects both humans and animals, especially cattle.

Penicillin Production by Mould
The microorganism responsible for producing penicillin is mould. Let's delve into the details of how mould plays a crucial role in the production of this widely used antibiotic.
Benefits of Mould in Penicillin Production:
- **Penicillin Production**: Mould, specifically Penicillium fungi, naturally produce penicillin as part of their defense mechanism against bacteria. This antibiotic helps the mould to outcompete other microorganisms in its environment.
- **Antibacterial Properties**: Penicillin is effective against a wide range of bacteria, making it a valuable weapon in fighting various infections in humans.
Process of Penicillin Production:
- **Fermentation**: The penicillin production process involves fermenting Penicillium fungi in large-scale bioreactors. These controlled environments provide optimal conditions for mould growth and penicillin production.
- **Extraction**: Once the mould has produced a sufficient amount of penicillin, the antibiotic is extracted from the fermentation broth through a series of purification steps.
- **Purification**: The extracted penicillin undergoes purification to remove impurities and obtain a highly concentrated form of the antibiotic suitable for medical use.
Role of Mould in Medicine:
- **Medical Applications**: Penicillin revolutionized the field of medicine by providing an effective treatment for bacterial infections. It has saved countless lives since its discovery.
- **Development of Antibiotics**: The success of penicillin paved the way for the development of other antibiotics, expanding the arsenal of treatments available to combat infectious diseases.
In conclusion, mould, specifically Penicillium fungi, is the key microorganism responsible for producing penicillin. Its natural ability to synthesize this important antibiotic has had a profound impact on medicine and human health.