Test: Microorganisms : Friend Or Foe - 2 - Class 8 MCQ

Explanation of Correct Answer

The correct answer is Decomposition. This process involves microorganisms breaking down organic waste, such as dead plants and animals, into simpler, harmless substances. These microorganisms play a crucial role in recycling nutrients back into the ecosystem.

Explanation of Incorrect Options

• Photosynthesis: This is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll. It does not involve breaking down organic waste.
• Nitrogen fixation: This refers to the conversion of atmospheric nitrogen into a form usable by plants, primarily carried out by certain bacteria. It does not involve the breakdown of organic waste.
• Fermentation: This is a metabolic process that converts sugar to acids, gases, or alcohol in the absence of oxygen. While it involves microorganisms, it does not specifically refer to the breakdown of organic waste into harmless substances.

Explanation of Correct Answer

The correct answer is Influenza, which is a viral infection that affects the respiratory system. It is caused by the influenza virus and is known for its symptoms such as fever, cough, and body aches.

Explanation of Incorrect Options

• Typhoid: This disease is caused by the bacterium Salmonella typhi, not a virus.
• Dysentery: This condition is primarily caused by bacteria (such as Shigella) or parasites, not a virus.
• Cholera: Cholera is caused by the bacterium Vibrio cholerae, which leads to severe diarrhoea and dehydration.

Explanation of Correct Answer

The correct answer is All of the above. Each of the options listed is a common preservative used in kitchens to prevent spoilage due to microbial infection:

• Vinegar: Its acidic nature inhibits the growth of bacteria and is commonly used in pickling.
• Common salt: Salt draws moisture out of food, creating an environment that is inhospitable to bacteria.
• Oil: Oil can create a barrier that prevents air from reaching food, thus slowing down spoilage.

Explanation of Incorrect Options

• Vinegar: While vinegar is a preservative, it is not the only one, making this option incomplete.
• Common salt: Similar to vinegar, common salt is effective but does not encompass all methods of preservation.
• Oil: Oil alone does not cover all preservation methods, thus making it an insufficient answer.

Yeast plays a crucial role in baking through the process of fermentation. The correct answer is both A and B because:

• It turns sugar into alcohol: During fermentation, yeast converts sugars into alcohol and carbon dioxide.
• It produces carbon dioxide, causing dough to rise: The carbon dioxide produced during fermentation creates bubbles in the dough, causing it to rise.

Now, let's examine the incorrect options:

• Option A is partially correct but does not encompass the full role of yeast in baking, which also includes the production of carbon dioxide.
• Option B is also correct by itself, but it does not mention the alcohol production aspect.
• Option D is incorrect because while yeast can decompose organic matter, its primary role in baking is related to fermentation for leavening dough.

The correct answer is Lactobacillus, which is a type of bacteria that ferments lactose, the sugar found in milk, to produce lactic acid. This process thickens the milk and turns it into curd.

Explanation of Incorrect Options

• Yeast: While yeast is used in the fermentation of sugars to produce alcohol and carbon dioxide, it is not responsible for turning milk into curd.
• Penicillin: This is an antibiotic derived from the Penicillium fungus and is used to treat bacterial infections, not for curd production.
• Streptomycin: Similar to penicillin, streptomycin is an antibiotic used to treat infections and has no role in the fermentation of milk into curd.

Bacteria and fungi are the primary microorganisms used in the preparation of antibiotics. Antibiotics are substances that kill or inhibit the growth of bacteria and are often derived from these microorganisms.

Explanation of Incorrect Options

• Viruses: Viruses are not used in the production of antibiotics. They require a host to replicate and are not classified as living organisms.
• Algae: While algae have various uses, they are not typically involved in the production of antibiotics.
• Protozoa: Protozoa are single-celled organisms that can cause diseases but are not used to produce antibiotics.

When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes for ever. This is how a vaccine works.

Explanation of Correct Answer

The correct answer is Antibodies because they are specifically produced by the immune system to identify and neutralise pathogens such as bacteria and viruses.

Explanation of Incorrect Options

• Enzymes: While enzymes play various roles in the body, they are not specifically produced to fight microbes.
• Hormones: Hormones regulate various physiological processes but do not directly combat disease-carrying microbes.
• Proteins: Although antibodies are proteins, not all proteins produced by the body are involved in fighting diseases.

Fungus is the microorganism responsible for producing penicillin. Specifically, the mould Penicillium notatum was discovered by Alexander Fleming to have antibiotic properties that inhibit bacterial growth.

Explanation of Incorrect Options

• Bacteria: While some bacteria produce antibiotics, they are not responsible for penicillin production.
• Yeast: Yeast is primarily used in fermentation processes, such as baking and brewing, but it does not produce penicillin.
• Protozoa: Protozoa are single-celled organisms that can cause diseases but do not produce antibiotics like penicillin.

When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes for ever. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox, and hepatitis can be prevented by vaccination.

Explanation of Correct Answer

The correct answer is C. To stimulate the body to produce antibodies. Introducing dead or weakened microbes into the body helps to train the immune system to recognise and combat the actual pathogens without causing the disease.

Explanation of Incorrect Options

• A. To create a new infection: This is incorrect because the purpose of introducing dead or weakened microbes is to prevent infection, not to create one.
• B. To allow microbes to multiply: This is incorrect as the introduction of dead or weakened microbes does not allow them to multiply; instead, it stimulates an immune response.
• D. To weaken the immune system: This is incorrect because the introduction of dead or weakened microbes actually strengthens the immune system by helping it to learn how to fight off future infections.

Edward Jenner discovered the vaccine for smallpox in 1798. His work laid the foundation for immunology and the development of vaccines.

Explanation of Incorrect Options

• Polio: The vaccine for polio was developed by Jonas Salk and Albert Sabin in the 20th century, long after Jenner's discovery.
• Measles: The measles vaccine was developed in the 1960s by John Enders and his colleagues, not by Jenner.
• Tuberculosis: The vaccine for tuberculosis, known as the BCG vaccine, was developed in the early 20th century by Albert Calmette and Camille Guérin.