CBSE – Grade 8 – Science – Ch 02 – QA

Question 1: Explain the observation of moist bread during the rainy season and the appearance of greyish white patches. What are the tiny, black rounded structures observed, and where do they come from?

Answer: During the rainy season, moist bread tends to spoil, and its surface gets covered with greyish white patches. By observing these patches through a magnifying glass, one can see tiny, black rounded structures known as mold. Mold originates from airborne spores that settle on the moist bread, germinate, and grow into the visible structures we observe.

Question 2: Provide a detailed classification of microorganisms mentioned in the text. What are the four major groups, and can you name some common microorganisms from each group?

Answer: Microorganisms are classified into four major groups: bacteria, fungi, protozoa, and some algae. Some common microorganisms include Escherichia coli (bacteria), Candida albicans (fungi), Amoeba proteus (protozoa), and Chlorella (algae).

Question 3: Describe the distinguishing features of viruses and how they cause diseases. Provide examples of both common ailments and serious diseases caused by viruses.

Answer: Viruses are microscopic entities that reproduce only inside the cells of a host organism. Common ailments like cold, influenza (flu), and most coughs are caused by viruses. Serious diseases such as polio and chickenpox also result from viral infections. The viruses hijack the host cell’s machinery for replication, leading to the manifestation of these diseases.

Question 4: Explain the environmental habitats where microorganisms can be found. Discuss the range of environments from cold climates to marshy lands, and highlight their presence inside the bodies of animals, including humans.

Answer: Microorganisms inhabit diverse environments, ranging from ice-cold climates to hot springs, deserts to marshy lands. They are also found inside the bodies of animals, including humans. Some microorganisms grow on other organisms as parasites, while others exist freely in the environment.

Question 5: Elaborate on the role of microorganisms in our lives, discussing both their beneficial and harmful aspects. Provide examples of beneficial and harmful microorganisms mentioned in the text.

Answer: Microorganisms play a crucial role in our lives. Beneficial microorganisms are used in the preparation of curd, bread, cake, and the production of alcohol. They aid in cleaning up the environment by breaking down organic wastes. Harmful microorganisms cause diseases like dysentery and malaria. The text emphasizes the dual nature of microorganisms—some beneficial, others harmful.

Question 6: Explore the uses of microorganisms in agriculture, focusing on how they contribute to increasing soil fertility. Mention specific examples of microorganisms and their roles in this context.

Answer: Microorganisms, particularly bacteria, are used in agriculture to increase soil fertility. Bacteria fix nitrogen, converting atmospheric nitrogen into a form usable by plants. This enhances soil fertility, promoting better plant growth. The text suggests that microorganisms play a vital role in sustainable agriculture practices.

Question 7: Discuss the role of Lactobacillus in the making of curd. Explain the process of how this bacterium promotes the formation of curd and its involvement in other food items.

Answer: Lactobacillus is a bacterium that plays a crucial role in the formation of curd. It multiplies in milk and converts it into curd through the process of fermentation. Additionally, Lactobacillus is involved in the making of cheese, pickles, and various other food items, showcasing its significance in food processing.

Question 8: Explain the fermentation process involving yeast and its role in the baking industry. Discuss how yeast reproduces and produces carbon dioxide, influencing the volume of dough in bread making.

Answer: Yeast plays a key role in the baking industry through the fermentation process. Yeast reproduces rapidly and produces carbon dioxide during respiration. The bubbles of this gas fill the dough, increasing its volume. This is the basis of using yeast in making breads, pastries, and cakes, providing them with a light and fluffy texture.

Question 9: Investigate the commercial uses of microorganisms, emphasizing their role in the large-scale production of alcohol, wine, and acetic acid. Provide details on how yeast is employed for these purposes.

Answer: Microorganisms, particularly yeast, are utilized in the large-scale production of alcohol, wine, and acetic acid (vinegar). Yeast is grown on natural sugars present in grains like barley, wheat, rice, and crushed fruit juices. The fermentation process carried out by yeast results in the production of alcohol and wine, showcasing the commercial applications of microorganisms.

Question 10: Examine the environmental role of microorganisms in cleaning up organic wastes. Provide examples of organic wastes mentioned in the text and explain how bacteria break them down into harmless and usable substances.

Answer: Bacteria play a significant role in cleaning up the environment by breaking down organic wastes. Examples of organic wastes include vegetable peels, remains of animals, and faeces. Bacteria decompose these wastes, converting them into harmless and usable substances. The process aids in waste management and recycling within the ecosystem.

Question 11: Explain how antibiotics work to combat disease-causing microorganisms, and provide examples of commonly known antibiotics.

Answer: Antibiotics function by either killing or inhibiting the growth of disease-causing microorganisms. Streptomycin, tetracycline, and erythromycin are examples of antibiotics made from bacteria and fungi. These drugs are produced by cultivating specific microorganisms and are employed in treating various diseases.

Question 12: Discuss the use of antibiotics in livestock and poultry. How do they contribute to animal health and prevent plant diseases?

Answer: Antibiotics are incorporated into the feed of livestock and poultry to prevent microbial infections in animals. Additionally, they are utilized to control several plant diseases. The inclusion of antibiotics in animal feed helps maintain their health and ensures disease prevention, while also acting as a protective measure against plant diseases.

Question 13: Highlight the importance of caution when using antibiotics. What precautions should individuals take while using antibiotics?

Answer: It is crucial to use antibiotics only under the guidance of a qualified doctor. Completing the prescribed course is essential, as taking antibiotics incorrectly or unnecessarily can reduce their effectiveness in the future. Overuse may also lead to the destruction of beneficial bacteria in the body. Cold and flu, caused by viruses, are conditions against which antibiotics are ineffective.

Question 14: Explain the mechanism of a vaccine and how it provides long-term protection against disease-causing microbes.

Answer: A vaccine works by introducing dead or weakened microbes into the body, prompting the immune system to produce antibodies. These antibodies remain in the body, providing long-term protection against disease-causing microbes. The body’s ability to remember how to fight the microbe ensures continued protection.

Question 15: Describe the discovery of the smallpox vaccine by Edward Jenner in 1798. What impact did this discovery have on global health

Answer: Edward Jenner discovered the smallpox vaccine in 1798, a groundbreaking achievement in the history of medicine. This discovery played a pivotal role in preventing smallpox and contributed to a worldwide campaign that eventually led to the eradication of smallpox from most parts of the world.

Question 16: Provide examples of diseases for which vaccines are administered in childhood. Discuss the importance of childhood vaccinations.

Answer: Childhood vaccinations protect against various diseases, including cholera, tuberculosis, smallpox, and hepatitis. It is essential to protect children against these diseases, and necessary vaccines are readily available in nearby hospitals. Childhood vaccinations contribute significantly to public health by preventing the spread of infectious diseases.

Question 17: Explain the significance of the Pulse Polio Programme and the role of polio drops in the vaccination process.

Answer: The Pulse Polio Programme aims to protect children against polio through widespread vaccination efforts. Polio drops given to children as part of this program act as a vaccine, preventing the occurrence and spread of polio.

Question 18: Discuss the outcomes of the global campaign against smallpox. How has smallpox been addressed on a global scale?

Answer: The worldwide campaign against smallpox resulted in the eradication of the disease from most parts of the world. This accomplishment signifies the success of global efforts to eliminate a severe infectious disease through vaccination campaigns and public health initiatives.

Question 19: Elaborate on the large-scale production of vaccines from microorganisms. How do vaccines protect humans and animals from diseases?

Answer: Vaccines are produced on a large scale from microorganisms to safeguard humans and animals from various diseases. The introduction of dead or weakened microbes triggers the production of antibodies, providing immunity and protection against disease-causing microorganisms.

Question 20: Explain the role of biological nitrogen fixers, specifically bacteria, in increasing soil fertility.

Answer: Certain bacteria, known as biological nitrogen fixers, have the capability to fix nitrogen from the atmosphere. This process enriches the soil with nitrogen, leading to increased soil fertility. The presence of these microbes aids in enhancing the nutritional content of the soil, benefiting plant growth and agricultural productivity.

Question 21: Provide insights into nitrogen fixation by Rhizobium in leguminous plants, emphasizing the symbiotic relationship with beans and peas. Discuss alternative ways nitrogen gets fixed and how the nitrogen cycle remains constant.

Answer: Rhizobium, found in the root nodules of leguminous plants like beans and peas, plays a crucial role in nitrogen fixation. It forms a symbiotic relationship with these plants, facilitating the conversion of atmospheric nitrogen into usable compounds. While nitrogen can also be fixed through the action of lightning, the overall amount of nitrogen in the atmosphere remains constant. The nitrogen cycle involves certain bacteria and blue-green algae fixing nitrogen from the atmosphere, making it usable for plants through their root system. The cycle ensures a constant percentage of nitrogen in the atmosphere by balancing conversion and release processes

Question 22: Explain the difference between the contents of pot A and pot B. Why did the polythene bags, empty glasses, bottles, and broken toy parts in pot B not undergo any change?

Answer: The contents of pot A, which contained plant waste, decomposed and converted into manure due to the action of microbes. In contrast, the polythene bags, empty glasses, bottles, and broken toy parts in pot B did not undergo any change. Microbes could not ‘act’ on these non-biodegradable materials, and they remained unchanged. Unlike the organic plant waste, these materials are resistant to microbial decomposition.

Question 23: Discuss the role of microorganisms in cleaning up the environment. Provide examples of how microorganisms can be used to degrade harmful substances.

Answer: Microorganisms play a vital role in cleaning up the environment by decomposing dead organic waste of plants and animals. They convert this waste into simple substances that can be used by other plants and animals. For example, microbes can be used to degrade harmful and smelly substances, contributing to environmental cleanliness. In waste management, microorganisms are utilized to break down organic matter in composting and sewage treatment processes, reducing environmental pollution.

Question 24: Define pathogens and explain how they can cause diseases in humans. Provide examples of communicable diseases mentioned in the text.

Answer: Pathogens are disease-causing microorganisms. They enter the human body through the air, water, or food, and can also be transmitted by direct contact with an infected person or carried by an animal. Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, food, or physical contact. Examples mentioned in the text include cholera, common cold, chickenpox, and tuberculosis.

Question 25: Describe the process of disease transmission through sneezing. What preventive measures are recommended to avoid the spread of infections?

Answer: When a person suffering from a common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. These viruses may enter the body of a healthy person while breathing, causing infection. To prevent the spread of infections, it is recommended to keep a handkerchief on the nose and mouth while sneezing and maintain a distance from infected persons.

Question 26: Explain the role of Housefly as a carrier of disease-causing microbes. How can the spread of diseases through Houseflies be avoided?

Answer: Houseflies act as carriers of disease-causing microbes by sitting on garbage and animal excreta where pathogens stick to their bodies. When these flies sit on uncovered food, they may transfer the pathogens, leading to sickness in those who consume the contaminated food. To avoid the spread of diseases through Houseflies, it is advisable to keep food covered and avoid consuming uncovered items of food.

Question 27: Discuss the role of female Anopheles mosquito as a carrier of the malaria parasite. What measures can be taken to control the spread of malaria?

Answer: The female Anopheles mosquito acts as a carrier of the malaria parasite (Plasmodium). When the mosquito bites, it can transmit the parasite to humans, causing malaria. To control the spread of malaria, measures include preventing the breeding of mosquitoes by avoiding the collection of water in coolers, tires, flower pots, etc. Keeping the surroundings clean and dry helps in preventing mosquitoes from breeding.

Question 28: Explain how mosquitoes, including the female Aedes mosquito, contribute to the spread of diseases. What measures can be implemented to avoid the spread of diseases like dengue?

Answer: Mosquitoes, including the female Aedes mosquito, contribute to the spread of diseases by acting as carriers of pathogens. For example, the female Aedes mosquito acts as a carrier of the dengue virus. To avoid the spread of diseases like dengue, it is crucial to prevent mosquito breeding by not letting water collect in various places such as coolers, tires, and flower pots. Keeping the surroundings clean and dry helps in preventing mosquitoes from breeding.

Question 29: Explain the role of microorganisms in causing diseases in animals, providing examples like anthrax and foot and mouth disease.

Answer: Microorganisms play a significant role in causing diseases not only in humans and plants but also in animals. Anthrax is an example of a dangerous disease affecting both humans and cattle, caused by a bacterium. Another instance is foot and mouth disease in cattle, which is caused by a virus. These diseases can have severe consequences on the health and well-being of animals, leading to economic losses and affecting various ecosystems.

Question 30: Discuss the impact of microorganisms on plant health, mentioning specific crops affected and the role of chemicals in controlling plant diseases.

Answer: Several microorganisms cause diseases in plants, negatively impacting crop yields. Crops like wheat, rice, potato, sugarcane, orange, and apple are susceptible to these diseases, leading to a reduction in productivity. To counteract this, chemicals are employed to control the growth of these microbes. This involves the use of certain chemicals that act as preservatives, effectively killing the microbes and preventing the spread of diseases in plants.

Question 31: Describe the scenario of food poisoning and its potential causes related to the consumption of spoilt food due to microorganisms. Explain the importance of preserving food to prevent food poisoning.

Answer: Food poisoning occurs when individuals consume food that has been contaminated or spoilt by harmful microorganisms. Microorganisms growing on food can produce toxic substances, making the food poisonous and causing serious illness or even death. To prevent such instances, it is crucial to preserve food effectively. Preserving food helps inhibit the growth of harmful microbes, ensuring the safety of the food we consume and preventing the occurrence of food poisoning.

Question 32: Explore the methods used for preserving cooked food at home, elaborating on the impact of microorganisms on food spoilage. Discuss whether the spoiling of food is a chemical reaction.

Answer: Preserving cooked food at home is essential to prevent food spoilage caused by microorganisms. Microorganisms can spoil food, leading to a bad smell, taste, and changed color. The spoiling of food is a biological process driven by various chemical reactions initiated by microorganisms. The common methods of preserving food involve using chemicals such as salts and edible oils, creating an environment that impedes microbial growth and ensures the longevity of cooked food.

Question 33: Explain the significance of chemical methods in preserving food, detailing the application of salts and edible oils as preservatives. Provide examples of common preservatives like sodium benzoate and sodium metabisulphite.

Answer: Chemical methods, involving the use of preservatives, are crucial for preventing the growth of microorganisms in food. Salts and edible oils are commonly used chemicals that act as preservatives. In pickles, for instance, salt or acid preservatives are added to prevent microbial attacks. Sodium benzoate and sodium metabisulphite are examples of common preservatives used in jams and squashes to check spoilage, ensuring the safety and longevity of various food products.

Question 34: Elaborate on the traditional use of common salt in preserving meat and fish, emphasizing its effectiveness in inhibiting the growth of bacteria. Discuss other food items preserved using common salt.

Answer: Common salt has been employed traditionally to preserve meat and fish by covering them with dry salt, preventing the growth of bacteria. Salting creates an environment that inhibits microbial activity, ensuring the longevity of these food items. Additionally, common salt is used to preserve amla, raw mangoes, tamarind, and various other food items. The practice of salting has been effective in preserving different types of food throughout history.

Question 35: Discuss the role of sugar in preserving jams, jellies, and squashes, highlighting how sugar reduces the moisture content and inhibits the growth of bacteria. Provide insights into the preservation mechanism.

Answer: Sugar plays a crucial role in preserving jams, jellies, and squashes by reducing the moisture content in these products. The reduction in moisture inhibits the growth of bacteria, preventing spoilage. The preservation mechanism involves creating an environment with low water activity, making it inhospitable for microbial growth. This method has been effective in extending the shelf life of various sugary preserves.

Question 36: Explain how the combination of oil and vinegar prevents spoilage of pickles. Discuss the broader application of this preservation method for vegetables, fruits, fish, and meat.

Answer: The combination of oil and vinegar creates an environment that prevents spoilage of pickles by making it inhospitable for bacteria. Bacteria cannot thrive in such an environment, ensuring the preservation of pickles. This preservation method is not limited to pickles; it is also applied to preserve vegetables, fruits, fish, and meat. The use of oil and vinegar has proven effective in extending the storage life of various food items.

Question 37: Describe the impact of heat and cold treatments in preserving food, using the example of boiling milk. Explain how boiling kills microorganisms and how low temperatures in refrigeration inhibit microbial growth.

Answer: Heat and cold treatments are integral in preserving food. Boiling milk, for instance, kills many microorganisms by subjecting them to high temperatures. Similarly, refrigeration involves storing food at low temperatures, inhibiting the growth of microbes. These treatments are crucial in maintaining the safety and quality of food products, providing an effective means of preserving perishable items.

Question 38: Explore the concept of pasteurization, detailing the process discovered by Louis Pasteur. Discuss how pasteurization ensures the safety of milk by preventing the growth of harmful microbes.

Answer: Pasteurization, discovered by Louis Pasteur, is a process that involves heating milk to about 70°C for 15 to 30 seconds, followed by sudden chilling and storage. This process effectively kills harmful microbes present in milk, ensuring its safety for consumption. Pasteurization has been a revolutionary method in preserving milk without compromising its nutritional value, contributing significantly to public health.

Question 39: Discuss the contemporary practice of storing dry fruits and vegetables in sealed airtight packets. Explain how this method prevents the attack of microbes and ensures the preservation of these food items.

Answer: In modern times, dry fruits and vegetables are often sold in sealed airtight packets as a preservation method. This packaging prevents the attack of microbes, maintaining the freshness and quality of the products. Sealed packets create a barrier, protecting the contents from external contaminants and microbial spoilage. This contemporary practice has become integral to the food preservation industry.