Microorganisms Friend and Foe Class 8 Science Chapter 2 Extra Questions and Answers are provided here. We prepared these extra questions based on the latest NCERT Class 8 Science Book. CBSE Class 8 Science Chapter 2 Microorganisms: Friend and Foe Extra Questions will help you to properly understand a particular concept of the chapter.

Class 8 Science Chapter 2 Microorganisms: Friend and Foe Extra Questions

Very short Answer Type Questions

Question 1: What causes malaria?

Answer: Malaria is caused by protozoa.

Question 2: Which mosquito act as carrier of dengue virus?

Answer: Aedes mosquito acts as carrier of dengue virus.

Question 3: Name any two diseases that can be prevented by vaccination.

Answer: Polio and smallpox

Question 4: Give two examples of algae.

Answer: Chlamydomonas and Spirogyra

Question 5: Give two examples of protozoa.

Answer: Amoeba and Paramecium

Question 6: How are cholera and typhoid caused?

Answer: Cholera and typhoid are caused by bacteria.

Question 7: Give few of examples of fungi.

Answer: Bread mould, Penicillium and Aspergillus

Question 8: Who discovered penicillin?

Answer: In 1929, Alexander Fleming discovered penicillin.

Question 9: Name any two diseases caused by bacteria.

Answer: Typhoid and tuberculosis (TB)

Question 10: What causes foot and mouth disease of cattle?

Answer: Foot and mouth disease of cattle is caused by a virus.

Question 11:Who discovered the vaccine for smallpox?

Answer: Edward Jenner discovered the vaccine for smallpox in 1798.

Question 12: Name any two diseases caused by protozoa.

Answer: Diseases like dysentery and malaria are caused by protozoans.

Question 13: Name some antibiotics.

Answer: Streptomycin, tetracycline and erythromycin

Question 14: How are meat and fish preserved?

Answer: Meat and fish are covered with dry salt to check the growth of bacteria.

Question 15: What is fermentation?

Answer: The process of conversion of sugar into alcohol is called fermentation.

Question 16: Why do we boil milk before storing?

Answer: We boil milk before storing because boiling kills many microorganisms.

 Question 17: Name one plant disease caused by bacteria and its mode of transmission.

Answer: Citrus canker is caused by bacteria and transmitted through air.

Question 18: Why are the antibiotics not effective against colds and the flu?

Answer: Antibiotics are not effective against cold and flu as these are caused by viruses.

Question 19: Name one plant disease caused by virus and its mode of transmission.

Answer: Yellow vein mosaic of bhindi (Okra) is caused by virus and transmitted through insect.

Question 20: How can we control plant diseases?

Answer: They can be controlled by the use of certain chemicals which kill the microbes.

Question 21: Name one plant disease caused by fungi and its mode of transmission.

Answer: Rust of wheat is caused by fungi and transmitted through air and seeds.

Question 22: What causes food poisoning?

Answer: Food poisoning could be due to the consumption of food spoilt by some microorganisms.

Question 26: How do we preserve pickles?

Answer: We add salt or acid preservatives to pickles to prevent the attack of microbes.

Question 27: What are preservatives?

Answer: Chemicals (Salts, edible oils etc.) used to check the growths of microorganisms are called preservatives.

Question 28: Why pasteurized milk can be consumed without boiling?

Answer: Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Short Answer Type Question

Question 1: Name some unicellular and multicellular organisms.

Answer: Unicellular organisms- bacteria, some algae and protozoa

Multicellular organisms- algae and fungi

Question 2: How can we prevent the spread of communicable diseases?

Answer: We prevent the spread of communicable diseases:

• By keeping handkerchief on the nose and mouth while sneezing.
• By keeping distance from infected persons.

Question 3: How are viruses different from other microorganisms?

Answer: Viruses are quite different from other microorganisms. They reproduce only inside the host organism; bacterium, plant or animal cell.

Question 4: How do microorganisms clean the environment?

Answer: Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.

Question 5: How are jams and squashes preserved?

Answer: Sodium benzoate and sodium metabisulphite are used in the jams and squashes to check their spoilage.

Question 6: What are the major groups of microorganisms?

Answer: Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.

Question 7: What are microorganisms?

Answer: Microorganisms or microbes are the living organisms around us which cannot be seen with naked eye.

Question 8: What diseases are prevented through vaccination?

Answer: Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

Question 9: Why do we keep food in refrigerator?

Answer: We keep food in the refrigerator because low temperature inhibits the growth of microbes and keep the food fresh.

Question 10: Why dry fruits and even vegetables are sold in sealed air tight packets?

Answer: Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Question 11: Why is it important to vaccinate small children?

Answer: It is important to vaccinate small children in order to protect them against several diseases.

Question 12: Who discovered the bacterium which causes anthrax disease?

Answer: Robert Köch (1876) discovered the bacterium (Bacillus anthracis) which causes anthrax disease.

Question 13: How are cholera and typhoid transmitted?

Answer: Cholera is transmitted through water or food. Typhoid is transmitted through water.

Question 14: Write any two common cattle diseases and its cause.

Answer: Anthrax is a dangerous cattle disease caused by a bacterium.

Foot and mouth disease of cattle is caused by a virus.

Question 15: Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.

Question 16: Why sugar is used as preservative?

Answer: Sugar is used as preservative in jams, jellies and squashes. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.

Question 17: Which microorganism is used for commercial production of alcohol, wine and acetic acid (vinegar)?

Answer: Yeast is used for commercial production of alcohol, wine and acetic acid (vinegar).

Question 18: Name some commonly known antibiotics which are made from fungi and bacteria.

Answer: Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

Question 19: What are the harmful effects of microorganisms on plants?

Answer: Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops.

Question 20: Name some diseases caused by virus.

Answer: Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses.

Question 21: How does food become poisonous?

Answer: Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Question 22: How can we prevent the spread of hepatitis B?

Answer: Ways to prevent the spread of hepatitis B

• Drink boiled drinking water.
• Vaccination

Question 23: Name the bacterium found in the roots of pea plant. How is this bacterium useful?

Answer: Rhizobium lives in the root nodules of leguminous plants such as beans and peas. It is involved in the fixation of nitrogen in leguminous plants (pulses).

Question 24: Why should we keep our food covered?

Answer: Flies sit on uncovered food and they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. So, it is advisable to always keep food covered.

Question 25: Why are viruses considered to be on the borderline between living organisms and non-living things?

Answer: Viruses are also microscopic. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

Question 26:  Write some common uses of yeast.

Answer: Common uses of yeast are:

• It is used in the baking industry for making breads, pastries and cakes.
• It is used for commercial production of alcohol and wine.

Long Answer Type Question

Question 1: How can food be preserved by adding oil and vinegar?

Answer: Use of oil and vinegar prevents spoilage of food because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

Question 2:  How milk is turned into curd?

Answer: A little curd is added to warm milk to set curd. Curd contains several microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.

Question 3: How does common cold spread?

Answer: When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing.

Question 4: Why is tuberculosis considered as infectious disease?

Answer: Tuberculosis is considered as infectious disease because bacteria that cause tuberculosis are spread from one person to another through tiny droplets released into the air via coughs and sneezes.

Question 5: What causes tuberculosis and how is it spread?

Answer: Tuberculosis is caused by bacteria that spread from person to person through microscopic droplets released into the air. This can happen when someone with tuberculosis coughs, speaks, sneezes or spits.

Question 6: What are biological nitrogen fixers?

Answer: Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Question 7: How can cholera be prevented?

Answer: To prevent cholera we must:

• Maintain personal hygiene and good sanitary habits.
• Consume properly cooked food and boiled drinking water.
• Vaccination.

Question 8: What are pathogens?

Answer: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens.

Question 9: How do pathogens enter our body?

Answer: Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal.

Question 10:  Why should we not let water collect anywhere in the neighbourhood?

Answer: All mosquitoes breed in water. Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc. By keeping the surroundings clean and dry we can prevent mosquitoes from breeding.

Question 11: What will happen if we take antibiotics when not needed?

Answer: If we take antibiotics when not needed or in wrong doses, it may make the drug less effective when we might need it in future.Also antibiotics taken unnecessarily may kill the beneficial bacteria in the body.

Question 12: What are carriers of disease-causing microbes? Give examples.

Answer: There are some insects and animals which act as carriers of disease-causing microbes. Housefly is one such carrier. Another example of a carrier is the female

Anopheles mosquito, which carries the parasite of malaria.

Question 13: What happens when yeast powder is added to sugar solution and kept for 4-5 hours?

Answer: When yeast powder is added to sugar solution and kept for 4-5 hours, fermentation takes place. Sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.

 Question 14: Why is yeast used in baking industry?

Answer: Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

Question 15: How do houseflies spread disease?

Answer: Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick.

Question 16: Write a short paragraph on the harms caused by microorganisms.

Answer: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.

Question 17: What is called pasteurization?

Answer: It is a process in which milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Question 18: What are communicable diseases? Give examples.

Answer: Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

Question 19: Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: Microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Question 20: Where do microorganisms live?

Answer: They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.

Question 21:  Why is curd an important ingredient in making rava idlis and bhaturas?

Answer: Curd is added while making idli and bhatura dough as curd contains Lactobacillus bacteria that undergoes anaerobic respiration and in this process it acts on sugar of the flour and releases carbon dioxide gas, this gas make the dough rise and when baked or fried gas escapes leaving the idli or bhatura soft and spongy.

Question 22:  How a vaccine works?

Answer: 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. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes. This is how a vaccine works.

Question 23:  Mention some important uses of fungi.

Answer: Uses of fungi are as follows:

• Some antibiotics are made from fungi.
• When plants and animals die fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.
• Yeasts are single-celled fungi. It is used in baking industry for making breads, pastries and cakes and for commercial production of alcohol and wine.

Question 24: Write 10 lines on the usefulness of microorganisms in our lives.

Answer: Microorganisms play an important role in our lives. Some of them are beneficial in many ways.

• They are used in the preparation of curd, bread and cake.
• They are used for the large-scale production of alcohol, wine and acetic acid (vinegar).                        
• They are also used in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals etc.) are broken down into harmless and usable substances by bacteria.
• Bacteria are also used in the preparation of medicines.
• In agriculture they are used to increase soil fertility by fixing nitrogen.

Question 25:  What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: Antibiotics are the medicines prepared from microorganisms to kill or stop the growth of the disease-causing microorganisms.

Precautions to be taken while taking antibiotics:

• Antibiotics should be taken only on the advice of a qualified doctor.
• Course of antibiotics should be completed as prescribed by the doctor.
• Antibiotics should be taken in the right amount and at the right time. If antibiotics are taken unnecessarily it may kill the beneficial bacteria in the body.
• Antibiotics are not effective against cold and flu as these are caused by viruses.

Question 26: Explain nitrogen cycle.

Answer: Our atmosphere has 78% nitrogen gas. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

Question 27:  What are the different methods of food preservation?

Answer: Different methods of food preservation are:

• Chemical Method – Salts and edible oils are the common chemicals generally used to check the growth of microorganisms.
• Preservation by Common Salt – Common salt has been used to preserve meat and fish for ages. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
• Preservation by Sugar – Jams, jellies and squashes are preserved by sugar.
• Preservation by Oil and Vinegar – Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
• Heat and Cold Treatments – This process kills many microorganisms. Milk is boiled before it is stored or used.
• Storage and Packing – Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.