Microorganisms: Friend And Foe Worksheet

Objective Type Questions

1. Complete the table below by choosing the appropriate terms given in brackets.
   (fungi, air, citrus canker, foot and mouth, virus, insect)
   
2. Name the following.
   (a) The scientist who discovered the vaccine for smallpox.
   (b) Microorganism used in making curd from milk.
   (c) Microorganism used in large scale production of alcohol.
   (d) Instrument required to see the microorganisms.
   (e) The insect which is the carrier of malarial parasite.
   
   
3. Match the terms in column A with appropriate terms in column B.
   
4. State whether the following statements are true or false. Correct and rewrite the false statements.
   (a) Meat and fish are covered with sugar to check the growth of bacteria.
   (b) Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
   (c) Vegetables, fruits, fish, and meat can be preserved by the method of pasteurization.
   (d) High temperature inhibits the growth of microbes.
   (e) Pasteurised milk can be consumed without boiling as it is free from harmful microbes.
   
   Multiple Choice Questions
   
   
5. Microorganisms are classified into
   (a) Four groups – Bacteria, Algae, Fungi and Protozoa
   (b) Four groups - Bacteria, Algae, Fungi and Virus
   (c) Three groups - Bacteria, Algae and Fungi
   (d) Three groups - Bacteria, Algae and Virus
   
   
6. Padmashri saw some greenish cottony mass on the bread which she had left open in her kitchen for 2-3 days. Which group of microorganism is responsible for this growth?
   (a) Algae
   (b) Protozoa
   (c) Fungi
   (d) Bacteria
   
   
7. Which of the following statements about viruses is true?
   (a) They are much bigger in size than bacteria.
   (b) They show most of the characteristics of living things.
   (c) They can reproduce and multiply only inside a host cell.
   (d) They do not cause diseases in plants, animals, and humans.
   
   
8. Few statements about antibiotics are given below. Identify the true statements.
   
   (a) I and II
   (b) II and III
   (c) I and IV
   (d) II and IV
   
   
9. Cyanobacteria are commonly called nitrogen fixers. They increase the fertility of the soil. How do these nitrogen fixers increase the soil fertility?
   (a) They produce nitrogen gas that is released into the atmosphere.
   (b) They convert nitrogen gas present in the atmosphere into compost.
   (c) They fix atmospheric nitrogen to make nitrogen compounds in the soil.
   (d) They decompose remains of plants and animals to produce nitrogen compounds.
   
   
10. Which of the following correctly defines a pathogen?
    (a) Microbes which form curd
    (b) Microbes which decrease soil fertility
    (c) Microbes which cause diseases
    (d) Microbes which breakdown the remains of dead organisms
    
    
11. Which statement associated with mosquito helps us understand that malaria is a communicable disease?
    (a) The causative agent of malaria is a protozoan.
    (b) The mosquito carries the parasite Plasmodium that causes malaria.
    (c) The mosquito lays its eggs in water collected in tyres, coolers, and open pits.
    (d) The parasite is transferred inside the body of a healthy person through mosquito bite.
    
    
12. What is true about the communicable disease ‘dengue’?
    (a) It spreads due to female Aedes mosquitoes that act as carriers of dengue virus.
    (b) It spreads due to male Aedes mosquitoes that act as carriers of dengue virus.
    (c) It spreads due to male Anopheles mosquitoes that act as carriers of dengue virus.
    (d) It spreads due to female Anopheles mosquitoes that act as carriers of dengue virus.
    
    
13. Which of the following shows the correct match of the disease with its causative agent?
    

    	Disease	Affects	Caused by
    (a)	Anthrax	Plants	Bacterium
    (b)	Cholera	Animals	Fungus
    (c)	Citrus canker	Animals	Bacterium
    (d)	Rust of wheat	Plants	Fungus

      
14. Riddhi observed that the fishes were coated with salt and kept in a tray in the fish market. What is the likely use of coating fish with salt?
    (a) It increases the moisture content of the fish allowing it to survive longer.
    (b) It stops the growth of bacteria by reducing the moisture content.
    (c) It increases the salt content of the fish that enhances its taste.
    (d) It reduces the weight of the fish making the transport easier.
    
    Subjective Questions
    
    
15. Yash’s mother got him vaccinated with DTaP vaccine in his childhood.
    (a) Why is this vaccine given?
    (b) Explain how vaccines help to develop immunity against diseases.
    
    
16. Manish took two pots X and Y. He placed fruit peels, tea leaves and vegetable waste in pot X and polythene bag, glass bottle and plastic toy in pot Y. He placed both the pots in an open area for 3- 4 weeks and observed the contents in both the pots.
    (a) What will Manish observe in pots X and Y?
    (b) What could be the reason for the above changes?
    (c) How can microorganisms be used to clean the environment?
    
    
17. Why it is advisable to always keep the food covered?
    
    
18. The given diagram depicts a nitrogen cycle in nature. Fill in the missing boxes by choosing the appropriate steps stated below.
    
    
    
    Case-Based Questions
    
    
19. Shreeya mixed some maida flour with water and sugar and added a small amount of yeast powder in the mixture. She left the dough undisturbed for 4-5 hours.
    a) What will happen to the dough after 4-5 hours?
    (a) The dough will rise and increase in volume.
    (b) The dough will shrink and decrease in volume.
    (c) The dough will have no effect.
    (d) The dough will turn greenish and emit a foul smell.
    
    b) Which gas is produced by the yeast cells?
    (a) Nitrogen
    (b) Carbon dioxide
    (c) Oxygen
    (d) Carbon monoxide
    
    c) Why is yeast used in making bread, cakes, and pastries?
    
    d) To which group of microorganisms does yeast belong?
    (a) Fungi
    (b) Protozoa
    (c) Bacteria
    (d) Virus
    
    
20. In 1929, Alexander Fleming was working on a culture of disease-causing bacteria. Suddenly he found the spores of a little green mould in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. This led to the discovery of an antibiotic.
    a) Define antibiotics.
    b) Which of the following correctly states the source organism and the antibiotic discovered by Fleming?
    

    	Source organism	Antibiotic
    (a)	Fungus - Penicillium	Penicillin
    (b)	Bacteria - Penicillium	Penicillin
    (c)	Fungus - Streptomyces	Streptomycin
    (d)	Bacteria - Streptomyces	Streptomycin

    
    c) Salina has cold and viral fever for the past 5 days. Her mother gave her antibiotics, but she is not recovering. What can be a likely reason for the same?
    (a) Antibiotics are not effective against viral infections.
    (b) Antibiotics are used against bacterial infections.
    (c) Antibiotics take time to cure the infection.
    (d) Antibiotics are used to prevent infections rather than cure them.
    
    Assertion-Reasoning Questions
    
    Below questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
    
21. Assertion (A): Preservatives are added to food to prevent the attack of microbes.
    Reason (R): Sodium benzoate and sodium metabisulphite are common preservatives.
    
    
22. Assertion (A): Rhizobium bacterium lives in the root nodules of leguminous plants.
    Reason (R): Rhizobium and legumes share a parasitic relationship with each other.
    
    
23. Assertion (A): We should not let water collect anywhere in the neighbourhood.
    Reason (R): Mosquitoes breed in stagnant water and spread diseases.

Objective Type Questions

1. Complete the table below by choosing the appropriate terms given in brackets.
   (fungi, air, citrus canker, foot and mouth, virus, insect)
   
   
   Solution:
   (a) virus
   (b) insect
   (c) foot and mouth
   (d) citrus canker
   (e) air
   (f) fungi
   
   
2. Name the following.
   (a) The scientist who discovered the vaccine for smallpox.
   (b) Microorganism used in making curd from milk.
   (c) Microorganism used in large scale production of alcohol.
   (d) Instrument required to see the microorganisms.
   (e) The insect which is the carrier of malarial parasite.
   
   Solution:
   (a) Edward Jenner
   (b) Lactobacillus
   (c) Yeast
   (d) Microscope
   (e) Female Anopheles mosquito
3. Match the terms in column A with appropriate terms in column B.
   
   
   Solution:
   (a) Chlamydomonas – ii) Algae
   (b) Paramecium – v) Protozoa
   (c) Aspergillus – iv) Fungi
   (d) HIV – i) Virus
   (e) Lactobacillus – iii) Bacteria
   
   
4. State whether the following statements are true or false. Correct and rewrite the false statements.
   (a) Meat and fish are covered with sugar to check the growth of bacteria.
   (b) Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
   (c) Vegetables, fruits, fish, and meat can be preserved by the method of pasteurization.
   (d) High temperature inhibits the growth of microbes.
   (e) Pasteurised milk can be consumed without boiling as it is free from harmful microbes.
   
   Solution:
   (a) False. Meat and fish are covered with dry salt to check the growth of bacteria.
   (b) True
   (c) False. Vegetables, fruits, fish, and meat can be preserved using oil and vinegar.
   (d) False. Low temperature inhibits the growth of microbes.
   (e) True
   
   Multiple Choice Questions
   
   
5. Microorganisms are classified into
   (a) Four groups – Bacteria, Algae, Fungi and Protozoa
   (b) Four groups - Bacteria, Algae, Fungi and Virus
   (c) Three groups - Bacteria, Algae and Fungi
   (d) Three groups - Bacteria, Algae and Virus
   
   Correct Option: (a) Four groups – Bacteria, Algae, Fungi and Protozoa
   Solution: Microorganisms are classified into four major groups - Bacteria, Fungi, Protozoa and Algae. Viruses are also microscopic but are different from other microorganisms.
   
   
6. Padmashri saw some greenish cottony mass on the bread which she had left open in her kitchen for 2-3 days. Which group of microorganism is responsible for this growth?
   (a) Algae
   (b) Protozoa
   (c) Fungi
   (d) Bacteria
   
   Correct Option: (c) Fungi
   Solution: The greenish cottony mass on bread is due to the growth of fungi.
   
   
7. Which of the following statements about viruses is true?
   (a) They are much bigger in size than bacteria.
   (b) They show most of the characteristics of living things.
   (c) They can reproduce and multiply only inside a host cell.
   (d) They do not cause diseases in plants, animals, and humans.
   
   Correct Option: (c) They can reproduce and multiply only inside a host cell.
   Solution: Viruses can reproduce and multiply only inside the cells of other living organisms such as plants, animals, or bacteria. They are much smaller in size than bacteria. They do not show most of the characteristics of living things. They cause a variety of diseases in plants, animals, and humans.
   
   
8. Few statements about antibiotics are given below. Identify the true statements.
   
   (a) I and II
   (b) II and III
   (c) I and IV
   (d) II and IV
   
   Correct Option: (c) I and IV
   Solution: A person must complete the ‘full course’ of antibiotics prescribed by the doctor. Antibiotics should not be taken unnecessarily as they may kill the useful bacteria in the body and harm us.
   
   
9. Cyanobacteria are commonly called nitrogen fixers. They increase the fertility of the soil. How do these nitrogen fixers increase the soil fertility?
   (a) They produce nitrogen gas that is released into the atmosphere.
   (b) They convert nitrogen gas present in the atmosphere into compost.
   (c) They fix atmospheric nitrogen to make nitrogen compounds in the soil.
   (d) They decompose remains of plants and animals to produce nitrogen compounds.
   
   Correct Option: (c) They fix atmospheric nitrogen to make nitrogen compounds in the soil
   Solution: Cyanobacteria fix nitrogen gas from the atmosphere to enrich the soil with nitrogen compounds and increase its fertility.
   
   
10. Which of the following correctly defines a pathogen?
    (a) Microbes which form curd
    (b) Microbes which decrease soil fertility
    (c) Microbes which cause diseases
    (d) Microbes which breakdown the remains of dead organisms
    
    Correct Option: (c) Microbes which cause diseases
    Solution: Microorganisms which cause diseases are called pathogens. These disease-causing pathogens can be bacteria, fungi, virus, or protozoa.
    
    
11. Which statement associated with mosquito helps us understand that malaria is a communicable disease?
    (a) The causative agent of malaria is a protozoan.
    (b) The mosquito carries the parasite Plasmodium that causes malaria.
    (c) The mosquito lays its eggs in water collected in tyres, coolers, and open pits.
    (d) The parasite is transferred inside the body of a healthy person through mosquito bite.
    
    Correct Option: (d) The parasite is transferred inside the body of a healthy person through mosquito bite
    Solution: When a mosquito bites a person infected with malaria, the malarial parasite enters the mosquito's stomach. When this infected mosquito bites a healthy person, the person also gets infected by malaria. In this way, the disease spreads from an infected person to a healthy person.
    
    
12. What is true about the communicable disease ‘dengue’?
    (a) It spreads due to female Aedes mosquitoes that act as carriers of dengue virus.
    (b) It spreads due to male Aedes mosquitoes that act as carriers of dengue virus.
    (c) It spreads due to male Anopheles mosquitoes that act as carriers of dengue virus.
    (d) It spreads due to female Anopheles mosquitoes that act as carriers of dengue virus.
    
    Correct Option: (a) It spreads due to female Aedes mosquitoes that act as carriers of dengue virus.
    Solution: Female Aedes mosquito acts as a carrier of dengue virus and spreads the dengue from an infected person to a healthy person.
    
    
13. Which of the following shows the correct match of the disease with its causative agent?
    

    	Disease	Affects	Caused by
    (a)	Anthrax	Plants	Bacterium
    (b)	Cholera	Animals	Fungus
    (c)	Citrus canker	Animals	Bacterium
    (d)	Rust of wheat	Plants	Fungus

      
    Correct Option: (d)
    Solution:
    

    Disease	Affects	Caused by
    Anthrax	Animals and humans	Bacterium
    Cholera	Humans	Bacterium
    Citrus canker	Plants	Bacterium
    Rust of wheat	Plants	Fungus

     
14. Riddhi observed that the fishes were coated with salt and kept in a tray in the fish market. What is the likely use of coating fish with salt?
    (a) It increases the moisture content of the fish allowing it to survive longer.
    (b) It stops the growth of bacteria by reducing the moisture content.
    (c) It increases the salt content of the fish that enhances its taste.
    (d) It reduces the weight of the fish making the transport easier.
    
    Correct Option: (b) It stops the growth of bacteria by reducing the moisture content
    Solution: Meat and fish are covered with dry salt to check the growth of bacteria. Microbes require water for growth. Common salt reduces the water content of the food, thus preventing microbial growth.
    
    Subjective Questions
    
    
15. Yash’s mother got him vaccinated with DTaP vaccine in his childhood.
    (a) Why is this vaccine given?
    (b) Explain how vaccines help to develop immunity against diseases.
    
    Solution:
    (a) DTaP vaccine is given to children to prevent the occurrence of diseases - diphtheria, tetanus, and pertussis.
    (b) A vaccine contains dead or weakened but alive microorganisms of a disease. When a vaccine containing dead or alive microorganisms is introduced into the body of a healthy person orally or by injection, the body of that person responds by producing some substances called antibodies in the blood. These antibodies kill any alive disease-causing microorganisms of the disease. Some of these antibodies remain in the blood for a very long time and fight against the same microorganism and kill them if they happen to enter the body later. So, due to the presence of antibodies in the blood, a person remains protected from a particular disease. Thus, a vaccine helps develop immunity from that disease.
    
    
16. Manish took two pots X and Y. He placed fruit peels, tea leaves and vegetable waste in pot X and polythene bag, glass bottle and plastic toy in pot Y. He placed both the pots in an open area for 3- 4 weeks and observed the contents in both the pots.
    (a) What will Manish observe in pots X and Y?
    (b) What could be the reason for the above changes?
    (c) How can microorganisms be used to clean the environment?
    
    Solution:
    (a) Plant wastes containing fruit peels, tea leaves and vegetable waste in pot X has been decomposed and converted into manure. Polythene bag, glass bottle and plastic toy in pot Y do not undergo any change.
    (b) Microorganisms such as bacteria and fungi decompose the organic matter present in dead plants, dead animals, and animal wastes, and convert them into simple substances which get mixed with the soil. These substances contain plant nutrients and act as manure which are used again by new plants for their growth. The microbes do not act on polythene bags, glass bottles and plastic toys and thus, do not form manure.
    (c) Microorganisms such as bacteria and fungi decompose the organic matter present in dead plants, dead animals, and animal wastes, and convert them into manure. As they decompose the harmful and smelly dead remains of plants and animals, they help to clean the environment. They also help in recycling the nutrients in nature which can then be used as food by green plants.
    
    
17. Why it is advisable to always keep the food covered?
    
    Solution:
    Houseflies often breed on filth and refuse. When a housefly sits on a garbage heap, human excreta or other filth and refuse, millions of disease-causing microorganisms present in these wastes stick to the hairy legs and other body parts of the housefly. When this housefly sits on uncovered food, microorganisms sticking to its body parts get transferred to food. In this way, the food gets contaminated with disease-causing microorganisms. When this contaminated food is eaten by a person, the disease-causing microorganisms enter the body of that person and cause various diseases. The person gets sick. Hence, it is advisable to always keep the food covered to prevent the spread of diseases.
    
    
18. The given diagram depicts a nitrogen cycle in nature. Fill in the missing boxes by choosing the appropriate steps stated below.
    
    
    
    Solution:
    A - Nitrogen fixing bacteria fix atmospheric nitrogen
    B - Bacteria fix nitrogen into nitrogenous compounds
    C - Lightning
    D - Bacteria turn compounds of nitrogen into gaseous nitrogen
    
    Case-Based Questions
    
    
19. Shreeya mixed some maida flour with water and sugar and added a small amount of yeast powder in the mixture. She left the dough undisturbed for 4-5 hours.
    a) What will happen to the dough after 4-5 hours?
    (a) The dough will rise and increase in volume.
    (b) The dough will shrink and decrease in volume.
    (c) The dough will have no effect.
    (d) The dough will turn greenish and emit a foul smell.
    
    b) Which gas is produced by the yeast cells?
    (a) Nitrogen
    (b) Carbon dioxide
    (c) Oxygen
    (d) Carbon monoxide
    
    c) Why is yeast used in making bread, cakes, and pastries?
    
    d) To which group of microorganisms does yeast belong?
    (a) Fungi
    (b) Protozoa
    (c) Bacteria
    (d) Virus
    
    Solution:
    a) Correct option: (a) The dough will rise and increase in volume
    Solution: Yeast reproduces rapidly and gives out carbon dioxide gas during respiration. The bubbles of the gas fill the dough and increase its volume.
    
    b) Correct option: (b) Carbon dioxide
    Solution: Yeast reproduces rapidly and gives out carbon dioxide gas during respiration.
    
    c) When yeast is mixed in dough for making bread, it reproduces rapidly and gives out carbon dioxide gas during respiration. The bubbles of the gas fill the dough and increase its volume. This makes the bread rise. The carbon dioxide gas released makes the bread light, soft and spongy. Hence, yeast is used is making bread, cakes, and pastries.
    
    d) Correct option: (a) Fungi
    Solution: Yeast belongs to group Fungi.
    
    
20. In 1929, Alexander Fleming was working on a culture of disease-causing bacteria. Suddenly he found the spores of a little green mould in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. This led to the discovery of an antibiotic.
    a) Define antibiotics.
    b) Which of the following correctly states the source organism and the antibiotic discovered by Fleming?
    

    	Source organism	Antibiotic
    (a)	Fungus - Penicillium	Penicillin
    (b)	Bacteria - Penicillium	Penicillin
    (c)	Fungus - Streptomyces	Streptomycin
    (d)	Bacteria - Streptomyces	Streptomycin

    
    c) Salina has cold and viral fever for the past 5 days. Her mother gave her antibiotics, but she is not recovering. What can be a likely reason for the same?
    (a) Antibiotics are not effective against viral infections.
    (b) Antibiotics are used against bacterial infections.
    (c) Antibiotics take time to cure the infection.
    (d) Antibiotics are used to prevent infections rather than cure them.
    
    Solution:
    

    a) A medicine which stops the growth of, or kills the disease-causing microorganisms is called an antibiotic.

    b) Correct Option: (a)
    

    	Source organism	Antibiotic
    (a)	Fungus - Penicillium	Penicillin

    Solution: Penicillin is an antibiotic made from the fungus Penicillium. It controls bacterial and fungal infections.

    c) Correct Option: (a) Antibiotics are not effective against viral infections.

    Solution: Antibiotics are not effective against the diseases caused by viruses such as common cold and viral fever.

    
    Assertion-Reasoning Questions
    
    Below questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
    
21. Assertion (A): Preservatives are added to food to prevent the attack of microbes.
    Reason (R): Sodium benzoate and sodium metabisulphite are common preservatives.
    
    Correct Option: (a) Both A and R are true but R is not the correct explanation of A.
    Solution: Food often gets spoilt due to the growth of microorganisms. So, it is very important that we preserve food to prevent it from being spoilt. Preservatives are added to food to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives.
    
    
22. Assertion (A): Rhizobium bacterium lives in the root nodules of leguminous plants.
    Reason (R): Rhizobium and legumes share a parasitic relationship with each other.
    
    Correct Option: (c) A is true but R is false.
    Solution: Rhizobium bacterium lives in the root nodules of leguminous plants such as pea and beans. It shares a symbiotic relationship with these plants. The plant provides food and shelter to the bacterium. In turn, the bacterium fixes atmospheric nitrogen and makes it available to the plants.
    
    
23. Assertion (A): We should not let water collect anywhere in the neighbourhood.
    Reason (R): Mosquitoes breed in stagnant water and spread diseases.
    
    Correct Option: (a) Both A and R are true and R is the correct explanation of A
    Solution: Mosquitoes breed in stagnant water and spread diseases such as malaria. Hence, we should not let water collect anywhere in the neighbourhood. By keeping the surroundings clean and dry we can prevent the breeding of mosquitoes.