Microorganisms Friend and Foe S chand Solution by Abhinav Sir

Lakhmir Singh Science Class 8 Solutions

Chapter 2: Microorganisms - Friend and Foe

Very Short Answer Type Questions

1. Instrument needed to see microorganisms: Microscope
2. Microorganisms that reproduce only inside living cells of other organisms: Viruses
3. Major groups of microorganisms: Bacteria, Viruses, Fungi, Protozoa, Algae
4. Two human diseases caused by bacteria: Cholera, Typhoid
5. Two human diseases caused by viruses: Measles, Chickenpox
6. Two human diseases caused by protozoa: Malaria, Amoebiasis
7. Two human diseases caused by fungi: Ringworm, Athlete’s foot
8. Microorganism used in making curd from milk: Lactobacillus
9. Microorganism used for large-scale production of alcohol: Yeast
10. Two antibiotics: Streptomycin, Penicillin
11. Antibiotic extracted from fungus (mould) and the fungus: Penicillin, Penicillium
12. Four diseases preventable by vaccination: Polio, Measles, Tuberculosis, Tetanus
13. Scientist who discovered the smallpox vaccine: Edward Jenner
14. Scientist who discovered penicillin: Alexander Fleming
15. Important function performed by blue-green algae: Nitrogen fixation
16. One biological nitrogen-fixer: Rhizobium
17. Two common insects that act as carriers of disease-causing microorganisms: Housefly, Mosquito
18. Two diseases spread by housefly: Cholera, Typhoid
19. Insect that is the carrier of the malaria parasite: Female Anopheles mosquito
20. Insect that carries the dengue virus: Female Aedes mosquito
21. Which spreads dengue: mosquito or housefly?: Mosquito
22. Two diseases spread by mosquitoes: Malaria, Dengue
23. Microbe that causes malaria: Plasmodium (Protozoan)
24. One disease spread by breathing air containing microorganisms: Common cold
25. One disease spread through insect bites: Malaria
26. One disease spread through infected food or water: Cholera
27. Causative microorganisms of animal diseases:
    (a) Foot and mouth disease: Virus
    (b) Anthrax: Bacteria (Bacillus anthracis)
28. Two food materials preserved by sun-drying: Grains, Fruits (e.g., raisins, dried apricots)
29. Two food materials preserved by using common salt: Fish, Meat
30. Two food materials preserved by using sugar: Jams, Jellies
31. Two food materials preserved by deep freezing: Fish, Meat
32. Preservatives used in preservation of fruits as jams and jellies: Sugar, Sodium benzoate
33. Preservatives used in preservation of fruits and vegetables as pickles: Salt, Vinegar
34. Two food materials preserved by using oil or vinegar: Pickles, Fish
35. Two special chemicals used as food preservatives: Sodium benzoate, Sodium metabisulphite
36. Microorganisms that can fix atmospheric nitrogen in the soil: Rhizobium, Blue-green algae
37. Type of plants that can fix nitrogen gas into compounds: Leguminous plants
38. Microorganisms present in soil and root nodules of leguminous plants that fix atmospheric nitrogen: Rhizobium, Blue-green algae
39. Two leguminous plants that can fix nitrogen: Peas, Beans
40. Fill in the blanks:
    (a) Alcohol is produced with the help of Yeast.
    (b) Blue-green algae fix Nitrogen directly from air to enhance fertility of soil.
    (c) Microorganisms can be seen with the help of a Microscope.
    (d) Cholera is caused by Bacteria.
    (e) Common salt has been used to preserve Fish and Meat for ages.
    (f) The food material preserved by pasteurization is Milk.
    (g) As a result of the nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less Constant.

Long Answer Type Questions

44. How do houseflies carry disease-causing microbes?
    Houseflies pick up disease-causing microbes (bacteria, protozoa, etc.) from feces, garbage, or other waste on their legs or body. When they sit on uncovered food, these microbes are transferred, contaminating the food.
    Prevention:
    - Keep food covered to prevent flies from landing on it.
    - Avoid eating uncovered food from roadside stalls.
45. How do mosquitoes carry disease-causing microorganisms and spread diseases?
    When a female Anopheles mosquito bites a person with malaria, it ingests blood containing Plasmodium parasites. When it bites a healthy person, it transfers these parasites through its saliva, spreading malaria. Similarly, the Aedes mosquito spreads dengue助手 System: dengue by transmitting the dengue virus.
    Prevention:
    - Use fine iron wire mesh on windows and doors.
    - Spray insecticides periodically to kill mosquitoes.
    - Spray oil on stagnant water to kill mosquito larvae.
46. What is meant by fermentation? Name the scientist who discovered it.
    Fermentation is the process of converting sugars into alcohol and carbon dioxide by the action of yeast. The scientist who discovered fermentation was Louis Pasteur.
47. How do microorganisms help in increasing soil fertility?
    Microorganisms like Rhizobium and blue-green algae fix atmospheric nitrogen into compounds that plants can use, enhancing soil fertility.
48. How do microorganisms help in cleaning the environment? What are antibiotics? Precautions while taking antibiotics?
    - Cleaning the environment: Microorganisms like bacteria and fungi decompose organic waste (e.g., dead plants, animals, dung) into harmless substances, cleaning the environment.
    - Antibiotics: Medicines that kill or stop the growth of disease-causing bacteria.
    - Precautions:
    - Take antibiotics only on a doctor’s advice.
    - Complete the full course as prescribed.
    - Avoid unnecessary use, as it may kill beneficial bacteria.
49. Why are antibiotics not effective against common cold and flu?
    Antibiotics are not effective because common cold and flu are caused by viruses, and antibiotics only work against bacteria.
50. Full form of HIV and the disease caused by it:
    - Full form: Human Immunodeficiency Virus.
    - Disease: AIDS (Acquired Immune Deficiency Syndrome).
51. How is curd made from milk? Name the bacterium.
    Curd is made by adding a small amount of curd (containing Lactobacillus bacteria) to milk. Lactobacillus converts lactose sugar in milk into lactic acid, which causes milk to coagulate and form curd.
52. Microorganism used in bread-making that makes the dough rise:
    Yeast is used. It reproduces rapidly, producing carbon dioxide gas during respiration, which forms bubbles that make the dough rise, resulting in light, soft, and spongy bread.
53. What is food poisoning? How is it caused?
    - Food poisoning: A disease caused by consuming food contaminated with microorganisms or their toxic substances.
    - Cause: Microorganisms like bacteria and fungi enter food through air, dirty hands, unclean containers, houseflies, or cockroaches, leading to illness or even death.
54. What is meant by food preservation? Name five methods. How to preserve cooked food at home?
    - Food preservation: The process of treating food to prevent spoilage.
    - Five methods:
    1. Sun-drying
    2. Heating
    3. Cooling (Refrigeration)
    4. Addition of common salt
    5. Addition of sugar
    - Preserving cooked food at home:
    - Store in airtight containers and refrigerate (deep freezing).
    - Reheat thoroughly before consumption.
55. Why should we not let water collect in the neighborhood? Animal diseases caused by microorganisms.
    - Stagnant water: Provides a breeding ground for mosquitoes, which spread diseases like malaria and dengue.
    - Animal diseases:
    - (i) Virus: Foot and mouth disease
    - (ii) Bacteria: Anthrax
    - (iii) Fungus: Ringworm
56. Where do Rhizobium bacteria live? What is their function?
    - Location: Rhizobium bacteria live in the soil and in the root nodules of leguminous plants.
    - Function: They fix atmospheric nitrogen into compounds that plants can use, enhancing soil fertility.
57. Name two microorganisms in each category:
    - (a) Bacteria: Lactobacillus, Rhizobium
    - (b) Viruses: HIV, Measles virus
    - (c) Protozoa: Amoeba, Plasmodium
    - (d) Algae: Chlamydomonas, Spirogyra
    - (e) Fungi: Yeast, Penicillium
58. Beneficial effects of microorganisms in our lives:
    - Making curd (Lactobacillus).
    - Baking bread and producing alcohol (Yeast).
    - Fixing atmospheric nitrogen (Rhizobium, blue-green algae).
    - Decomposing organic waste to clean the environment.
    - Producing antibiotics (e.g., Penicillin from Penicillium).
59. Method of pasteurization for milk preservation:
    Pasteurization involves heating milk to about 70°C for 15–30 seconds and then rapidly cooling it to kill harmful microorganisms while preserving quality.
60. Plant diseases caused by:
    - (a) Fungi: Rust of wheat
    - (b) Virus: Yellow vein mosaic of bhindi (okra)
    - (c) Bacteria: Citrus canker
61. Diseases spread by:
    - (a) Female Anopheles mosquito: Malaria
    - (b) Female Aedes mosquito: Dengue
62. Fruits preserved as:
    - (a) Pickles: Mango, Lemon
    - (b) Jams: Apple, Strawberry
63. Mode of transmission of plant diseases:
    - (a) Rust of wheat: Air (spores carried by wind)
    - (b) Citrus canker: Contact (through infected plant material or water splashes)
    - (c) Yellow vein mosaic of bhindi: Insect vectors (whiteflies)
64. Animal and plant diseases caused by microorganisms:
    - Animal diseases: Foot and mouth disease (Virus), Anthrax (Bacteria)
    - Plant diseases: Rust of wheat (Fungi), Citrus canker (Bacteria)
65. Causative microorganisms and modes of transmission of human diseases:
    - (i) Tuberculosis: Bacteria (Mycobacterium tuberculosis), Air
    - (ii) Measles: Virus, Air
    - (iii) Chickenpox: Virus (Varicella-zoster), Air/Contact
    - (iv) Polio: Virus (Poliovirus), Water/Food
    - (v) Cholera: Bacteria (Vibrio cholerae), Water/Food
    - (vi) Typhoid: Bacteria (Salmonella typhi), Water/Food
    - (vii) Hepatitis B: Virus (Hepatitis B virus), Blood/Body fluids
    - (xii) Malaria: Protozoan (Plasmodium), Insect bite (Female Anopheles mosquito)
    - (x) Dengue: Virus, Insect bite (Female Aedes mosquito)
66. What are communicable diseases? Name two. Ways they occur and spread:
    - Communicable diseases: Diseases that spread from an infected person to a healthy person through air, water, or physical contact.
    - Examples: Common cold, Cholera
    - Ways they occur and spread:
    - Breathing air containing microorganisms (e.g., common cold).
    - Consuming infected food or water (e.g., cholera).
    - Insect bites (e.g., malaria, dengue).
    - Physical contact with an infected person or their belongings.
67. Five human diseases, causative microorganisms, and mode of transmission. Ways to prevent communicable diseases:
    - Diseases:
    1. Tuberculosis: Bacteria (Mycobacterium tuberculosis), Air
    2. Cholera: Bacteria (Vibrio cholerae), Water/Food
    3. Measles: Virus, Air
    4. Malaria: Protozoan (Plasmodium), Insect bite (Female Anopheles mosquito)
    5. Dengue: Virus, Insect bite (Female Aedes mosquito)
    - Prevention:
    - Cover mouth/nose while sneezing.
    - Keep food covered to avoid contamination.
    - Use disposable syringes.
    - Vaccinate at the appropriate time.
68. What is a vaccine? How does it work? Why are children vaccinated?
    - Vaccine: A preparation containing dead or weakened microorganisms that provides immunity against a specific disease.
    - How it works: It stimulates the production of antibodies, which remain in the blood and fight off the same microorganisms later, providing immunity.
    - Why children are vaccinated: To build strong immunity and protect against diseases for good health.
69. What is nitrogen fixation? Two ways it occurs in nature:
    - Nitrogen fixation: The process of converting atmospheric nitrogen gas into compounds usable by plants.
    - Two ways:
    - By nitrogen-fixing bacteria like Rhizobium in the root nodules of leguminous plants.
    - By blue-green algae in the soil.
70. Nitrogen cycle diagram and natural phenomenon responsible for nitrogen fixation:
    - Diagram: Shows atmospheric nitrogen fixed by bacteria (e.g., Rhizobium) or lightning, absorbed by plants, consumed by animals, decomposed by microorganisms, and returned to the atmosphere via denitrification.
    - Natural phenomenon: Lightning (converts nitrogen gas into nitrates in the soil).

Multiple Choice Questions (MCQs)

71. The bread dough rises because of: (c) Growth of yeast cells
72. Yeast is used in the production of: (b) Alcohol
73. The process of conversion of sugar into alcohol is called: (c)超過 System: Fermentation
74. Which is an antibiotic?: (b) Streptomycin
75. The most common carrier of communicable diseases: (b) Housefly
76. The carrier of malaria-causing protozoan: (a) Female Anopheles mosquito
77. The vaccine for smallpox was discovered by: (b) Edward Jenner
78. Alcohol can be converted into vinegar by the action of: (d) Bacteria
79. The first antibiotic called penicillin was extracted from: (c) A fungus
80. Which is not a communicable disease?: (b) Cancer
81. Microorganisms that reproduce and multiply only in cells of other organisms: (d) Viruses
82. Dengue disease spread by Aedes mosquito is caused by: (b) Virus
83. Which disease is not caused by viruses?: (c) Cholera
84. Microorganism capable of converting sugar into alcohol and carbon dioxide: (b) Fungus (Yeast)
85. Which is not a use of microorganisms?: (b) Preparation of food by photosynthesis
86. Malaria is caused by: (b) Protozoan
87. The parasite Plasmodium causes: (c) Malaria

Questions Based on High Order Thinking Skills (HOTS)

91. Disease after consuming mutton with nausea, vomiting, diarrhea, and abdominal pain:
    - (a) Food poisoning
    - (b) Microorganisms (bacteria or fungi) present in the spoiled mutton.
92. Match the microorganism with their action:
    - (i) Bacteria → (e) Causing cholera
    - (ii) Rhizobium → (a) Fixing nitrogen
    - (iii) Lactobacillus → (b) Setting of curd
    - (iv) Yeast → (c) Baking of bread
    - (v) A protozoan → (d) Causing malaria
    - (vi) A virus → (f) Causing AIDS
    - (vii) Penicillin → (g) Producing antibiotics
93. Category of microorganisms:
    - Amoeba: Protozoa
    - Lactobacillus: Bacteria
    - Chlamydomonas: Algae
    - Penicillium: Fungi
    - Yeast: Fungi
    - HIV: Virus
94. Causative microorganisms of plant diseases:
    - (a) Rust of wheat: Fungus
    - (b) Citrus canker: Bacteria
    - (c) Yellow vein mosaic of bhindi: Virus
95. Mosquito-related questions:
    - (a)
    - (i) Mosquito P: Aedes mosquito
    - (ii) Disease Q: Dengue
    - (b)
    - (i) Mosquito R: Anopheles mosquito
    - (ii) Protozoan S: Plasmodium
    - (iii) Disease T: Malaria
    - (c) Sex of mosquito P: Female
    - (d) Sex of mosquito R: Female