Harmful microorganisms — Class 8 CBSE Science MCQs with Solutions
Free Class 8 CBSE Science Harmful microorganisms MCQs with step-by-step solutions (15 questions). Part of Microorganisms: Friend and Foe. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Harmful microorganisms · easy · theory
Microorganisms that cause diseases are known by what special name?
A. Pathogens ✓ Correct
B. Antibodies
C. Preservatives
D. Decomposers
Solution: Disease-causing microorganisms are called pathogens. They enter the body through air, water, food or direct contact.
Q2 — Harmful microorganisms · easy · theory
The malaria-causing parasite is carried into a person by the bite of which insect?
A. Female Anopheles mosquito ✓ Correct
B. Female Aedes mosquito
C. Housefly
D. Male Anopheles mosquito
Solution: The female Anopheles mosquito carries the malaria parasite (Plasmodium) and spreads it while biting.
Q3 — Harmful microorganisms · easy · theory
Anthrax, a dangerous disease of both humans and cattle, is caused by a member of which group of microbes?
A. Bacteria ✓ Correct
B. Virus
C. Protozoa
D. Fungi
Solution: Anthrax is caused by the bacterium Bacillus anthracis, so it belongs to the bacteria group.
Q4 — Harmful microorganisms · easy · theory
The dengue virus is spread to humans by the bite of which insect?
A. Female Aedes mosquito ✓ Correct
B. Female Anopheles mosquito
C. Housefly
D. Male Aedes mosquito
Solution: The female Aedes mosquito carries and spreads the dengue virus.
Q5 — Harmful microorganisms · easy · theory
A housefly sits on garbage and excreta and then lands on our food. What is the best way to stop it from spreading disease this way?
A. Keep our food covered ✓ Correct
B. Sleep under a mosquito net
C. Boil our drinking water
D. Complete the full antibiotic course
Solution: The housefly picks up pathogens from filth and drops them on uncovered food, so keeping food covered prevents this contamination.
Q6 — Harmful microorganisms · medium · theory
Which of the following is a communicable disease, i.e. one that spreads directly from an infected person to a healthy person?
A. Chicken pox ✓ Correct
B. Malaria
C. Foot and mouth disease
D. Yellow vein mosaic of bhindi
Solution: Chicken pox passes from an infected person to a healthy person through air and contact, so it is communicable, whereas malaria spreads through a mosquito, foot and mouth disease affects cattle, and yellow vein mosaic affects plants.
Q7 — Harmful microorganisms · medium · theory
When a person suffering from the common cold sneezes without covering the nose, how can the disease reach a healthy person standing nearby?
A. Fine droplets carrying viruses are released into the air and breathed in by the healthy person ✓ Correct
B. Bacteria from the sneeze collect in stagnant water that the healthy person later drinks
C. A mosquito picks up the virus from the sneeze and injects it by biting the healthy person
D. The virus travels through the soil and enters the healthy person through the feet
Solution: During sneezing, tiny droplets carrying thousands of cold viruses are sprayed into the air, and a healthy person nearby inhales them. This is why one should keep a handkerchief over the nose and mouth while sneezing and keep distance from infected people.
Q8 — Harmful microorganisms · medium · theory
Cholera, caused by bacteria, spreads mainly through which route?
A. Contaminated water and food ✓ Correct
B. Fine droplets in the air
C. The bite of a mosquito
D. Insects moving between plants
Solution: Cholera is a bacterial disease that spreads through contaminated water and food.
Q9 — Harmful microorganisms · medium · theory
Foot and mouth disease, which affects cattle, is caused by which type of microbe?
A. Virus ✓ Correct
B. Bacterium
C. Protozoan
D. Fungus
Solution: Foot and mouth disease of cattle is caused by a virus.
Q10 — Harmful microorganisms · medium · theory
Citrus canker is a plant disease. Which microbe causes it and how does it spread?
A. Bacteria, spreading through air ✓ Correct
B. Fungi, spreading through seeds
C. Virus, spreading through insects
D. Protozoa, spreading through water
Solution: Citrus canker is caused by bacteria and spreads through air.
Q11 — Harmful microorganisms · medium · theory
Rust of wheat, a disease that reduces crop yield, is caused by which group of microorganisms?
A. Fungi ✓ Correct
B. Bacteria
C. Virus
D. Protozoa
Solution: Rust of wheat is caused by fungi and spreads through air and seeds.
Q12 — Harmful microorganisms · medium · theory
Yellow vein mosaic of bhindi (okra) is a viral disease. How is this virus carried from one plant to another?
A. By insects ✓ Correct
B. Through the air
C. Through water
D. Through seeds
Solution: The virus causing yellow vein mosaic of okra is spread from plant to plant by insects.
Q13 — Harmful microorganisms · hard · theory
A patient is found to be suffering from both typhoid and malaria. Which option correctly identifies the microbes responsible for each?
A. Typhoid by bacteria and malaria by protozoa ✓ Correct
B. Typhoid by virus and malaria by bacteria
C. Typhoid by protozoa and malaria by virus
D. Typhoid by bacteria and malaria by virus
Solution: Typhoid is caused by bacteria while malaria is caused by a protozoan (Plasmodium).
Q14 — Harmful microorganisms · hard · theory
A person ate food left uncovered, on which a housefly had earlier sat, and later fell ill. In spreading the disease this way, the housefly is best described as a:
A. Carrier of pathogens ✓ Correct
B. Pathogen itself
C. Preservative
D. Decomposer
Solution: The housefly does not itself cause the disease but transfers pathogens from filth onto food, so it acts as a carrier.
Q15 — Harmful microorganisms · hard · theory
Why can eating food that has been spoilt by certain microbes cause serious illness or even death?
A. Some microbes growing on the food produce toxic substances ✓ Correct
B. The food loses all of its nitrogen content
C. The microbes turn the food into antibiotics
D. The spoilt food becomes a vaccine
Solution: Certain microbes growing on food produce toxic substances (toxins) that cause food poisoning, which can be serious or even fatal.