Extra 20 important long questions and answers from the chapter:2 "Microorganisms: Friend and Foe" for Class 8 Science (CBSE):-
1. What are microorganisms? Name their major groups.
Microorganisms are tiny living organisms that cannot be seen with the naked eye. They are found in air, water, soil, and even inside our bodies.
Major Groups of Microorganisms:
Bacteria
– Single-celled organisms that help in nitrogen fixation and fermentation.
Fungi
– Includes yeast and
molds
, used in food production and decomposition.
Protozoa
– Single-celled organisms that cause diseases like malaria.
Algae
– Simple, plant-like microorganisms that produce oxygen.
Viruses
– Non-living outside a host but can reproduce inside living cells.
2. How are microorganisms useful to humans?
Microorganisms are helpful in many ways:
Making curd and cheese
– Lactobacillus bacteria help in the formation of curd from milk.
Fermentation
– Yeast helps in making bread, cakes, and alcohol.
Medicine production
– Fungi like Penicillium are used to make antibiotics.
Nitrogen fixation
– Bacteria like Rhizobium convert atmospheric nitrogen into usable form.
Decomposition
– Microorganisms break down dead plants and animals, recycling nutrients.
Sewage treatment
– Certain bacteria help clean wastewater.
3. What are antibiotics? How are they useful?
Antibiotics are medicines that kill or stop the growth of harmful microorganisms.
Uses of Antibiotics:
Treat bacterial infections
– Used to cure diseases like tuberculosis and pneumonia.
Prevent infections
– Given before surgeries to avoid bacterial growth.
Used in animal husbandry
– Given to livestock to prevent infections.
Preserve food
– Antibiotics are used in some food products to prevent spoilage.
Production of vaccines
– Help in making life-saving vaccines.
Examples
– Penicillin, Streptomycin, Tetracycline.
4. Explain the role of microorganisms in agriculture.
Microorganisms are essential for agriculture in the following ways:
Nitrogen fixation
– Bacteria like Rhizobium help plants by converting atmospheric nitrogen into a usable form.
Decomposition
– Fungi and bacteria break down organic matter into nutrients for the soil.
Compost preparation
– Microorganisms help in making organic fertilizers from waste.
Biological pest control
– Some bacteria and fungi help control harmful pests naturally.
Soil fertility
– Certain microbes improve soil texture and nutrient content.
Water purification
– Microbes break down waste materials in water bodies.
5. What are vaccines? How do they work?
Vaccines are substances that stimulate the immune system to protect against diseases.
How Vaccines Work:
Contain
weakened or dead microbes
that do not cause disease.
The body recognizes the microbe and produces
antibodies
against it.
If the person is later exposed to the real disease,
antibodies fight off the infection
.
Provides
long-term immunity
.
Examples: Polio, measles, hepatitis vaccines.
Help in
eradicating deadly diseases
like smallpox.
6. How do microorganisms spoil food?
Microorganisms spoil food by growing on it and producing toxins.
Ways in which food gets spoiled:
Bacteria
– Cause souring of milk and spoilage of fruits and vegetables.
Fungi
–
Mold
grows on bread and rots fruits.
Yeast
– Ferments sugar in fruits, causing spoilage.
Bad smell and
colour
change
– Microbial activity causes unpleasant
odour
and discoloration.
Food poisoning
– Some bacteria release toxins, making food unsafe.
Examples
– Salmonella causes food poisoning, Aspergillus produces toxic substances.
7. What are food preservation methods?
Food preservation prevents spoilage by inhibiting microbial growth.
Common methods:
Refrigeration
– Slows down microbial growth.
Pasteurization
– Heating milk to kill harmful bacteria.
Salting
– Used for meat and pickles to prevent microbial growth.
Dehydration
– Drying removes moisture, preventing microbial growth.
Canning
– Storing food in airtight containers.
Using preservatives
– Chemicals like vinegar and sugar are added to food.
8. Explain the nitrogen cycle.
The nitrogen cycle is the process of nitrogen movement between the atmosphere, soil, and living organisms.
Steps in the Nitrogen Cycle:
Nitrogen fixation
– Bacteria like Rhizobium convert nitrogen gas into usable compounds.
Nitrification
– Soil bacteria convert ammonia into nitrates.
Plant absorption
– Plants absorb nitrates from the soil for growth.
Animal consumption
– Animals get nitrogen by eating plants.
Decomposition
– Dead plants and animals release nitrogen back into the soil.
Denitrification
– Bacteria convert nitrates back into nitrogen gas, releasing it into the air.
9. How do viruses differ from other microorganisms?
Viruses are different from bacteria, fungi, and protozoa in several ways:
Non-living outside a host
– Viruses are inactive outside living cells.
Require a host to reproduce
– Unlike bacteria, they cannot multiply on their own.
No cellular structure
– Viruses have DNA/RNA inside a protein coat but lack a cell membrane.
Cause deadly diseases
– Like COVID-19, polio, and AIDS.
Smaller than bacteria
– Can only be seen under an electron microscope.
Do not perform life processes
– Do not respire, grow, or move independently.
10. What are the harmful effects of microorganisms?
Microorganisms can be harmful in several ways:
Cause diseases
– Bacteria (typhoid), viruses (flu), fungi (skin infections).
Spoil food
– Fungi and bacteria cause food decay.
Destroy crops
– Pests and microbial infections damage plants.
Cause food poisoning
– Bacterial toxins make food unsafe.
Spread epidemics
– Viruses like COVID-19 spread globally.
Damage materials
– Fungi can destroy leather, wood, and fabrics.
11. Describe the role of microorganisms in wastewater treatment.
Microorganisms help in treating wastewater by breaking down harmful substances.
Bacteria and fungi
decompose organic waste in sewage.
Microbes break down pollutants
and convert them into harmless substances.
Aerobic bacteria
remove harmful chemicals in sewage treatment plants.
Anaerobic bacteria
help in the production of biogas from waste.
Microbial action reduces pollution
before water is released into rivers.
Purified water can be reused
for irrigation or other purposes.
12. Explain how microorganisms are used in the leather and textile industries.
Microorganisms play a significant role in these industries:
Leather industry
– Bacteria are used to remove hair from animal hides.
Tanning process
– Certain bacteria help in softening leather.
Textile industry
– Fungi and bacteria help in processing plant
fibres
like flax and jute.
Enzyme production
– Microbes produce enzymes used in fabric softening and dyeing.
Biodegradable dyes
– Microorganisms are used to develop eco-friendly dyes.
Waste management
– Microbes help in treating industrial waste.
13. How do microorganisms help in the preparation of medicines?
Microorganisms are used in medicine production, especially for antibiotics and vaccines.
Antibiotics
– Made using bacteria and fungi (e.g., Penicillin from Penicillium).
Vaccines
– Weakened microbes trigger immunity (e.g., Polio, Hepatitis vaccines).
Insulin production
– Bacteria are used to produce insulin for diabetics.
Antiseptics and disinfectants
– Some microorganisms help in making germ-killing substances.
Probiotics
– Beneficial bacteria in medicines improve digestion and immunity.
Cancer treatment
– Microbial enzymes are used in cancer research and drug production.
14. Describe different bacterial diseases and their prevention.
Bacterial diseases can spread through food, water, air, or physical contact.
Typhoid
– Spread through contaminated food/water; prevented by vaccination and hygiene.
Tuberculosis (TB)
– Affects the lungs; prevented by BCG vaccine and healthy living.
Cholera
– Caused by Vibrio cholerae; prevented by clean water and sanitation.
Tetanus
– Affects the nervous system; prevented by tetanus vaccine.
Pneumonia
– Causes lung infection; prevented by maintaining hygiene.
Prevention Methods
– Vaccination, sanitation, clean food and water, personal hygiene.
15. How do microorganisms contribute to global warming?
Certain microorganisms release greenhouse gases that contribute to climate change.
Methane-producing bacteria
– Found in wetlands and cattle stomachs, release methane (CH₄).
Decomposing bacteria
– Release carbon dioxide (CO₂) when breaking down organic matter.
Microbial activity in oceans
– Produces nitrous oxide (N₂O), a greenhouse gas.
Farming and livestock
– Bacteria in manure contribute to methane emissions.
Deforestation impact
– Loss of microbial diversity affects carbon absorption.
Waste management solutions
– Using biofertilizers and composting reduces harmful emissions.
16. What are the advantages of using biofertilizers?
Biofertilizers are natural fertilizers that use microorganisms to enrich the soil.
Improve soil fertility
– Bacteria like Rhizobium fix nitrogen in soil.
Eco-friendly
– Do not pollute water or soil like chemical fertilizers.
Increase crop yield
– Provide essential nutrients to plants.
Cost-effective
– Cheaper than chemical fertilizers.
Sustainable farming
– Maintains long-term soil health.
Examples
– Rhizobium,
Azotobacterial
, and Blue-Green Algae.
17. Describe how yeast helps in alcohol production.
Yeast plays a crucial role in the fermentation process to produce alcohol.
Yeast ferments sugar
to produce ethanol (alcohol) and carbon dioxide.
Used in brewing
– Beer, wine, and whiskey are made using yeast fermentation.
Baker’s yeast
– Produces carbon dioxide that makes bread and cakes fluffy.
Fermentation process
– Converts sugar into alcohol over time.
Industrial production
– Ethanol is used in medicines and fuels.
Importance
– Used in food, beverages, and biofuel industries.
18. What are the advantages of organic composting?
Organic composting is a method of decomposing waste naturally using microorganisms.
Recycles organic waste
– Converts kitchen and garden waste into compost.
Improves soil fertility
– Enriches soil with nutrients.
Reduces pollution
– Decreases landfill waste and chemical runoff.
Encourages microbial activity
– Beneficial bacteria break down organic matter.
Cost-effective
– Free alternative to chemical fertilizers.
Eco-friendly
– Promotes sustainable agriculture.
19. Explain the role of algae in oxygen production.
Algae play an essential role in producing oxygen and maintaining ecological balance.
Photosynthesis
– Algae absorb carbon dioxide and release oxygen.
Major oxygen source
– Contribute nearly
50% of Earth's oxygen
.
Support aquatic life
– Provide oxygen to marine organisms.
Algal blooms
– Can be harmful if excessive, leading to oxygen depletion.
Food source
– Algae serve as food for fish and marine animals.
Example
– Blue-green algae like Spirulina are rich in nutrients.
20. How do microorganisms help in making cheese and yogurt?
Microorganisms play a vital role in the dairy industry by fermenting milk into products like cheese and yogurt.
Bacteria like Lactobacillus
convert milk sugar (lactose) into lactic acid.
Lactic acid thickens milk
, forming curd or yogurt.
Flavour
and texture
– Different bacteria create various cheese
flavors
.
Aging process
– Some cheeses are aged with the help of fungi.
Nutritional benefits
– Rich in probiotics, which aid digestion.
Commercial importance
– Dairy industries depend on microbial fermentation.
