Class 8 Science HOTS Questions - Microorganisms-Friend or Foe

Q1: How can food be preserved by adding oil and vinegar?
Ans: 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.

Q2:  How milk is turned into curd?
Ans: 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.

Q3: How does common cold spread?
Ans: 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.

Q4: Why is tuberculosis considered as infectious disease?
Ans: 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.

Q5: What causes tuberculosis and how is it spread?
Ans: 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.

Q6: What are biological nitrogen fixers?
Ans: 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.

Q7: How can cholera be prevented?
Ans: To prevent cholera we must:

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

Q8: What are pathogens?
Ans: 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.

Q9: How do pathogens enter our body?
Ans: 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.

Q10:  Why should we not let water collect anywhere in the neighbourhood?
Ans: 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.

Q11: What will happen if we take antibiotics when not needed?
Ans: 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.

Q12: What are carriers of disease-causing microbes? Give examples.
Ans: 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.

Q13: What happens when yeast powder is added to sugar solution and kept for 4-5 hours
Ans: 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.

Q14: Why is yeast used in baking industry?
Ans: 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.

Q15: How do houseflies spread disease?
Ans: 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.

Q16: Write a short paragraph on the harms caused by microorganisms.
Ans: 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.

Q17: What is called pasteurization?
Ans: 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.

Q18: What are communicable diseases? Give examples.
Ans: 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.

Q19: Can microorganisms be seen with the naked eye? If not, how can they be seen?
Ans: 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.

Q20: Where do microorganisms live?
Ans: 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.