Class 8 - Questions and Answers Ch-2 Microorganisms

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ORAL QUESTIONS

1. All microbes are harmful. Do you agree? Give reasons.

Ans. No, all the microbes are not harmful to us because few microorganisms like lactobacillus bacteria helps in formation of curd, rhizobium bacteria which is present in roots of leguminous plants help in fixing of atmospheric nitrogen in the soil and many more.

2. Name the type of microorganisms that:

a. have chlorophyll: Algae b. do not have a cellular structure: Viruses

3. Give one property because of which viruses are regarded as being on the borderline of living and non-living.

Ans. Viruses are considered as non-living organisms outside the living cell because they cannot reproduce by themselves, respond to changes and grow. However, when a virus enters the living cell of an organism, it is able to reproduce by using the energy from the host cell.

4. Which one is closer to plants - algae or protozoa? In what aspect?

Ans. Algae is closer to plant because it has cell walls and chlorophyll within the cell, they prepare their own food by photosynthesis like plants whereas protozoa have animal like characteristics .

5. Where do you normally expect to find algae- in the soil, in a pond or in the air?

Ans. Almost all algae live in water - in ponds, lakes and seawater.

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Oral Questions

1. While making cake and dokhla, the dough rises because of the substance that is produced during fermentation. What substance is this? Why does it cause the dough to rise?

Ans. While making cake and dhokla, bakers add yeast to make it fluffy because during the fermentation yeast uses sugar from food to form alcohol and carbon dioxide gas is given off. Carbon dioxide gas increases the volume of the dough.

2. To prevent a diseases caused by a certain microbe, doctor's inject the same microbes in a person's blood. How is it ensured that this prevents the disease instead of causing it? What is this process if injecting microbes called?

Ans. Vaccines consists of dead or weakened microbes. When injected in a person's blood, the body produces antibodies to fight them.The antibodies remain the body and protect the person from any future attack. The body is said to be immunized against disease and the process is called immunization.

3. Microbes that live inside the bodies of animals normally cause diseases. However some of them also help animals. Give an example to prove this point.

Ans.a) In digestive system of certain herbivorous animals such as goats and cows, houses certain beneficial protozoa and bacteria. These microbes help herbivorous to digest plant materials by breaking down cellulose.

b) lactobacillus bacteria which is present in curd also inhibit the growth of illness causing bacteria inside the intestinal tract and promote beneficial bacteria needed for digestion.

4. Pasteurization means boiling the milk to kill germs. Do you agree? Give reasons.

Ans. Pasteurization is a food preservation technique, in which the milk is firstly heated to a temperature of 70ºC. Afterwards, the milk is rapidly cooled down to prevent the growth of microbes. Thus, pasteurization is not just boiling the milk to get rid of germs.

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EXERCISES

A. Choose the most appropriate answer.

1. Which of the following cannot be classified as either living or non-living?

a. fungi b. bacteria c. viruses d. protozoa

Ans. c. Viruses

2. Amoeba ia a

a. bacterium b. virus c. fungus d. protozoa

Ans. d. protozoa

3. Which of the following make their own food by photosynthesis?

a. algae b. viruses c. fungi d. protozoa

Ans. a. algae

4. The unicellular organisms that sour milk to make curd are

a. bacteria b. viruses c. fungi d. protozoa

Ans. a. bacteria(lactobacillus)

5. Which of the following is responsible for making bread soft and fluffy?

a. finely ground flour

b. sugar

c. alcohol given off during fermentation of sugar

d. carbon dioxide gas given off during fermentation of sugar

Ans. d. carbon dioxide gas given off during fermentation of sugar

6. Which of these do not have a regular cell structure?

a. bacteria b. viruses c. algae d. protozoa

Ans. b. viruses

7. Which of these are found as both unicellular and multicellular organisms?

a. bacteria b. viruses c. algae d. protozoa

Ans. c. algae

8. The bacterium lactobacillus is useful in making

a. cheese b. cake c. alcohol d. all of these

Ans. a. cheese

9. Microorganisms spread through

a. air b. cuts c. water d. all of these

Ans. d. all of these

10. Which of these does not prevent growth of bacteria?

a. salt b. sugar c. water d. oil

Ans. c. water

B. VERY SHORT - ANSWER QUESTIONS: Give one word answers.

1. What is the study of microorganisms known as?

Ans. Microbiology

2. Microbes are disease - causing microorganisms? True or false?

Ans. False because disease causing microbes are called pathogens or germs.

3. All the fungi are unicellular. True or false?

Ans. Flase. Fungi can be both unicellular(yeast) and multicellular(bread mould).

4. Under unfavourable conditions, microorganisms form a ______ around themselves.

Ans. Cyst(hard covering)

5. What are spherical bacteria called?

Ans. Cocci

6. A virus can reproduce on its own. True or false?

Ans False

7. Where are algae mostly found - in water or on land?

Ans. In water

8. Is the decomposition of the bodies of dead plants and animals by microorganisms desirable or undesirable?

Ans. Desirable because it helps in cleaning the environment.

9. Name the class of medicines usually made from fungi or bacteria that can cure dangerous diseases.

Ans. Antibiotics

10. Is yeast bacterium or fungus?

Ans. Fungus

11. The female Aedes mosquito is a carrier of the _____ virus.

Ans. Dengue

12. The foot and mouth disease is caused by a ______

Ans. Virus

13. Food poisoning is caused by a toxin getting accidentally mixed with food. True or false?

Ans. False

14. What is heating milk to high temperature and then cooling it quickly called?

Ans. Pasteurization

15. Salt forces the microbes to lose water. True or false?

Ans. True