DAV Solutions for Class 8 Science Chapter 2
DAV Solutions for Class 8 Science Chapter 2 Microorganisms: Friends or Foes is provided here to help students in solving exercise questions provided in DAV Class 8 The living world textbook. These DAV Solutions will provide you with detailed answers to all the exercise questions. Also, these solutions comprise various types of questions such as fill in the blanks, match the following, tick the correct option, answer the following questions in brief and answer the following questions from Chapter 2 of the DAV Class 8 Science textbook.
DAV Solutions for Class 8 Science Chapter 2: After studying from this chapter’s DAV Solutions for Class 8 Science Chapter 2, students will be able to gather knowledge on microorganisms, their habitats, classes of microorganisms like bacteria, fungi, viruses and protozoans, mode of their reproduction, harmful microorganisms, use of microorganisms, pathogens, soil microorganisms, nitrogen fixation by bacteria. The DAV Solutions for Class 8 Science provided here are helpful for the students to clear all their doubts in the chapter in an easy and interesting way.
DAV Class 8 Science Chapter 2 Question Answer
DAV Solutions for Class 8 Science Chapter 2 Microorganisms: Friends or Foes is given below. Here DAV Class 8 Science Chapter 2 Question Answer is provided with great explanation.
- A. Fill in the blanks.
- B. Match the following.
- C. Tick the correct option.
- D. Answer the following questions in brief.
- E. Answer the following questions.
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1. The study of microorganisms is known as ___________.
2. The bread dough rises because of the production of ___________.
3. ___________ are the microorganisms that cause diseases.
4. ___________ and ___________ are two chemical preservatives.
5. ___________ is a fungus that causes food poisoning.
Answer: (1) microbiology (2) carbon dioxide (3) pathogens (4) sodium benzoate, potassium metabisulphite (5) Aspergillus
Answer: (1) c, (2) a, (3) d (4) e (5) b
1. The process, that helps milk to last longer but does not kill all microbes present in it, is known as-
2. Rust of wheat is caused by-
3. Medicines, containing killed or weakened pathogens, and used to prevent infectious diseases, are called-
4. Which of the following reproduces only inside a host cell?
5. A disease, caused by a virus, and spread by an insect, is-
1. Why are viruses considered as being at the ‘borderline’ between living and non-living things?
Answer: A virus behaves like a non-living when it is outside a host cell. Once a virus enters a host cell, it starts to behave like a living being. Due to this, viruses are considered as the borderline between living and non-living.
2. What is fermentation? How is this process useful in the food and beverage industries?
Answer: An anaerobic process through which sugars/carbohydrates are converted into alcohol or acids and carbon dioxide by microorganisms is called fermentation.
Fermentation is useful in the food and beverages industries in various ways:
- It helps in making tasty dosa.
- It helps in making bread and cake.
- It helps in making wine
3. ‘In the absence of microorganisms the earth would become a heap of dead plants and animals. Justify this statement.
Answer: When a plant or animal dies, its remains are decomposed by microorganisms. Decomposition is the process through which all constituent materials of a living being are sent back to the environment. Had there been no microorganisms, dead remains of plants and animals would be keeping on accumulating all around us. So, it can be said that in the absence of microorganisms the earth would become a heap of dead plants and animals.
4. Munna observes that the yield of wheat, growing in his field, has reduced in the current year. He gets the soil tested and the report confirms the deficiency of one particular nutrient. Accordingly, he is advised to grow peas after harvesting wheat.
(i) Name the nutrient found insufficient.
(ii) How do you think growing peas will help in replenishing the soil?
Answer: Pea plants give shelter to Rhizobium bacteria. These bacteria carry out nitrogen fixation in soil. Thus, pea plants help in replenishing nitrogen in soil.
5. Why does it take less time to prepare curd in summers as compared to preparing it in winters?
Answer: Microorganisms reproduce at a faster rate between 20 to 40°C. They reproduce at a much slower rate when temperature is below this range. Milk is converted into curd by multiplication of lactobacillus. This is why it takes less time to prepare curd in summers as compared to preparing it in winters.
6. How are the following diseases transmitted:
(a) Malaria (b) Common cold (c) Tetanus (d) Typhoid
Answer: (a) By female Anopheles mosquito.
Answer: (b) Through cough droplets in air.
Answer: (c) Through cut by a rusted iron article.
Answer: (d) Through contaminated food and water.
7. What are antibiotics? How are they produced? Give two examples of these.
Answer: Antibiotics are chemicals that inhibit the growth of (other) harmful microorganisms by affecting their life processes. Antibiotics are prepared from microorganisms. Two examples are Penicillin and Streptomycin.
1. ‘Microorganisms are very useful in manufacturing different food items’. Explain the above statement.
Answer: Microorganisms are very useful in manufacturing different food items in various ways. They are used in making tasty dosa. It helps in making bread and cake. Many microorganisms are used in the manufacture of alcohol, wine and acetic acid.
2. Give reasons for the following.
(a) Yeast is added to the batter used to make ‘dosas’.
Answer: Yeast is added to the batter so that fermentation take place. It causes it to increase in volume and makes it fluffy and soft.
(b) It is important to brush one’s teeth before going to bed.
Answer: It is important to brush one’s teeth before going to bed because bacteria can grow on food particles that get lodged in between our teeth. Acid produced by these bacteria, corrode the tooth enamel and cause cavities. Hence it is important to brush one’s teeth before going to bed.
(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
Answer: Salt reduce the water content of pickle and make it unavailable for the growth of microorganisms. As the result pickle gets preserved. If the quantity of salt is reduced then it increases the growth of microorganisms and can it to go bad soon.
(d) Foods, from puffed or enlarged cans, should not be consumed.
Answer: Enlarged or puffed can represent that there had been some bacterial action on the item which might lead to formation of toxic substance.
(e) When using frozen food items, one should take out only the required quantities; thawed food should never be refrozen.
Answer: One should take out only required quantity of frozen food as it might spoil the rest of food item and refrozing the frozen item destroys its nutrients.
3. How do communicable diseases spread? Suggest ways to prevent the following diseases:
(a) Tuberculosis (b) Athlete’s foot (c) Cholera
Answer: Communicable diseases spread from one person to another through air, water, food, physical contact or insects.
(a) Tuberculosis- It can be prevented by vaccination.
(b) Athlete’s foot- It can be prevented by maintaining good personal hygiene.
(c) Cholera- Cholera can be prevented by proper disposal of waste and using disinfected water.
4. What are pathogens? Name two pathogens each that cause diseases in (i) plants and (ii) animals.
Answer: Some microorganisms cause diseases in human beings, plant and animals. Such diseases causing organisms are known as pathogens.
Bacteria and Fungi are the examples of pathogens which cause diseases in plants and animals.
5. Mohan bought samosas from a road-side vendor and ate it. After sometime he felt nausea and started vomitting. He had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for his condition? What is it called? How could it be prevented?
Answer: This could happen due to consumption of contaminated food. This disease is called food poisoning. Food must be properly prepared and stored to prevent food poisoning.
6. Which diseases the following children are most likely to suffer from?
(a) Ramu drinks water from a nearby lake. This water is neither boiled nor disinfected.
(b) Ashu does not take a bath every day. He maintains poor personal hygiene.
(c) Pulkit has been bitten by an infected street dog.
(d) Sohan is living in an area where the population is very high. He does not use a mosquito net (while sleeping), or insect-repellent creams (while playing in the open).
(e) Mohan was with two of his friends who were coughing and sneezing (they were suffering from common cold). One of these friends did not keep a handkerchief in front of his mouth while coughing and sneezing.
Answer: Common cold.