DAV Class 8 Science Solution Chapter 2 Microorganisms: Friends or Foes
DAV School Books Class 8 Science Solution Chapter 2 Microorganisms: Friends or Foes all Question Answer. DAV Class 8 2nd Chapter Microorganisms: Friends or Foes full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 2 Microorganisms: Friends or Foes:
A.) Fill in the blanks.
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
B.) Match the following
1. Ringworm | a. Food poisoning |
2. Clostridium | b. Biogas reactor |
3. anthrax | c. Fungus |
4. lactobacillus | d. Cattle |
5. methane | e. Curd |
Answer: (1) c, (2) a, (3) d (4) e (5) b
C.) Tick the correct option.
1.) The process, that helps milk to last longer but does not kill all microbes present in it, is known as-
Answer: pasteurisation
2.) Rust of wheat is caused by-
Answer: fungus
3.) Medicines, containing killed or weakened pathogens, and used to prevent infectious diseases, are called-
Answer: vaccines
4.) Which of the following reproduces only inside a host cell?
Answer: virus
5.) A disease, caused by a virus, and spread by an insect, is-
Answer: dengue
D.) Answer the following questions in brief.
1.) Why are viruses considered as being at the ‘borderline’ between living and non-living things?
Viruses have an unique character, while it is outside any host cell it behaves as a non living organism and can also be crystallised and stored in jars. However when they come in contact with suitable living hosts, the virus infects it and takes full control over its cell and thereby starts to multiply itself , thus showing the characteristics of living organisms.
2.) What is fermentation? How is this process useful in the food and beverage industries?
Fermentation is a process in which microorganisms during reproduction release carbon dioxide as well as Convert Sugars into carbohydrate as well as alcohols and acids. Usually the process of fermentation is used in the food industry such as in the making of those and Bakery products .The alcohol industry is also dependent on fermentation since products like wheat and Barley ferment to produce alcoholic beverages.
3.) ‘In the absence of microorganisms the earth would become a heap of dead plants and animals. Justify this statement.
Various microorganism help in decomposition of date and the king matter without them any dead and decaying matter would not be decomposed and it would not give us any organic material instead it would be a heap of garbage.
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.
Nitrogen
(ii) How do you think growing peas will help in replenishing the soil?
Rhizobium bacteria are protected by pea plants. In soil, these microorganisms fix nitrogen. Thus, pea plants contribute to the renewal of nitrogen in the soil.
5.) Why does it take less time to prepare curd in summers as compared to preparing it in winters?
The temperature in summer is ideal for the growth of microorganisms as well as the humidity. As a result, microorganisms such as lactobacillus can help create curd from milk.
6.) How are the following diseases transmitted:
(a) Malaria – female Anopheles mosquito.
(b) Common cold- cough droplets suspended in air.
(c) Tetanus-cut caused by a rusted iron article.
(d) Typhoid-by consuming contaminated food and water.
7.) What are antibiotics? How are they produced? Give two examples of these.
Antibiotics are chemicals that prevent the growth of certain microorganisms which are harmful for human body .antibiotics are produced by using dead or weakened microorganism .penicillin and antibiotic is prepared from a fungus known as Penicillium notatum, streptomycin is another commonly used antibiotic.
E.) Answer the following questions.
1.) ‘Microorganisms are very useful in manufacturing different food items’. Explain the above statement.
Microorganism are used to produce various food items such as curd or cheese as well as different Bakery products it is also used in different alcoholic beverage making due to the process of fermentation microorganisms such as East and fungus produce carbon dioxide acetic acid which helps in the production of Bakery products in various ways..
2.) Give reasons for the following.
(a) Yeast is added to the batter used to make ‘dosas’.
In the process of making dosa yeast is added to the better so that the anaerobic respiration of the east cells can produce carbon dioxide that helps to make the batteries make it more volume less and give it a good texture and consistency
(b) It is important to brush one’s teeth before going to bed.
The food particles stuck into the gaps of teeth attract bacterias that can damage the enamel and cause cavities.
(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
Process of pickle making includes adding salt so that it can prevent the growth of different micro organisms that can spoil it
(d) Foods, from puffed or enlarged cans, should not be consumed.
Foods are stored in puffed and enlarged cans are usually deemed unfit because there are high chances that they may have undergone the action of microbial growth which might be harmful
(e) When using frozen food items, one should take out only the required quantities; thawed food should never be refrozen.
Only sufficient amount of food should be taken out of the freezer because coming in contact with the air outside rest of the food might be subjected to microbial invasion and deplete the foot of its nutrients
3.) How do communicable diseases spread? Suggest ways to prevent the following diseases:
(a) Tuberculosis-prevented by vaccination.
(b) Athlete’s foot- prevented by maintaining good personal hygiene.
(c) Cholera-prevented by proper disposal of waste and using disinfected water and clean water.
4.) What are pathogens? Name two pathogens each that cause diseases in (i) plants and (ii) animals.
Pathogen are the agents that carry microorganism causing diseases
Bacteria and fungi are two pathogens that cause diseases in both 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?
This might occur as a result of eating spoilt food. Food poisoning is the name of this illness. Food poisoning must be avoided by properly preparing and storing food.
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.
Cholera
(b) Ashu does not take a bath every day. He maintains poor personal hygiene.
Ringworm
(c) Pulkit has been bitten by an infected street dog.
Answer: Rabies
(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).
Answer: Malaria
(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.
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