Monday, 11 June 2018

CBSE Class 8 - Science - Microorganisms - Friends Or Foes (Questions and Answers) (#cbsenotes)(#eduvictors)

Microorganisms – Friends or Foes (Q & A-2)

Class 8 – Science – Microorganisms – Friends or Foes (Worksheet) (#cbseNotes)

Q1: Fill in the blanks:
a. Microorganisms may be unicellular or ___________.

b. __________ bacteria help to make curd from milk.

c. Disease-causing microorganisms are called _______.

d. Ammonium salt in the soil is converted first into nitrites by _________ bacteria.

e. _______ coagulation takes place only when milk is hot.

f. Salting draws out _______ from food.

g. Nitrate in the soil is converted by _________ bacteria into nitrogen gas.

h. The process of preventing food spoilage by chemical or physical methods is called food ________.

a. Multicellular
b. Lactobacillus
c. pathogens
d. Nitrifying
e. Casein
f. water
g. denitrifying
h. preservation

Q2: Name any two antibiotics.

Answer: Penicillin, streptomycin, tetracycline

Q3: Give the names of any two communicable diseases.

Answer: Malaria, Typhoid

Q4: What are the two common food preservatives used in our homes?

Answer: Salt, sugar and oil.

Q5: Name the bacteria that are present in root nodules of leguminous plants that fix nitrogen.

Answer: Rhizobium

Q6: Very often we observe greenish pond water in our surroundings. What type of microbes they are likely to be?

Answer: Alga

Q7: Name two microbial diseases which spread through air,

Answer: Common cold, flu, tuberculosis, influenza, smallpox

Q8: Name any unicellular algae.

Answer: Cyanobacteria

Q9:  Name three diseases caused by a virus in humans

Answer: Common cold, Hepatitis, HIV, Swine flu, Polio

Q10: Which organisms are interlinked between living and non-living organisms?

Answer: Virus

Q11: What is pasteurisation?

Answer: The process in which milk is heated up to 72°C for 15 to 30 minutes and then chilled and stored is called pasteurization. This prevents the growth of most microorganisms.

Q12: Pasteurisation led to another process, critical to surgery. Name the process.

Answer: Sterilisation.

Q13: What are the advantages of food preservation?

Answer: Proper preservation of food (e.g. cold storage) helps us, in the following ways:
1) This prevents spoilage of food.
2) Food can be preserved for a longer period.
3) Quality of food is ensured for a long time.
4) Variety of food items may be available in faraway places, in any season.

Q14: How do microbes cause food poisoning?

Answer: Some microbes release toxins in improperly preserved food, which causes food poisoning. e.g. Clostridium botulinum and Salmonella are the common bacteria that cause food poisoning.

Q15: How do leguminous plants increase the soil fertility?

Answer: Leguminous plants provide shelter to Rhizobium bacteria in their root nodules that help in converting atmospheric nitrogen present in soil into a usable form that is taken by plants to make plant protein.

Q16: What is meant by nitrifying bacteria?

Answer: Bacteria which help to convert ammonia present in soil into nitrates is called nitrifying bacteria.

Q17: How does female Anopheles mosquito spread malaria?

Answer: Female Anopheles mosquito carries the malaria germ. When it bites a healthy person, he/she can get infected with malaria.

Q18: How do antibiotics work?

Answer: Antibiotics kill or stop the growth of disease-causing microbes.

Q19: What are antibodies?

Answer: Whenever a disease-causing microorganism enter our body, the body produces some defenders to fight against them, these are called as antibodies. Antibodies fight the disease-causing microorganisms.

Q20: How do viruses differ from other microorganisms?

Answer: A virus is a microorganism which exhibits characteristics of living as well as non-living things.

Q21: What is fermentation?

Answer: The conversion of sugar into alcohol in absence of oxygen by the action of yeast is called fermentation.

Q22: What the uses of fermentation process?

Answer: This process is used on a large scale in the production of alcohol, wine, beer and acetic acid.

Q23: Explain the formation of curd from milk.

Answer: Milk contains a type of sugar called lactose. When milk is heated to the temperature of 30-40°C and a small amount of sour curd added to it, the lactobacillus bacteria present in the curd starts growing and convert the lactose into lactic acid. Thus milk is converted into curd.

Q24: What is a vaccine? How does it work?

Answer: Vaccines are the substances used to produce immunity to diseases in the living body.

The vaccine contains dead or weakens microbes. When these are swallowed or injected into the body of a patient, the body produces antibodies to fight them. Antibodies remain in bodies and protect it from any future attack disease-causing microorganism

Q25: Why should we use antibiotics only after the advice of a doctor?

Answer: We must use antibiotics prescribed by a qualified doctor. If you use antibiotics without consulting a qualified doctor it may harm you. Unnecessary use of antibiotics affects blood cells which fight infections. Sometimes they may kill useful bacteria too in our intestine and this increases the resistance towards antibiotics. Excess use of antibiotics weakens the body.

Q26: Microorganisms decompose dead organic waste of plants and animals and help in keeping the environment clean. What would happen, if microorganisms do not perform this function?

Answer: Air, water and soil get polluted if microorganisms do not decompose dead organic waste of plants and animals

Q27: Describe the principle on which the following methods of food preservation are based:
(a) boiling 
(b) canning 
(c) freezing 
(d) dehydration

(a) boiling: Heating to food at high temperature kill bacteria.
(b) Canning: canning stops the supply of oxygen to bacteria and stop its growth.
(c) freezing: it lowers the temperature that reduces the growth of bacteria
(d) Dehydration: it forces bacteria to lose water by osmosis and stop growing further.

Q28: Why should we always wash our hands before handling food items?

Answer: We should always wash our hands before eating to prevent the germs in our hands from entering the food so that we are prevented from getting diseases.

Q29: What diseases can be prevented if we control mosquitoes?

Answer: Dengue, Malaria, Chikangunia, Zika,Japanese Encephalitis

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