RBSE Class 8 Science Important Questions Chapter 2 Microorganisms: Friend and Foe

Rajasthan Board RBSE Class 8 Science Important Questions Chapter 2 Microorganisms: Friend and Foe Questions and Answers.

RBSE Class 8 Science Chapter 2 Important Questions Microorganisms: Friend and Foe

Objective Questions

Question 1.    
Name of the discoverer of vaccine for smallpox is:
(a) Edward Jenner
(b) Alexander Fleming
(c) Louis Pasteur
(d) Darwin
Answer:
(a) Edward Jenner

Question 2.    
Female Aedes mosquito is the carrier of:
(a) Malaria parasite
(b) Viruses of dengue
(c) Viruses of elephantiasis
(d) Bacteria of Cholera
Answer:
(b) Viruses of dengue

Question 3.    
Useful material for preservation of food material is:
(a) Oil
(b) Sodium benzoate
(c) Sodium metabisulphite
(d) All of the above
Answer:
(d) All of the above

Question 4.    
Which of the following is not the source of nitrogen:
(a) Protein    
(b) Nucleic acid
(c) Carbohydrate 
(d) Vitamin
Answer:
(c) Carbohydrate 

Question 5.    
Causative of rust of wheat disease is:
(a) Bacteria    
(b) Virus
(c) Algae    
(d) Fungi
Answer:
(d) Fungi

Fill in the blanks:
1. .................... are found in air, water, soil, plants and animals body.
Answer:
Microorganisms 

2. .................... produce dysentry and malaria like diseases.
Answer:
Protozoa 

3. Tuberculosis disease is .................... disease.
Answer:
communicable 

4.  Boiling kills many .................... 
Answer:
microorganisms.

True/False

Mark True (T) and False (F) on the following statements:
1. Bacteria multiply only in host.
Answer:
False

2. Curd contains several microorganisms.
Answer:
Ture

3. Louis Pasteur discovered fermentation.
Answer:
True

4. Alexander Fleming discovered the vaccine for smallpox.
Answer:
False

5. Our atmosphere has 78% oxygen gas.
Answer:
False

6. Diseases like dysentry and malaria are caused by protozoa.
Answer:
True

Match the words given in 'Column-A’ with 'Column-B':

Question 1. 

Column-A	Column-B
(i) Salt	(a) Jam
(ii) Sugar	(b) Meat and Fish
(iii) Oil	(c) Milk
(iv) Pasteurisation	(d) Pickle

Answer:

Column-A	Column-B
(i) Salt	b) Meat and Fish
(ii) Sugar	(a) Jam
(iii) Oil	(d) Pickle
(iv) Pasteurisation	(c) Milk

Question 2.

Column-A	Column-B
(i) Malaria	(a) Fungi
(ii) Polio	(b) Bacteria
(iii) Cholera	(c) Virus
(iv) Rust of wheat	(d) Protozoa

Answer:

Column-A	Column-B
(i) Malaria	(d) Protozoa
(ii) Polio	(c) Virus
(iii) Cholera	(b) Bacteria
(iv) Rust of wheat	(a) Fungi

Question 3.

Column-A	Column-B
(i) Robert Koch	(a) Penicillin
(ii) Edward Jenner	(b) Fermentation
(iii) Louis Pasteur	(c) Bacillus anthracis
(iv) Alexander Fleming	(d) Small-pox

Answer:

Column-A	Column-B
(i) Robert Koch	(c) Bacillus anthracis
(ii) Edward Jenner	(d) Small-pox
(iii) Louis Pasteur	(b) Fermentation
(iv) Alexander Fleming	(a) Penicillin

Very Short Answer Type Questions

Question 1. 
Why antibiotics are not effective against cold and flu?
Answer:
Because cold and flu are caused by viruses so antibiotics medicines are not effective on these diseases.

Question 2. 
What is the process of conversion of sugar into alochol called?
Answer:
Fermentation process.

Question 3. 
What is the causative of anthrax disease? 
Answer:
Bacillus anthracis bacteria causes anthrax disease.

Question 4. 
Give two examples of protozoa group. 
Answer:

• Amoeba 
• Paramecium 

Question 5. 
Give two examples of Algae.
Answer:

• Chlamydomonas 
• Spirogyra 

Question 6. 
What do you mean by communicable disease?
Answer:
Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.

Question 7. 
Write, die name of carrier of dengue virus.
Answer:
Female Aedes mosquito.

Question 8. 
Write the name of commonly used antibiotics produced from bacteria and fungi. 
Answer:

1. Streptomycin 
2. Tetracycline
3. Erythromycin.

Question 9. 
Write the names of any two common preservatives.
Answer:

1. Sodium benzoate 
2. Sodium metabisulphite.

Question 10. 
Which chemical is used for preservation of meat and fish?
Answer:
Salt is used.

Question 11. 
Who had discovered the pasteurisation process?
Answer:
By Louis Pasteur.

Question 12. 
What are Polio drops?
Answer:
Polio drops given to children are a vaccine.

Short Answer Type Questions

Question 1. 
Why are the fruits and vegetables spoiled when kept in open for long duration? Explain the reasons. Write any two methods to save them from being spoiled.
Answer:
When fruits and vegetables are kept in open for long duration, microorganism develop in them. These microorganism contaminate them. As a result of this vegetables etc. are spoiled.

Two methods to save them from being spoiled:

1. Some fruits and vegetables preservation can be done by salt.
2. Fruits and vegetables can be preserved by oil and vinegar.

Question 2. 
Which disease is carried by the female Aedes mosquito? Write the names of four communicable diseases?
Answer:
Female Aedes mosquito is the carrier of dengue virus.
Four communicable diseases: 

1. Cholera
2. Chickenpox 
3. Tuberculosis 
4. Common Cold.

Question 3. 
What are microorganisms? Explain. 
Answer:
Microorganisms:
These organisms are so small in size that they cannot be seen with the unaided eye. Some of these, such as fungus that grow on bread can be seen with a magnifying lens. Others can not be seen without the help of a microscope. That is why they are called microorganisms or microbes.

Question 4. 
What is virus? Explain.
Answer:
Virus:
Viruses are microscopic but they are different from other microorganisms. They multiply only in host organism, which may be a bacterium, plant or animal. Some common diseases like cold, influenza (flu) and cough are caused by viruses. Some serious diseases like polio and chicken pox are also caused by viruses.

Question 5. 
Where are micro organism found? Write.
Answer:
Micro organism can survive under all types of environment, ranging from ice cold climate to hot springs and also deserts to marshy lands. They are also found inside the bodies of animals including humans. Some micro organisms grow on other organisms while others exist freely. Micro organisms may be of both types unicellular or multicellular.

Question 6. 
How do the microorganisms help in cleaning up the environment?
Answer:
Some microorganisms play an important role in cleaning the environment. These microorganisms decompose the waste produced by us and mixed into the earth. Organic wastes (remaining of vegetables, animals wastes) are decomposed by bacteria. These bacteria are natural scavangers, which help in cleaning the environment.

Question 7. 
What is the commercial use of micro organisms? Explain.
Answer:
Commercial use of micro organisms:
Microorganisms are used for the large scale production of alcohol, wine and acetic acid. Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice, crushed fruit juices etc. Yeast can convert sugar into alcohol. 

Question 8. 
How are the antibiotics useful for animals?
Answer:
Antibiotics are helpful in preventing the different diseases in animals. Antibiotics are mixed with the food of livestock and poultry to check microbial infection in animals. Antibiotics develop immunity power in animals, which are developed by the medium of vaccine.

Question 9. 
How does the infection of causative microorganisms take place by insects and animals?
Answer:
Causative micro organisms infection:
There are some insects and animals which act as carriers of disease causing microbes. As houseflies sit on the garbage and animal excreta. Pathogens stick on their bodies. When these houseflies sit on uncovered food they transfer the pathogens. Who so ever eats the contaminated food is likely to get sick. Another example of a carrier is the female Anopheles mosquito. Mosquito is the carrier of Plasmodium (malaria parasite). Female Aedes mosquito acts as carrier of dengue virus.

Question 10. 
What do you mean by food poisoning? Explain.
Answer:
Food poisoning can be due to the consumption of food spoilt by some micro - organisms. Micro organisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So we should always use healthy and fresh food.

Question 11. 
Which are the basic steps of food preservation?
Answer:
There are two basic steps of food preservation:

1. Destroy the microorganisms and enzymes which spoil the food materials.
2. Develop such conditions which are unfit for the development and activity for microorganisms and enzymes, which spoil the food materials. 

Question 12. 
What do you mean by food preservation? Write the chemical methods for food preservation.
Answer:
Food Preservation: 
There are some substances which help to check the growth of microorganisms in food materials, they are called preservatives.

Chemical Method of Food Preservation:
We add salt or acid preservatives to pickles to prevent the attack and growth of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage. 

Question 13. 
How is the food material preserved by sugar?
Answer:
Prservation by Sugar:
Concentrated sugar solution reduces the moisture content which inhibits the growth of bacteria. So for preservation when sufficient quantity of sugar is added in the food materials, it reduces the moisture contents. Due to this very less moisture remain in the food material and the growth of bacteria, which spoil food is stopped.

Question 14. 
Explain the food preservation by salt.
Answer:
For food preservation common salt is used. To preserve meat and fish common salt is used for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.

Question 15. 
Define nitrogen fixation. Which organism does this process?
Answer:
The process of conversion of atmospheric nitrogen gas into nitrogenous compounds is known as nitrogen fixation. Atmospheric nitrogen fixation is done by organism like bacteria and algae is called ‘Biological nitrogen fixation’. The name of bacteria which does biological nitrogen fixation is Rhizobium bacteria. They live in the root nodules of leguminous plants. The algae which do biological nitrogen fixation are blue-green algae. These algae are found in the fields of paddy. 

Question 16. 
Draw a neat and clean diagram of Amoeba.
Answer:

Question 17. 
What will be the effect if all the microbes are destroyed which convert the nitrogenous compounds into nitrogen gas? Answer:
Certain bacteria convert nitrogenous compounds into nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant. If these bacteria are destroyed than the amount of nitrogen in the atmosphere will starts decreasing.

Essay Type Questions

Question 1. 
Write in tabular form the common human disease, causative microorganisms, mode of transmission and preventive measures.
Answer:
Some Common Human Diseases caused by Microorganisms

Human Disease	Causative Microorganism	Mode of Transmission	Preventive measures (General)
1. Tuberculosis 2. Measles 3. Chicken Pox 4. Polio	Bacteria Virus Virus Virus	Air Air Air/Contact Air/Water	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination should be given at a suitable age.
1. Cholera 2. Typhoid	Bacteria Bacteria	Water/Food Water	Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
Hepatitis B	Virus	Water	Drink boiled drinking water. Vaccination.
Malaria	Protozoa	Mosquito	Use mosquito net and repellents. Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings.

Question 2. 
Describe nitrogen cycle, with the help of diagram.
Answer:
Nitrogen cycle :
1. Rhizobium like bacteria lives in roots of nodules of leguminous plants do the nitrogen cycle. They fix the atmospheric nitrogen and convert into nitrogenous compounds. Some blue green algae fix nitrogen from atmosphere and convert into nitrogenous compounds.

2. Atmospheric and industrial activities also fix the atmospheric nitrogen gas. For example during lightning in the sky, atmospheric nitrogen reacts with oxygen to form nitrate, this mixes with rain water, comes on the earth and mixes with soil.

3. By biological activities the fixed nitrogen converts in plant protein.

4. Animals eat plants, the protein present in plants converts into animal protein.

5.  When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.