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CBSE Sample Paper Class 8 Science Microorganisms Friend and Foe
Microorganisms Friend and Foe
1.) Answer the short questions (10×1)
a.) Write the groups in which microorganisms are classified into?
b.) Name some diseases caused by viruses.
c.) Which diseases are caused by protozoa?
d.) Which bacteria helps us to make curd?
e.) List the uses of yeast.
f.) What is fermentation?
g.) Who discovered penicillin?
h.) What are antibiotics?
i.) What are pathogens?
j.) What are preservatives?
2.) Briefly answer the questions (3×10)
a.) How viruses are different from other microorganisms?
b.) How microorganisms help us and environment?
c.) Why yeast is used in baking?
d.) How penicillin was prepared?
e.) How vaccines work?
f.) Briefly describe how microorganisms helps to clean the environment?
g.) How communicable diseases are spread?
h.) List and briefly explain the methods of food preservation.
i.) Describe the pasteurization process.
j.) Briefly describe the nitrogen cycle.
3.) Fill in the blanks (5×1)
a.) When diseases causing microbes enter our body, our body produces _________ .
b.) ________ discovered the vaccine for small pox.
c.) ________ has been eradicated from the most part of the world.
d.) Bacterium which cause anthrax disease was discovered by _________ .
e.) Female _______ mosquito acts as a carrier of dengue virus.
(4) Complete the list
Disease name |
Causative microorganisms | Mode of transmission |
Chicken pox |
|
|
Cholera |
||
Malaria |
|
|
Tuberculosis |
||
Hepatitis A |
|
Answer
1.) Answer the short questions (10×1)
a.) Write the groups in which microorganisms are classified into?
Answer – Microorganisms are classified into bacteria, fungi, protozoa and algae.
b.) Name some diseases caused by viruses.
Answer – Diseases such as influenza, cold and most coughs are caused by viruses.
c.) Which diseases are caused by protozoa?
Answer – Typhoid and tuberculosis are caused by protozoa.
d.) Which bacteria helps us to make curd?
Answer – Lactobacillus helps us to make curd.
e.) List the uses of yeast.
Answer – Yeast is used for making bread, pastries, cakes and used to produce alcohol and wine.
f.) What is fermentation?
Answer – Sugar is converted to alcohol by yeast. This process of converting sugar into alcohol is called fermentation.
g.) Who discovered penicillin?
Answer – Alexander Fleming discovered penicillin.
h.) What are antibiotics?
Answer – Antibiotics is a type of medicine which prevent the growth or kill disease-causing microorganisms.
i.) What are pathogens?
Answer – Some microorganisms cause diseases in our body, these disease-causing microorganisms are called pathogens.
j.) What are preservatives?
Answer – Chemicals, such as oil and salt, which prevent microorganisms from attacking our food and stop spoilage, are called preservatives.
2.) Briefly answer the questions (3×10)
a.) How viruses are different from other microorganisms?
Answer – Virus are also microorganisms but they are different from other microorganisms. Unlike other microorganisms such as bacteria, fungi, protozoa and algae, it shows non-living characteristics outside cells of living organism and show living characteristics inside it and also they only reproduce inside living cell.
b.) How microorganisms help us and environment?
Answer – Microorganisms helps us to make bread, cake, curd, alcohol and helps the environment by breaking down organic waste into harmless and usable substances. In agriculture microorganisms help us to increase soil fertility.
c.) Why yeast is used in baking?
Answer – Yeast is added when the dough is made for baking. In the dough yeast reproduces rapidly and in this process release carbon dioxide by respiration. This produces bubbles in the dough which increases its volume. This is the reason yeast is used for baking.
d.) How penicillin was prepared?
Answer – Penicillin was found by Alexander Fleming. In 1929, he was working on a culture which was containing disease-causing bacteria. But accidentally he left it behind. After he came back he found out some spores of green mould in the culture plate. He observed that the presence of the mould prevented the growth of the bacteria. Penicillin was prepared from this mould.
e.) How vaccines work?
Answer – When disease-causing microbes enters in our body our body produces antibodies to protect us and kill the microbes. If the same microbe again enters our body, the previous antibodies can easily prevent it from causing disease.
Vaccine use this mechanism for our advantage. Vaccines contain dead or weakened microbes which do not cause severe disease but triggers immune response in our body. After that body produces antibodies and kill the microbes and stay in our body and protect us form that disease for ever.
f.) Briefly describe how microorganisms helps to clean the environment?
Answer – Microorganisms are essential for our environment. Microorganisms decompose dead animal and plants. They convert organic waste into harmless and simple substances. This process helps the environment to stay clean as well as the substances produced by the decomposition helps the plants with nutrients.
(g) How communicable diseases are spread?
Answer – Communicable diseases are the disease which can spread from infected person to a healthy person. Communicable disease can spread in lots of ways. Some of the ways are,
- Through the air we breath.
- Through the water we drink.
- Physical contact.
- Food
(h) List and briefly explain the methods of food preservation.
Answer – Food are preserved by the methods including,
- Chemical method
Preservatives are used for this method of preservation.
- Preservation by common salt
Common salt has been used for preserving meat and fish for ages. Salt prevents the bacterial growth.
- Preservation by Sugar
Sugar is used for preservation because it reduces the moisture content of food.
- Preservation by Oil and Vinegar
Oil and vinegar prevents bacterial growth because bacteria cannot live in such environment.
- Heat and cold method
Heating kills microorganisms and cold environment inhibits growth of the microbes.
(i) Describe the pasteurization process.
Answer – Pasteurization process was discovered by Louis Pasteur. This process is used to sterilize milk. In this process milk is heated for 70°C for 15 to 30 minutes, then followed by quick cooling. Then it is stored. This process prevents the growth of bacteria.
(j) Briefly describe the nitrogen cycle.
Answer – Nitrogen is an essential component of all living organisms. Nitrogen is a part of proteins. Though it is available in a vast quantity, we cannot utilize it directly from the atmosphere. Some bacteria and blue green algae present in soil convert atmospheric nitrogen into nitrogen compounds, which are then utilized by plants and animals get nitrogen by eating plants. When plants and animals die microorganisms decompose them And convert nitrogenous waste into nitrogen compound. This compound are again utilized by plants. This process is called nitrogen cycle.
(3) Fill in the blanks (5×1)
(a) When diseases causing microbes enter our body, our body produces antibodies.
(b) Edward Jenner discovered the vaccine for small pox.
(c) Small pox has been eradicated from the most part of the world.
(d) Bacterium which cause anthrax disease was discovered by Robert Koch.
(e) Female aedes mosquito acts as a carrier of dengue virus.
(4) Complete the list
Disease name |
Causative microorganisms | Mode of transmission |
Chicken pox | Virus |
Air and contact |
Cholera |
Bacteria | Water and food |
Malaria | Protozoa |
Mosquito |
Tuberculosis |
Bacteria | Air |
Hepatitis A | Virus |
Water |