Microorganisms: Friend and Foe Class 8 Extra Questions Science Chapter 2
Microorganisms: Friend and Foe Class 8 Extra Questions Very Short Answer Questions
Name the groups in which microorganisms are broadly classified.
Microorganisms are broadly classified in four groups:
Name the type of microorganism that is smaller than bacteria.
Write the name of a bacterium that helps in the formation of curd.
Write a use of yeast.
Yeast is used in the production of alcohol, wine, beer and other beverages.
What does yeast produce during respiration?
Yeast produces carbon dioxide gas during respiration.
What are pathogens? Write another name of pathogens.
Disease-causing microorganisms are known as pathogens. They are also called germs.
Define food preservation.
Food preservation is the method of preserving food from being spoiled by the microbes.
Write the names of any two antibiotics.
Who discovered the vaccine for small pox?
What is fermentation?
Fermentation is the process of conversion of food into alcohol.
The storing of food products at the temperature of 0°C to 5°C is known as refrigeration.
What is vaccine?
A substance which is used in the production of immunity against various diseases in the living body is termed as vaccine.
Name any two human diseases caused by viruses.
Name any three common plant diseases.
Rust of wheat, citrus canker and wilt
Name a microorganism which helps in nitrogen fixation.
Name a disease caused by food poisoning.
What is the difference between refrigeration and freezing?
In refrigeration, the storing of the food is done at a temperature of 0°C to 5°C, whereas freezing is used to store food at -18°C of temperature.
What is decomposition?
Decomposition is the process in which organic materials are broken down into simple inorganic sub-stances by the microorganisms.
Name the two microbes that are involved in the process of decomposition.
Bacteria and fungi
Name the first antibiotic discovered.
Microorganisms: Friend and Foe Class 8 Extra Questions Short Answer Questions
What are microorganisms? Give four examples.
Small organisms that cannot be seen through the naked eyes and can only be seen under a microscope are called microorganisms or microbes; e.g., Amoeba, Paramecium, Volvox, Spirogyra, etc.
Classify bacteria on the basis of their shapes.
On the basis of their shapes, bacteria are classified into four categories:
- rod-shaped bacteria (bacilli)
- spherical-shaped bacteria (cocci)
- curved-shaped bacteria (vibrios)
- spiral-shaped bacteria (spirilla)
Define communicable diseases. Give some examples.
Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, or other physical contacts; e.g., cholera, chicken pox, tuberculosis, common cold, etc.
Differentiate between viruses and other microorganisms.
|(i) They show the characteristics of living organisms or reproduce only by entering the host organisms.||(i) They do not need to enter any host organism to reproduce or show any characteristics of life.|
|(ii) They are non-cellular microbes.||(ii) They are cellular microbes.|
What do you mean by food spoilage?
The process in which food is deteriorated to such extent that it does not remain fit for human consumption is known as food spoilage.
What role does sugar play in the preservation of food?
The role of sugar in food preservation is significant. By adding sugar in the food item, we reduce its moisture content and hence, it stops the growth of the microorganisms.
How are carriers harmful to us?
Carriers take with them many harmful microorganisms or pathogens. They play a great role in transferring these pathogens to a healthy person, by sitting on the food items, or directly transferring the pathogens inside the body of a person. Hence they are harmful to us.
What is vaccination?
The process of putting a vaccine inside the body of a person in order to produce immunity against some disease is called vaccination.
What do you mean by immunity?
Immunity is the ability of a body to develop resistance against diseases.
Give two examples of each of the following types of microorganisms:
(a) Algae – Spirogyra, Chlamydomonas
(b) Fungi – Aspergillus, yeast
(c) Protozoa – Paramecium, Amoeba
What are antibodies?
Whenever any harmful disease-causing microorganism enters the human body, the body produces substances to fight with the entered microbe. These substances are called antibodies.
What is the role of bacteria in increasing the soil fertility?
Some bacteria, which are present in the root nodules of leguminous plants or free-living fix the atmospheric nitrogen in the soil which is ultimately used up by the plants. Hence they increase the fertility of the soil. For example, Rhizobium, Azotobacter, Azospirillum, etc.
Define Ohmic heating.
Ohmic heating is the process in which electric current of high voltage is passed through the food items to kill the microbes that cause the spoilage of food.
What is sterilisation?
The process of killing all the microorganisms above the temperature of 100°C is known as sterilisation. It is one of the widely used methods to preserve food, and is often used for various food items.
What is pasteurisation?
Pasteurisation can be defined as the partial sterilisation of foods at a temperature that destroys harmful microorganisms without major changes in the chemical property of the food.
Microorganisms: Friend and Foe Class 8 Extra Questions Long Answer Questions
Explain why antibiotics do not work against flu or any infection caused by viruses.
Viruses cannot be killed by using antibiotics as their cell pathways are different from that of bacteria. It means taking antibiotics to get rid of flu or any other viral infection is useless, because it does not re-duce the strength of the virus, nor does it reduce the duration of the infection. But, however, antibiotic will work if we get attacks of viral infection and bacterial disease at the same time. Even then, it will cure bacterial disease only but not the viral infection.
Mention any three ways through which pathogens are transmitted.
Three ways because of which pathogens are transmitted are as follows:
- When a person sneezes or coughs, tiny droplets containing a number of disease-causing microorganisms come out of the mouth, and are released in the air. They are transmitted to a healthy person while breathing.
- By making direct contacts with an infected person, pathogens are transferred to a healthy person.
- Carriers of pathogens also help in their transmission. For instance, when a fly sits on animal excreta or garbage, harmful disease-causing microbes stick to its legs. And when this fly sits on the food items, pathogens get transferred to them. This contaminated food items cause serious diseases when it is eaten by a healthy person.
Canning is a process used for food preservation. Heat, at a certain temperature and for a limited period of time, is used to kill the harmful microorganisms as well as enzymes. This method also involves the removal of oxygen gas, and to avoid post-process contamination by airtight sealing of food items.
Explain how malaria is transmitted to humans.
A protozoan called Plasmodium is responsible for malaria. It lives in the liver and blood of the person who has been infected by this disease. A female Anopheles mosquito when sucks blood from the infected person, Plasmodium along with blood, is taken into its stomach. The Plasmodium, here, multiplies itself and reaches the salivary gland of the mosquito. Now, when this mosquito bites a healthy person, it injects Plasmodium along with saliva to him. The healthy person then gets an attack of malaria.
In this way, malaria is transmitted to humans.
Explain various types of bacteria.
Bacteria are classified on the basis of their shapes into the following categories:
- Rod-shaped bacteria (bacilli):
These are aerobic rod-shaped, spore-producing bacteria. They are often occurring in chain-like formations, and they are found primarily in soil; e.g., Lactobacillus.
- Spherical-shaped bacteria (cocci):
They are spherical or nearly spherical bacteria; e.g., Streptococcus.
- Curved-shaped bacteria (vibrios):
They are curved-shaped bacteria; e.g., Vibrio.
- Spiral-shaped bacteria (spirilla):
They are flagellated, aerobic bacteria, having a spirally twisted rod-like form; e.g., Treponema.
Microorganisms: Friend and Foe Class 8 Extra Questions Higher Order Thinking Skills
Unscramble the jumbled words underlined in the following statements
(a) Curbossulite is an air-borne disease caused by a bacterium.
(b) Xanrhat is a dangerous bacterial disease.
(c) Yeasts are used in the wine industry because of their property of meronettinaf.
(d) Cells of our body produce santiidobe to fight pathogens.
(e) Aeeessrrwtip are added to food to prevent growth of microorganisms.
What is the difference between Rhizobium and cyanobacteria in the way of fixing nitrogen for the plants?
Rhizobium lives in the root nodules of leguminous plants in a symbiotic relationship whereas cyanobacteria lives freely in the soil and fixes nitrogen.
It is always suggested that not to eat anything from street hawkers. Why?
Most of street hawkers sells food items in an open area which always get contaminated with the dust and flies carrying germs with them. Such an unhygienic condition lead to spoilage of food which when consumed can lead to serious illness.
Why oil is added while making pickle?
Oil seals off the air from the item that is being pickled and thus inhibit the growth of most of the microorganisms.
Ria thought of making curd. For this, she took lukewarm milk, mixed some curd into it and stir well. She kept the mixture in fridge. Next day she observed that curd was not set. Can you tell why the curd did not set?
Curd did not set because she kept the mixture in fridge. Lower temperature of fridge retarded the growth of Lactobacillus in the mixture.
Why do idli and dosa maker add some yeast or old batter of pervious day to the newly-made batter and keep it for one day?
For fermentation of idli and dosa yeast or old batter is added. Fermentation makes idli fluffy and dosa crispy, and change the flavour.
Microorganisms: Friend and Foe Class 8 Extra Questions Value-Based Questions
Seema got cough and cold badly. Her teacher asked her to take rest at home and use handkerchief while sneezing and coughing. She obeyed her teacher.
(a) Why should we keep a handkerchief on nose and mouth while sneezing or coughing?
(b) What are the modes of transfer of diseases from infected to healthy person?
(c) Do you think Seema’s teacher decision was right? Why?
(d) What value of Seema is shown here?
(a) We should keep a handkerchief on nose and mouth while sneezing or coughing because fine drop¬lets carrying thousands of viruses or bacteria spread in the air.
(b) Air, water, food, carriers and physical contact.
(c) Yes, because cough and cold spreads through air and there are chances that other students may also get infected.
(d) Seema is an obedient girl.
On Rahul’s birthday, his mother prepared many dishes for him. After having their meal, they found that many food items were left over. Rahul’s mother kept these leftovers in a air-tight container and refrigerate them.
(a) What is food preservation?
(b) What will happen to the food if it is not refrigerated?
(c) What is the role of refrigeration in food preservation method?
(d) What value of Rahul’s mother is shown here?
(a) The methods used for prevention of spoiling of food by the action of microbes is called food preservation.
(b) The food will get spoil and emit bad smell with changed colour or taste.
(c) Refrigeration retards or slow down the growth of microorganisms and enzyme activity on food. Thus, it prevents spoilage of food.
(d) Rahul’s mother is intelligent, economical, have scientific aptitude towards preservation of food.
Activities and Projects
Pull out a gram or bean plant from the field. Observe its roots. You will find round struc¬tures called root nodules on the roots. Draw a diagram of the root and show the root nod¬ules.
Collect the labels from the bottles of jams and jellie on the labels.
Do it yourself.
Visit a dcotor. Find out why antibiotics should not be overused. Prepare a short report.
To kill or stop the development of the disease-causing microbes, antibiotics are the medicines which are majorly used.
It’s very important to keep in mind that antibiotics must be taken only on the advice of a qualified doctor. Also, one should finish the prescribed course of antibiotics given by the doctor. If one takes an an¬tibiotic when not required or overuse it, then it will help bacteria in one’s body to develop resistance to the given antibiotic. Next time when one falls sick and needs that antibiotic, it will be less effective. Excess dose of antibiotics also kills friendly microbes inside our body and thus helps to flourish patho-genic microbes.
Project: Requirements 2 test tubes, marker pen, sugar, yeast powder, 2 balloons and lime water.
Take two test tubes and mark them A and B. Clamp these tubes in a stand and fill them with water leaving some space at the top. Put two spoonfuls of sugar in each of the test tubes. Add a spoonful of yeast in test tube B, Inflate the two balloons incompletely. Now tie the balloons on the mouths of each test tube. Keep them in a warm place, away from sunlight. Watch the setup every day for next 3-4 days. Record your observations and think of an explanation.
Now take another test tube filled 1/4 with lime water. Remove the balloon from test tube B in such a manner that gas inside the balloon does not escape. Fit the balloon on the test tube and shake well. Observe and explain.
It was observed that the balloon fitted on test tube B is completely inflated but balloon fitted on test tube A is not inflated. When the inflated balloon of test tube B is fitted on test tube filled with lime water, lime water turns milky. This is because yeast celj releases C02 during respiration which inflates the balloon and C02 present inside the balloon changes lime water milky.
I. Multiple Choice Questions (MCQs)
Choose the correct option.
Tiny organisms which cannot be seen with the naked eyes are called
Microorganisms are also known as
Fungus can be seen with a
(c) magnifying glass
(d) both (a) and (c)
Microorganisms that causes disease are also kn
Pathogens are also called
Bacteria are organisms.
Bacilli are the bacteria that are
Spherical-shaped bacteria are called
Simple, plant-like microorganisms are called
(c) both (a) and (b)
Medium that transmits pathogens from an infected person to a healthy one is called
(d) none of these
Medicine that kills or stops the growth of harmful disease-causing microbes is known as
The process in which sugar in the food is transformed into alcohol and carbon dioxide by using microorganisms is known as
The fungus that is commonly used in bakery and beverage industries is
Giardia is listed under the category of
Substance used to produce immunity against diseases in the living body is called
II. Fill in the Blanks
Fill in the blanks with suitable word/s.
1. Bacteria, fungi, protozoa and _______ are the major four groups in which microorganisms are classified.
2. Two microorganisms which live in symbiotic association in lichens are _______ and _______.
3. We use a _______ to see the microorganisms.
4. _______ are considered different from other microorganisms because they can multiply only by entering the host organisms.
5. The gas released during the preparation of bread is _______.
6. The disease caused by a protozoan and spread by an insect is _______.
7. _______ are curved-shaped bacteria.
8. Saprophytes and _______ are the two main categories of fungi.
9. _______ are the threads of the multicellular fungi.
10. Yeast is a _______ fungus.
11. Protozoa are _______ in nature.
12. Flu, cough and cold are caused by _______.
13. The first antibiotic discovered was _______.
14. _______ are the microorganisms that help in the process of decomposition.
15. The process of formation of curd from milk is known as the _______ of milk.
2. algae, fungus
5. carbon dioxide
III. Match the following
Match the items given in column I suitably with those given in column II.
IV. True or False
State whether the given statements are true or false.
1. Microbiology is the science of study of microbes.
2. All the microorganisms are harmful.
3. An instrument called microscope is required to see the microorganisms.
4. Bacteria have an organised nucleus.
5. Microorganisms are found in large number around us.
6. Viruses are the most useful microbes.
7. Anabaena is listed in the category of algae.
8. Algae tend to develop on wet surfaces.
9. Amoebic dysentery is caused by algae.
10. A fungi is used in the production of alcohol.
11. Jellies, jams and squashes are preserved by adding vinegar to them.
12. Salt is used as a food preservative.
13. Oxygen alone constitutes 78% of air.