Important Terms On Class 8 Science Chapter 2
1. Microorganisms
This part of chapter 2 of Class 8 Science focuses a branch of microbiology which introduced the importance of microorganism in our ecosystem. We have seen several kinds of plants and animals. However, there are many living organisms around us which we cannot see with eyes alone. These are called microorganisms or microbes, such as bacteria, fungi, protozoa and some algae. For example, you might have observed that during rainy season moist bread gets to spoil and its surface gets covered with greyish-white patches.
2. Microorganisms And Diseases
Remember, water and soil are full of tiny organisms, but all of them not comes into microorganisms or microbe’s category. Do you know? Viruses are also microorganisms. They reproduce only inside the cells of the host organisms and cause serious disease like Polio, Chickenpox, Common cold. Diseases like Typhoid, Tuberculosis are bacterial diseases which are caused by protozoans.
3. Where Do Microorganisms Live?
Microorganisms can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found in polluted air and water as well as in inside the bodies of animals, including humans. Remember, microorganisms like amoeba can live alone while fungi and bacteria may live in colonies.
4. Microorganisms And Us
In this part of the content discusses the role of microorganisms, if microorganisms are good or bad for us. Thus, this part of the chapter will help, to an extent, in clearing this matter. As you know, that microorganisms play an essential role in our lives. Some of them are beneficial in many ways, whereas some others are harmful and causes diseases. They are used for various friendly purposes as they are used in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals, faeces etc.) are broken down into harmless and usable substance by bacteria, called manure. In agriculture, they are used to increase soil fertility by fixing nitrogen.
5. Microorganisms As A Friends
You may know that microorganisms are used for the preparation of curd, bread and cake. Curd contains several microorganisms. The bacterium Lactobacillus promotes the formation of curd. Similarly, yeast is also used in the baking industry for making slices of bread, pastries and cakes. Microorganisms are also used for the large-scale production of alcohol, wine and acetic acid. As yeast is used for the smell of alcohol as sugar converts into alcohol. The process of conversion of sugar into alcohol is called ‘fermentation’.
6. Microorganisms In Medicine
Whenever we fall ill, the doctor gives us some antibiotic tablets, capsule or injection. The sources of these medicines are microorganisms. Do you think why they are used? These medicines kill or stop the growth of the disease-causing microorganisms. Hence, such medicines are called ‘Antibiotics’. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases. When a disease-carrying microbe enters our body, the body produces ‘antibodies’ to fight the invader. In our childhood, we must have been given an injection for ‘Smallpox’ and ‘Polio’ to protect our-self against these diseases. Generally, these vaccines are made from microbes or microorganisms.
7. Microorganisms As Decomposer
As you learn before, some bacteria and blue-green algae are able to fix nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility. You often see a large amount of dead organic matter in the form of decaying plants and dead animals on the ground. You find that they disappear after some time. This is because the microorganisms decompose dead organic waste of plants and animals, converting them into manure or nutrients. The other plants and animals again use these substances.
8. Harmful Microorganisms
This part of the Class 8 Science deals with some diseases which are caused by microorganisms. Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals, called ‘Pathogens’.
9. Disease – Causing Microorganisms In Humans
Microbial diseases that can spread from an infected person to a healthy person through the air, water, food or physical contact, called ‘Communicable Diseases’. When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air, and then through the air, the virus enters the body of a healthy person while breathing. There are some insects and animals which act as ‘carriers’ of diseases causing microbes. Such as houseflies, mosquitoes, cockroach etc. Remember, ‘Anopheles Mosquito’ which careers the parasite of malaria. ‘Female Aedes’ mosquito act as a carrier of the dengue virus.
10. Disease – Causing Microorganisms In Animals And Plants
Anthrax is a dangerous human and cattle disease caused by the bacterium. Several microorganisms are there which causes diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. These diseases reduce the yield of crops. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous, causing severe illness and even death.
11. Food Preservation
In this part of the content gives an idea about food preservation from microorganism or microbes. As you know, spoilt food emits a bad smell and has a bad taste and change colour. So, it is very important that we preserve food to prevent it from being spoilt. Salt and edible oils are common chemicals generally used to check the growth of microorganisms, called ‘Preservatives’. Common salt has been used to preserve meat and fish for ages. Jams, jellies and squashes are preserved by sugar. As you know, boiling kills many microorganisms. You must have noticed that your mother is boiling milk before it is stored or used. Now in a day, dry fruits and even vegetables are sold in sealed airtight packets to prevent the attack of microbes.
12. Nitrogen Cycle
We know that our atmosphere has 78% nitrogen gas. Light and Nitrogen are the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acid and vitamins. Nitrogen cannot be taken by plants and animals directly. Certain bacteria and blue-green algae fix the nitrogen from the atmosphere and convert into compounds of nitrogen in the soil. When plants and animals die, bacteria and fungi convert the nitrogenous waste into nitrogenous compounds. And again, used by plants. As a result, the percentage of nitrogen in the atmosphere remains constant.
13. Nitrogen Fixation
As you know, the involvement of rhizobium bacteria in the fixation of nitrogen for leguminous plants. Rhizobium lives in the root nodules of leguminous plants and converts nitrogen into a soluble form for them. But that bacteria cannot make their own food. In return, leguminous plants provide food and shelter to the rhizobium bacteria. In this way, you can see microorganisms have tons of benefits, and they can cause deadly diseases too. As they are crucial in maintaining a balance in our ecological system, which helps to survive all living organisms.
Class 8 Science Chapter 2 Important Questions For Practice
Can Microorganisms Be Seen With The Naked Eye? If Not, How Can They Be Seen?
No, microorganisms cannot be seen by naked eye as they are very small and are called microbes. They can be seen with the help of microscope.
What Are The Major Groups Of Microorganisms?
Microorganisms are classified into four major groups are bacteria, fungi, protozoa and some algae.
Name The Microorganisms Which Can Fix Atmospheric Nitrogen In The Soil.
Bacteria such as rhizobium and certain blue-green algae present in the soil can fix atmospheric nitrogen and convert into usable nitrogenous compounds, which are used by plants for the synthesis of plant proteins and other compounds.
What Are Antibiotics? What Precautions Must Be Taken While Taking Antibiotics?
The medicines that kill or stop the growth of the disease – causing microorganisms are called antibiotics.
For example: Streptomycin, tetracycline, etc.
Following precautions must be taken while taking antibiotics:
Antibiotics should be taken only on the advice of a qualified doctor.
One must finish the course prescribed by the doctor.
Antibiotics must be avoided when not needed or in wrong doses.
Class 8 Science Chapter 2 MCQ With Answers
1. Which of the following reproduces only inside a host cell?
(a) Bacteria
(b) Virus
(c) Amoeba
(d) Fungus.
2. Paheli dug two pits, A and B, in her garden. In pit A, she put a polythene bag packed with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month?
(a) Waste in pit A degraded faster than that in pit B.
(b) Waste in pit B degraded faster than that in pit A.
(c) Waste in both pits degraded almost equally.
(d) Waste in both pits did not degrade at all.
3. A disease in human beings caused by virus is _______.
(a) typhoid
(b) influenza
(c) dysentry
(d) cholera
4. The two micro-organisms which live in symbiotic association in lichens are
(a) fungus and protozoa
(b) alga and bacteria
(c) bacteria and protozoa
(d) alga and fungus
5. The disease caused by a protozoan and spread by an insect is _________.
(a) dengue
(b) malaria
(c) polio
(d) measles
6. The gas released during the preparation of bread is
(a) oxygen
(b) carbon dioxide
(c) nitrogen
(d) sulphur dioxide
7. Pathogenic micro-organisms present in host cells are killed by medicines called
(a) pain killer
(b) antibodies
(c) antibiotics
(d) vaccines
8. Unscramble the jumbled words underlined in the following statements.
(a) Cells of our body produce santiidobe to fight pathogens.
(b) curbossulite is an air-borne disease caused by a bacterium.
(c) Xanrhat is a dangerous bacterial disease.
(d) Yeasts are used in the wine industry because of their property of meronettinaf.
Answers Of Important Questions
1 (b)
2 (b)
3 (b)
4 (d)
5 (b)
6 (b)
7 (c)
8 (a) antibodies (b) tuberculosis (c) Anthra (d) fermentation
Class 8 Science Chapter 2 Important Questions Set – 1
Where Do Microorganisms Live? Discuss.
Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular, such as algae and fungi. They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
How Does Microorganisms Increase The Soil Fertility?
Microorganisms play an important role in our lives. Microorganisms are used for various purposes. For example, the organic wastes (vegetable peels, remains of animals, faeces, etc.) are broken down into harmless and usable substances by bacteria. Bacteria are also used in the preparation of medicines. In agriculture they are used to increase soil fertility by fixing nitrogen.
Which Bacteria Is Responsible For Making Curd?
Curd contains several micro-organisms. Of these, the bacterium “Lactobacillus” promotes the formation of curd. It multiplies in milk and converts it into curd.
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With The Help Of An Activity, Say How Yeast Is Used For Baking Industry?
Take 1⁄2 kg flour (atta or maida), add some sugar and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough. We find after two hours that the dough is rising. Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume.
This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
Microbes Or Microorganisms
There are some living organisms around us which we cannot see with eyes alone. These microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Therefore, these are known as microorganisms or microbes. Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.
Class 8 Science Chapter 2 Important Questions Set – 2
With The Help Of Activity, Which Condition Is Known As “Fermentation”?
Microorganisms are used for the large-scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine.
Take a 500 mL beaker filled up-to 3⁄4 with water. Dissolve 2-3 teaspoons of sugar in it. Add half a spoon of yeast powder to the sugar solution. Keep it covered in a warm place for 4-5 hours. Then solution gives a smell.
This is the smell of alcohol as sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.
Name Any Two Antibiotic Medicine Which Are Made From Fungi And Bacteria.
Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotic medicines which are made from fungi and bacteria.
Discuss, How Does A Vaccine Work In Our Body?
When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease- causing microbes. This is how a vaccine work in our body.
Name Any Three Viruses Caused Diseases Which Are Eradicated From Most Parts Of The World.
COVID-19, Smallpox and Polio are led to its eradication from most parts of the world.
The Role Of Antibiotics
Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.
These days a number of antibiotics are being produced from bacteria and fungi. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases.
Class 8 Science Chapter 2 Important Questions Set – 3
Boojho And Paheli Are Surprised To Know That How Do Waste Of Plant, Vegetable And Fruits Converted Into Manure? Will You Help Them To Understand?
The plant waste has been converted into manure by the action of microbes. The nutrients released in the process could be used by the plants again.
We often see large amounts of dead organic matter in the form of decaying plants and sometimes dead animals on the ground. We find that they disappear after some time. This is because the microorganisms decompose dead organic waste of plants and animals converting them into simple substances. These substances are again used by other plants and animals.
Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.
We Should Keep A Handkerchief On The Nose And Mouth While Sneezing”. Why?
When a person suffering from common cold and sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing. That’s why, we should keep a handkerchief on the nose and mouth while sneezing
It Is Advisable To Always Keep Food Covered”. Why?
There are some insects and animals which act as carriers of disease- causing microbes. Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food, they may transfer the pathogens.
Whoever eats the contaminated food is likely to get sick. So, it is advisable to always keep food covered. Avoid consuming uncovered items of food.
Which Mosquitoes Are Known As Carrier Of Dengue Virus And Carrier Of Parasite Of Malaria?
“Female Aedes” mosquito acts as carrier of dengue virus. Another example of a carrier is the “female Anopheles” mosquito, which carries the parasite of malaria.
Communicable Disease
Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.
Generally, pathogens spread as they enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal.
Class 8 Science Chapter 2 Important Questions Set – 4
How Can You Control The Spread Of Malaria And Dengue? Suggest Any Two Ways.
All mosquitoes breed in water. First, we should not let water collect anywhere, in coolers, tyres, flower pot etc. Second, by keeping the surroundings clean and dry we can prevent mosquitoes from breeding.
Write Down The Preventive Measures Of Cholera And Typhoid Which Are Caused Due To Bacteria.
The transmission of bacteria caused cholera and typhoid diseases due to contaminated food and water. Therefore, general preventive measures are maintaining personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. And take consult with doctor.
What Do You Mean By “Preservatives”? Write Down The Two Ways Of Food Preservative.
We know that bread left unused under moist conditions is attacked by fungus. Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and changed colour.
A preservative is a substance or a chemical that is added to products such as food products, beverages, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by undesirable chemical changes.
Therefore, salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore, they are called preservatives.
The two ways of food preservative are:
i)Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria.
ii)Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment.
Why Should We Avoid Standing Close To The Tuberculosis Patient While He Or She Is Coughing?
Tuberculosis is an airborne disease which is easily spreads when the infected person cough. As coughing is spreads germs in the air and these germs remain suspended in air until inhaled by person present in proximity of the patient who is suffering from the disease. That is why we should avoid standing close to a TB patient.
Pasteurization
Boiling kills many microorganisms. Low temperature inhibits the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 70 degree Celsius for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes.
This process was discovered by “Louis Pasteur”. Therefore, it is called pasteurization.
Class 8 Science Chapter 2 Important Questions Set – 5
Write “Five To Six” Lines On The Usefulness Of Microorganisms In Our Lives.
Microorganisms are too small to be seen through naked eyes. However, they are vital to plants and the environment.
Importance of microorganisms:
1)They are used in wine making, baking, pickling and other food making processes.
2)Alcoholic fermentation by yeast is widely used in the preparation of wine and bread.
3) A bacterium lactobacillus promotes the formation of curd.
4) They are used to increase the soil fertility by fixing the atmospheric nitrogen.
5) Microbes are also useful in preparing many medicines and antibiotics.
6) Certain microbes are also used in the biological treatment of sewage and Industrial effluents.
How Do Vaccines Work?
Vaccines contain dead for weakened microbial strains of a particular disease. When a vaccine is introduced into a healthy body. It produces specific cells against the pathogen. These cells are called antibodies and they become active when the pathogen affect our body. The body fights and kills them by producing specific set of reactions. These antibodies remain in the body for life long and protect against the microbe when microbe enters the body again. Vaccines can be given either orally (in the forms of drops) or injected in the body.
Write A Short Paragraph On The Harms Caused By Microorganisms?
Microorganisms are harmful in many ways. Some of the microorganisms are diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather. Some of the common disease is affecting humans are common cold, chicken pox and tuberculosis. Several micro-organisms not only cause diseases in humans but also in animals.
For example, “Anthrax” is a dangerous human and cattle disease is caused by a bacterium. Disease causing microorganisms in plants like wheat, rice, potato, sugarcane, orange, apple and others reduce the yield of crops
While Returning From A School, Boojho Ate Chaat From A Street Hawker. When He Reached Home, He Felt Ill And Complained Of Stomach Ache And Feel Ill. What Could Be The Reason?
The reason could be that the chaat was contaminated by pathogenic microorganisms. The unhygienic conditions present near the shop becomes the breeding place for microbes, flies etc. The pathogens can be transmitted to places by flies and other vectors, even the utensil used for serving could have been contaminated by the pathogenic microorganism. If such microbial contaminated food is consumed several diseases like diarrhoea, dysentery, cholera etc. may occur.
Nitrogen Cycle
Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.
Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds.
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.