1. Microorganisms-
ü Organisms which are too small to be seen by the naked eye, mainly the single celled organism is called microorganisms or microbes.
ü Microorganisms are classified into four major groups- bacteria, fungi, protozoa and some algae.
ü Microorganisms may be single celled - bacteria, some algae and protozoa or multi-cellular algae and fungi that can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.
ü They are also found inside the bodies of other organisms including humans.
ü Growth of some microorganisms depends on other organisms while other organisms exist freely.
ü Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
ü Viruses are also microscopic. They reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
ü Virus can not multiply in medium free of life.
Figure 01- Bacteria
Figure 02- Algae and protozoa
Figure 03- Fungi Figure 04- Virus
2. Friendly Microorganisms And Their Role In Our Life-
ü In agriculture fields, microorganisms are used to increase soil fertility by fixing nitrogen.
ü Some microorganisms are used in the preparation of curd, bread and cake.
ü Some microorganisms have been used for the preparation of alcohol since ages.
ü They are also used in cleaning up of the environment as decomposers.
ü Commercial Use of Microorganisms-
n For large scale production of alcohol, wine and acetic acid, microorganisms are used.
ü Medicinal Use of Microorganisms-
n These days the medicines produced from Bactria and fungi kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.
n Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections like peenicillin which are made up of microorganism.
n Streptomycin, tetracycline and erythromycin medicines which are made from fungi and bacteria are some of the commonly known antibiotics.
n The antibiotics are made by growing specific microorganisms and are used to cure a variety of diseases.
n Antibiotics are even added with the feed of livestock and poultry for checking microbial infection in animals.
ü Nowadays microorganisms are also used to control many plant diseases.
ü Increasing Soil Fertility-
Figure 05- Nitrogen fixing cyno bacteria (blue-green algae)
n Some bacteria and blue green algae are able increase the fertility of soil by fix nitrogen from the atmosphere to enrich soil with nitrogen. These microbes are commonly called biological nitrogen fixers.
ü Cleaning the Environment-
n At the time of making manure, we collect wastes of plants, vegetables and fruits. Then we put them in a pit meant for waste disposal. After some time, it decomposed by microorganisms and gets converted to manure. By this method environment is cleaned by microorganisms.
2. Disease Causing Microorganisms In Humans-
ü Disease causing microorganisms are called as pathogens.
ü Pathogens enter our body through the different way like air when we breathe, the water when we drink or the food when we eat.
ü They can also get transmitted by direct contact with an infected person or carried through an animal.
ü Examples of microbial diseases include cholera, common cold, chicken pox and tuberculosis that can spread from an infected person to a healthy person through air, water, food or physical contact.
ü Such spreadable diseases are called communicable diseases.
ü There are some insects and animals which act as carriers of disease causing microbes.
ü For example housefly is one such carrier that flies sit on the garbage and animal excreta etc. Pathogens stick to their bodies. When these flies sit on uncovered food they transfer the pathogens. Whoever eats the contaminated food is likely to get sick. Some more examples of carrier microbes are the female Anopheles mosquito, which carries the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus.
ü Mosquitoes breed in water. So, one should not let water collect anywhere like in coolers, tyres, flower pot etc. By keeping the surroundings clean and dry we can prevent mosquitoes from breeding.
ü Disease Causing Microorganisms In Animals-
n Some of microorganisms not only cause diseases in humans and plants, but also in other animals. For example: anthrax is an example of dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.
Table O1- Microbes and diseases (Animals)
ü Disease Causing Microorganisms In Plants-
n Some of microorganisms cause diseases in plants such as wheat, rice, potato, sugarcane, orange, apple and others. These diseases reduce the yield of crops. They can be controlled by the use of certain chemicals or pesticides which kill the microbes, which affect the yield the crops.
Table O2- Microbes and diseases (Plants)
4. Vaccine-
ü When a disease-carrying microbe enters our body, the antibodies produced by our body fight with the invader.
ü If microbes enter again, the body also remembers that how to fight with the microbes.
ü If dead or weakened microbes are injected in a healthy body, the body fights and kills them by producing suitable antibodies.
ü The antibodies remain in the body for protecting from the disease causing microbes.
ü This is how a vaccine works.
ü Several diseases like cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
5. Food Poisoning-
ü Food poisoning in humans could be due to the consumption spoiled food by some microorganisms.
ü Microorganisms that grow on our food produce toxic substances and make the food poisonous causing serious diseases.
ü It is very important that we preserve food to prevent it from being spoilt by the microorganisms.
ü Food Preservation-
n Microorganisms spoil our food.
n Spoiled food gives bad smell and has a bad taste and changed colour.
6. Food Preservation-
ü Chemical Method-
n Preservatives like Salts and edible oils are the common chemicals generally used to check the growth of microorganisms.
n We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium meta bisulphite are common preservatives which are used in the jams and squashes to check their spoilage.
ü Preservation By Using Common Salt-
n To preserve meat and fish for ages, common salt is used. Meat and fish are covered with dry salt to check the growth of bacteria.
n Salting is also used to preserve amla, raw mangoes, tamarind, etc.
ü Preservation By Using Sugar-
n Sugar is used for preserving jams, jellies and squashes are preserved.
n It reduces the moisture content which inhibits the growth of bacteria which spoil food.
ü Preservation By Oil And Vinegar-
n Oil and vinegar are used to prevent spoilage of pickles because bacteria cannot live in such an environment.
n Vegetables, fruits, fish and meat are often preserved by this method.
ü Heat And Cold Treatment-
n Boiling of milk kills many microorganisms, after that it is stored or used.
n We keep our food in the refrigerator. Low temperature inhibits the growth of microbes.
n Pasteurized milk can be taken without boiling as it is free from harmful microbes. The milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, this process prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.
ü Storage And Packing-
n Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.
7. Nitrogen Fixation-
ü Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins, available 78% in our environment.
ü Bacteria and blue green algae present in the soil for fixing nitrogen from the atmosphere and then convert into compounds of nitrogen.
ü Rhizobium is involved in the fixation of nitrogen in leguminous plants.
ü Nitrogen also gets fixed through the action of lightning. But the amount of nitrogen remains constant in the atmosphere.
ü After this, usable compounds can be utilized by plants from the soil through their root system. These compounds are then used for the synthesis of plant proteins and other compounds.
ü Animals feeding on plants get these proteins and other nitrogen compounds.
ü 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.
ü Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere.
ü As a result, the percentage of nitrogen in the atmosphere remains more or less constant.
Cycle O1- Nitrogen Cycle
NCERT PRACTICE QUESTIONS
1. Fill in the blanks.
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue green algae fix __________ directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.
Ans.- a) Microscope b) Nitrogen c) Yeast d) Bacteria- Vibrio cholera
2. Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen
(b) The following is an antibiotic
(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly
(d) The most common carrier of communicable diseases is
(i) ant (ii) housefly (iii) dragonfly (iv) spider
(e) The bread or idli dough rises because of
(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection
Ans.- a) (ii) alcohol b) (ii) Streptomycin c) (i) female Anopheles mosquito d) (ii) housefly e) (iii) growth of yeast cells f) (iii) fermentation
3. Match the organisms in Column A with their action in Column B.
Ans.-
A | B |
(i) Bacteria | (e) Causing cholera |
(ii) Rhizobium | (a) Fixing nitrogen |
(iii) Lactobacillus | (b) Setting of curd |
(iv) Yeast | (c) Baking of bread |
(v) A protozoan | (d) Causing malaria |
(vi) A virus | (f) Causing AIDS |
4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Ans.- Microorganisms cannot be seen by the naked eye because they are very small. They can be seen by using a microscope.
5. What are the major groups of microorganisms?
Ans.- Major group of microorganisms are - Bacteria, Fungi, Protozoans, Algae and Viruses.
6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Ans.- Rhizobium
7. Write 10 lines on the usefulness of microorganisms in our lives.
ü Microorganisms decompose dead organic waste of plants and animals to convert 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.
ü They are helpful 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 substances by bacteria.
ü 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.
ü Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
ü Bacteria are also involved in the making of cheese, pickles and many other food items.
ü Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
ü Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).
ü Antibiotics are being produced from bacteria and fungi.
ü Microorganisms are helpful in producing vaccines against disease-causing agents.
ü Some bacteria are able to fix nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility.
8. Write a short paragraph on the harmful effects of microorganisms.
Ans.- Microorganisms cause diseases in plants and animals Ex; Cholera in humans is caused by bacteria called Vibrio cholera. In animals, the virus causes foot and mouth diseases. Microorganisms spoil the foods by decomposing the food material. Some microorganisms spoil leather and clothes. Microorganisms are responsible for food poisoning.
9. What are antibiotics? What precautions must be taken while taking antibiotics?
Ans.- Chemical agents that kill or stop the growth of disease-causing microorganisms are called antibiotics. Antibiotics should be taken only on the advice of a qualified doctor. Also, one must complete the course prescribed by the doctor.
Junior Science Topic - Microorganisms- Friends Or Foe. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 8, CBSE syllabus, chapter 02)
By - EduPorm India - The Educational Platform
.png)
){kind=link}