Microorganisms Friend and Foe Notes || Class 8 Chapter 2 Science ||
Chapter – 2,
Science
MICROORGANISMS:
FRIEND AND FOE
1. Microorganisms/microbes are very small which cannot be seen with
the help of eyes.
2. We use microscope or magnifying glass to see them.
3. E.g. fungus that grows on bread
Classification of Microorganisms
1. It is
classified into four major groups
2. Bacteria, fungi, protozoa and algae
3. Viruses are other kind of
microorganisms.
4. They are explained below –
Bacteria
1.
Bacteria are very
small, single celled micro-organisms which have cell walls but do not have an
organised nucleus & other structure
2. These are found everywhere like in air, soil, water, every
surface around us, on our bodies or inside our body.
3. Two common examples are Lactobacillus & Rhizobium
4.
Some are useful
& help in making foods (like curd (दही)) & some can cause disease like cholera (हैजा), typhoid (मियादी बुखार), tuberculosis (TB) & food Poisoning (पेट दर्द).
Protozoa
1.
It is a single celled
micro-organism.
3. Some common examples of protozoa are Amoeba, paramecium,
Plasmodium.
Algae
1.
It is a large group
of simple, plant like organisms.
2. They contain chlorophyll & produce food by photosynthesis
just like plants.
4.
Some are
unicellular & most of the algae are multicellular.
Fungi
1.
Fungi are a large
group of organisms which do not have chlorophyll & photosynthesis.
2. Some examples are Yeast, Moulds (such as bread mould,
penicillium), Mushrooms etc.
3. Some fungi look like plants but they cannot make their own food
like the plants.
4. They food on dead things like remains of dead plants &
animals
5.
Fungi need moist
& warm conditions to grow.
Viruses
1.
Viruses are the
smallest micro-organisms which can develop only inside the cells of the host
organisms (may be animals, plants)
2. Viruses can reproduce & multiply only inside the cells of
other organisms (such as animal cell, plant cell or organisms cell)
3. Thus, as long as viruses are outside the living cells, they
behave as non-living things.
4.
Diseases produced
by them are common cold, influenza (ज़ुकाम) (flu), measles (खसरा), polio, chickenpox & smallpox etc
Where do Microorganisms Live?
1.
Microorganisms may
be single-celled like bacteria, some algae and protozoa, or multicellular, such
as many algae and fungi.
2. They can live from cold to hot climate.
3.
They are found
everywhere in all types of habitats like air, soil, water bodies, inside the
bodies of animals including humans or depend on other organisms.
Microorganisms and Us
Some microorganisms are beneficial & some others are harmful and cause diseases.
Friendly Microorganisms
1.
Microorganisms are
used for various purposes.
2. They are used in the preparation of curd, bread, cake & alcohol.
Making of Curd
1.
Curd contains
several microorganisms.
2. Of these, the Lactobacillus bacterium is multiplies
itself & converts milk into curd.
3.
Bacteria are also
involved in the making of cheese (पनीर), pickles (अचार) and many other food items.
Commercial Use of Microorganisms
1.
Microorganisms are
used for the large scale production of alcohol, wine and acetic acid (vinegar [सिरका]).
3. Sugar has been converted into alcohol by the use of yeast.
4. This process of conversion of sugar into alcohol is known as fermentation.
5. Note – Louis
Pasteur discovered fermentation in 1857.
Medicinal Use of Microorganisms
1.
Whenever we fall
ill the doctor may give us some antibiotic tablets or injections such as of
penicillin.
2. These medicines kill or stop the growth of the disease-causing
microorganisms.
3. Such medicines are called antibiotics.
4. Many antibiotics are being produced from bacteria and fungi.
5.
E.g. Streptomycin,
tetracycline and erythromycin
Important to Note
1.
In 1929, Alexander
Fleming was working on a culture of disease causing bacteria.
2. Suddenly he found the spores (जीवाणु जो बढ़कर एक नया प्राणी हो जाता है) of a little green mould in one of his culture plates.
3. He observed that the presence of mould prevented the growth of
bacteria.
4.
In fact, it also
killed many of these bacteria. From this the mould penicillin was prepared.
Preventions in the Use of Antibiotics
1. Antibiotics should be taken only on
the advice of a qualified doctor.
3.
If
you take antibiotics when not needed or in wrong doses, it may make the drug
less effective when you might need it in future.
4.
Also
antibiotics taken unnecessarily may kill the beneficial bacteria in the body.
5. Antibiotics are not effective
against cold and flu as these are caused by viruses.
Vaccine
1.
A vaccine is a
special kind of medicine which provides immunity (मुक्ति) or protection against a particular disease.
2. Vaccination is a process of giving a vaccine orally (by mouth)
or by injection which provides protection against a particular disease like
polio, Tetanus, Measles, Rabies cholera, tuberculosis (TB), smallpox and
hepatitis.
3. Edward Jenner discovered the vaccine for
smallpox in 1798.
Increasing Soil Fertility
1.
Some of the
micro-organisms present in the soil can fix nitrogen gas from the atmosphere to
form nitrogen compounds.
3. E.g. some bacteria like Rhizobium & blue green algae are
able to fix nitrogen gas from atmosphere to enrich the soil with nitrogen
compounds & increase its fertility.
4.
These bacteria
& blue green algae are commonly called biological nitrogen fixers.
Cleaning the Environment
1.
Some
micro-organisms (Like some bacteria & fungi) decompose (सड़ जाना) the harmful and smelly dead remains of plants and animals, and animal
wastes (like faeces [मल], dung [गोबर], and urine) into harmless materials which mix up with soil.
2. These harmless materials or simpler substances contain plant
nutrients which are used by the new plants for their growth.
3.
In this way, it
cleans the environment.
Harmful Microorganisms
2. Such disease-causing microorganisms are
called pathogens.
3. Pathogens can be bacteria, viruses,
protozoa, or fungi etc.
4. Microorganisms cause disease such as
cholera (हैजा), common cold, chicken pox, tuberculosis
(TB), tetanus, food poisoning etc.
Disease causing Microorganisms
in Humans
1.
Pathogens
enter our body through the air we breathe, the water we drink or the food we
eat.
2. They can also get transmitted by direct
contact with an infected person or carried by an animal.
3. Microbial diseases that can spread from an
infected person to a healthy person through air, water, food or physical
contact are called communicable diseases.
4. Examples cholera, common cold, chicken pox
and tuberculosis.
5. When a person suffering from common cold
sneezes (छींकना), fine droplets of moisture carrying thousands of viruses are spread
in the air.
6.
The
virus may enter the body of a healthy person while breathing and cause
infection.
Prevention of communicable
diseases
1.
A
person suffering from common cold should always cover his mouth and nose with a
handkerchief while sneezing.
3. We should protect ourselves from mosquito
bites by using mosquito nets over our beds.
4.
We
should avoid physical contact with an infected person & not use his towel,
clothes.
Carriers of Disease-causing
Micro-Organisms
1.
There
are some insects and animals which act as carriers of disease-causing microbes.
2.
The
two most common insects – housefly & mosquito
Role of Housefly in spreading
diseases
1.
The houseflies
feed on garbage (कूडा), animal excreta (मल-मूत्र), dead organic matter and uncovered human
food.
2. The body and legs of housefly have a lot of
fine hair.
3. When the flies sit on a garbage heap (ढेर) or refuse (kachra) area, then millions of Disease-causing
Micro-Organisms (like bacteria) transfer to other places like our uncovered
food.
4. Then, these bacteria or germs enter into our
body as we eat this uncovered food.
5.
Some of
the dangerous diseases spread by houseflies like cholera, Tuberculosis (TB),
Typhoid & Diarrhea.
Prevention of Diseases spread by houseflies
1.
We should
not leave household garbage (कूडा) here
& there and it should be put in the garbage bins (कूड़ादान) which is properly covered.
2. Food always is kept covered.
3. Avoid eating uncovered food.
5.
Some
diseases spread by houseflies can be prevented by vaccinations.
Role of Mosquitoes in spreading
diseases
1.
Mosquito
spread diseases from one person to another.
2. Note here that housefly carries the diseases-causing
microbes (जीवाणु) on the hair (outside its body) but the mosquito carries microbes
inside its body.
3. Mosquito breed (नस्ल बढाना) in stagnant (गतिहीन) water of ponds, dirty drains (नाली), pools, shallow (कम गहरा) lakes etc.
4. The most common disease spread is ‘malaria’
6. The malarial parasite (called plasmodium)
causes malaria diseases.
7. Another disease spread by mosquito is
‘dengue’ & is caused by virus.
8.
The
female Aedes mosquito acts as a carrier of dengue virus & spread the dengue
disease from person to person.
Some Common Human Diseases
caused by Microorganisms
|
Human
Disease
|
Causative
Microorganism
|
Mode
of Transmission
|
Preventive
Measures (General)
|
|
Tuberculosis
Measles (खसरा)
Chicken Pox (छोटी चेचक)
Polio
|
Bacteria
Virus
Virus
Virus
|
Air
Air
Air/Contact
Air/Water
|
Keep the
patient in complete isolation (एकांत). Keep the personal belongings of the patient away from those of the others. Vaccination to be given at suitable age.
|
|
Cholera
Typhoid
|
Bacteria
Bacteria
|
Water/Food
Water
|
Maintain personal hygiene
and good sanitary habits. Consume properly
cooked food and boiled
drinking water. Vaccination.
|
|
Hepatitis (जिगर में सूजन) A
|
Virus
|
Water
|
Drink boiled drinking water. Vaccination.
|
|
Malaria
|
Protozoa
|
Mosquito
|
Use mosquito
net and repellents
(दूर भगाने वाला). Spray insecticides and control breeding of
mosquitoes by not allowing water to collect
in the surroundings.
|
Disease causing Microorganisms
in Animals
1.
Anthrax
is a dangerous human and cattle disease caused by a bacterium.
2.
Foot
and mouth disease of cattle is caused by a virus.
Disease causing Microorganisms
in Plants
1.
Several
microorganisms cause diseases in plants like wheat, rice, potato, sugarcane,
orange, apple and others.
2. The diseases reduce the yield of crops.
3.
They
can be controlled by the use of certain chemicals which kill the microbes.
|
Plant
Diseases
|
Micro-
organism
|
Mode
of Transmission
|
|
Citrus
canker
|
Bacteria
|
Air
|
|
Rust of
wheat
|
Fungi
|
Air seed
|
|
Yellow vein
mosaic of bhindi (Okra)
|
Virus
|
Insect
|
Food Poisoning
1.
If
the food is not covered properly, stored properly or preserved properly, then
it gets spoiled (खराब हो जाना) by the
micro-organisms (like bacteria & fungi) on it.
3. The diseases caused due to the presence of
a large number of micro-organisms in the food are called food poisoning.
Preservation of Food
1.
The process in which the food materials are given a suitable
physical or chemical treatment to prevent (रोकना)
their spoilage (खराब होना) is called food preservation.
2.
There are different methods to preserve the food
Chemical Method
1.
Salts
and edible oils are the common chemicals generally used to check the growth of
microorganisms.
2. Therefore, they are called preservatives.
4. Sodium benzoate and sodium metabisulphite
are common preservatives.
Preservation by Common Salt
2. Meat and fish are covered with dry salt to
check the growth of bacteria.
Preservation by Sugar
2.
Sugar
reduces the moisture content which prevents (रोकना) the growth of bacteria which spoil food.
Preservation by Oil and Vinegar
1.
Use
of oil and vinegar (सिरका) prevents spoilage of pickles because bacteria cannot live in such an
environment.
2.
Vegetables,
fruits, fish and meat are often preserved by this method.
Heat and Cold Treatments
1.
Boiling
kills many microorganisms.
2. Similarly, we keep our food in the
refrigerator.
3.
Low
temperature prevents the growth of microbes.
Pasteurisation
1.
Pasteurised
milk can be consumed without boiling as it is free from harmful microbes.
2. The milk is heated to about 700C
for 15 to 30 seconds and then suddenly chilled (ठंडा) and stored.
3. By doing so, it prevents the growth of
microbes.
4.
This
process was discovered by Louis Pasteur & called pasteurisation.
Storage and Packing
Dry fruits and
even vegetables are sold in sealed air tight packets to prevent the attack of
microbes.
Nitrogen Fixation
1.
The process of converting nitrogen gas of atmosphere into
compounds of nitrogen (which is used by plants) is called nitrogen fixation.
2.
The nitrogen gas of atmosphere can be fixed (converted into
nitrogen compound) – by certain nitrogen-fixing bacteria present in the soil,
by Rhizobium bacteria present in the roots, by blue-green algae
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