Science class 8 ch-2 important notes// Ak learning// Ak Raj.

Ch-2

MICROORGANISM FRIEND OR FOE

NOTES:-

2.2 MICROORGANISM:-

Those living organisms around us which we normally cannot see.These living organisms are called microorganisms.

The water and soil are full of tiny organisms through no all of them fall into the category of microbes. These microbes or microorganisms are so small in size they cannot seen with unaided eye.

Microorganisms are classified into four major groups are as below:-

• Bacteria
• Fungi
• Protozoa
• Algae

• Virus:- Virus is also a microscopic organism but these are different from microorganisms.They behave like non-living when they are outside the host cell,reproduce only when they are inside the host cell.

• Bacteria:-

• Bacteria are one of the oldest life forms.
• They are unicellular i.e. they are made up of one cell
• They appear in a variety of shapes & sizes  (Spericals,elongated,spiral etc.)
• They inhabit soil,water,radioactive waste & the deep portion of the earth's crust. In fact,they also live in the plant /animals.
• They live in colonies.
• Some of them are autotrophic while others are heterotrophic.

• Fungi:-

• Fungi are multicellular i.e They are made up of multiple cells.
• They are heterotrophic.
• They live in colonies and prefer moist places to grow.
• they are immobile.
• Some common examples of fungi are. yeast,mushroom,molds.

• Protozoa:-

• They are mostly unicellular.
• Some of them are autotrophic while others are heterotrophic.
• They prefer moist and aquatic habits.
• They live singly,unlike bacteria & fungi.
• Some common examples of protozoa are. amoeba,paramecium, trypanosoma.

• Algae:-

• They are multicellular.
• They prefer mostly aquatic habitats.
• Some common examples of algae are. spirogyra,ulothrix,chlamydomonas.

2.2 WHERE DO MICROORGANISMS LIVE

• They can survive (live) all types of environments 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.
• Amoeba live alone while others live in colonies.

2.3MICROORGANISMS AND US

    Microorganisms play an important role in our lives.

• Some of them are beneficial(friendly microorganisms)
• some of them are harmful and cause disease.(harmful microorganism)

Friendly microorganisms:-

• Microorganisms are used for various purposes. They  are used in preparation of curd,bread and cakes
• They are also used in cleaning up the environment.
• They increase the soil fertility.
• They are used to make medicines.
• they convert the organic waste to harmless substances.

Making of curd and bread:-

• Curd contains several microorganisms. lactobacillus promotes the formation of curd.
• It multiplies in the milk and converts it into cord.
• Bacteria are also involved in making cheese, pickles and many other food items.
• An important ingredient of rava(sooji) idlis and bhaturas is curd.
• Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
• Yeast reproduce rapidly and produce carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is baisc use of yeast (microorganisms)in the baking industry for making breads, pastries and cakes.

Commercial use of microorganisms:-

• 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. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice, crushed fruit juice, etc.
• This is the smell of alcohol as sugar has been converted into alcohol. This process of conversion of sugars into alcohol is known as fermentation.

• Louis Pasteur discovered fermentation in 1857.

Medicinal use of microorganisms:-

• Those medicines which kills or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.

• These antibiotic and produced from fungi and bacteria.
• Streptomycin, tetracycline and erythromycin are the some examples of the commonly known medicines which are made from bacteria and fungi.

• Alexander fleming prepared the mould penicillin in 1929.

Vaccine

• When a disease-carrying microbes enters our body, the body produces antibodies to fight the invader. The body also know how to fight the microbes if it enters again. If dead or weekened microbes are introduced into healthy body, the body  fights and kills the invading bacteria by producing suitable antibodies.
• The antibodies remain in the body and we are protected from the distance causing microbes for ever. This is how a vaccine works.
• Several disease including cholera, tuberculoisis, small pox and hepatities can be  prevented by vaccination.

• Edward Jenner discovered the vaccine for  small pox in 1798.

• polio drops are given to the children to protect from the polio under Pulse Polio Programme. Those polio drops gives to children are actually a vaccie.

Increasing soil fertility

• Some bacteria are able to fix the nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility.These microbes commonly called biological nitrogen fixers.

Cleaning the environment:-

• The microorganisms decompose the dead organic waste of plants and animals converting into simple substance. These substance are again used by other plants and animals. Thus microorganisms can be used to degrade the harmful and smelly substance and thereby cleaning of environment.

2.4 HARMFUL MICROORGANISMS:-

Microorganisms are harmful for us in many ways:-

• Disease causing microorganisms in humans.
• Disease causing microorganisms in animals.
• Disease causing microorganisms in plants.
• Food poisoning.

Disease causing microoragnisms in humans:-

• Some of the microorganisms cause disease in humans beings, plants and animals such causing microorganisms are called “pathogens”.

Pathogens enters our body through many ways are listed below:-

• Through air, we breathe.
• Through water, we drink.
• Through food, we eat.

Those disease that  get transmitted by direct contact with a infected person to a healthy person through water, air, food and physical contact are called communicable disease.

example:- choler, common cold, chicken pox and tuberculosis.

• When a person suffreing from common cold sneezes, fine droplets of moisture carrying thousands of virus are spread in the air. The virus may enter a healthy person while breathing and cause infection. There are some insects and animals which acts as carriers of disease causing micorbes.
• Housefly is one of the such carrier. The flies sit on the garbage and animals excretra. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer  the pathogens. Whenever we eats contaminated food is likely to sick.
• Another example of such carrier is female  Anopheles mosquitoes which carries the parasite of malaria (plasmodium). Female Acedes mosquitoes ct as carrier of dengue virus.
• All mosquitoes breed in water. Hence, we should not let water collect anywhere  in coolers , tyres, flower pot etc. By keeping clean and dry we can prevent mosquitoes from breeding.

Disease causing microorganisms in animals:-

• Several microorganisms not only cause disease in humans and plants but also in other animals.
• Examples:-Anthrax is a dangerous human and cattle disease caused by bacterium. foot and mouth disease of catttle caused by virus.

Disease causing microorganisms in plants:-

• Several microorganisms cause disease in plants like, wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.

food poisoning:-

• Food poisoning can be due to the consumption of food spoilt by the microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These makes the food poisoning causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spilt.

2.5 FOOD PRESERVATION

• Microorganisms spoilt our food. Spoiled food emits bad smell and has bad taste and changed colour.

Chemical method:-

• Salts and edible oils are the common chemicals, generally used to check the growth of the microorganisms. Therefore, they are called preservatives.
• Sodium benzoate and sodium metabisulphite are the common preservatives.
• These are also used in Jams and Squashesto check their spoilage.

Preservation by common salts:-

• Common salts has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria.
• Salting is also used to preserve amla, raw mangoes, tamarind, etc

Preservation by sugars:-

• Jams, jillies and squashes are preserved by sugar. Sugar reduces the moisture content which inhabits the growth of bacteria which spoil food.

Preservation by oil and vinegar:-

• Use of oil and vinegar prevent the spoilage of pickles because bacteria cannot live in such an environment.
• Vegetables, fruit, fish and meat are often preserved by this method.

Heat and cold treatment:-

• Boiling kills many microorganisms. Similarly, we keep our food in refrigerator. Low temperature inhabits the grpwth of microbes.
• Pasteurised milk can be consumed without boiling as it is free from microbes. The milk is heated to about 70oC for 15 cto 30 seconds and then suddenly chilled and stored. By doing. So it prevent the growth of microbes.
• This process was discovered by Louis Pasteur, It is called pasteurisation.

Storage and packing:-

• These days dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microorganisms.

2.6 NITROGEN FIXATION

• Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses).
• Rhizobium lives in the root nodules of leguminous plants. Such as beans and peas with which it has symbiotic relationship. Sometimes, nitrogen get fixed in the soil through the action of lightening.

2.7 NITROGEN CYCLE

• Cyclic flow of atmospheric nitrogen to the living world and back into the atmosphere. This cyclic flow is called nitrogen cycle.
• Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of protein, chlorophyll, nucleic acid and vitamins.
• The atmospheric nitrogen cannot be taken directly by the plants and animals.certain bacteria and blue green algae present in the soil fix the nitrogen from the atmosphere and convert it into compounds of nitrogen.
• Once nitrogen is converted into there usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plants protein and other compounds. Animals feeding on plant to get these protein and other nitrogen compounds.
• When plants and animals die, bacteria and fungii present in the soil convert the nitrogenous wastes in nitrogenous compounds to be used by the plants again. Certain 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 constant.

• AK Raj..!