Science Chapter 2 Micro-Organisms : Friends And Foe

microscope

atmospheric nitrogen

yeast

bacteria

B.

alcohol

B.

 Streptomycin

A.

female Anopheles mosquito

B.

housefly

C.

growth of yeast cells

C.

fermentation

Microorganisms are very small in size and cannot be seen with naked eyes. A microscope has to be used to see these organisms. 

Microorganisms can mainly be divided into five groups :
(i) Bacteria
(ii) Fungi
(iii) Protozoa
(iv) Algae
(v) Virus

Bacteria like Rhizobium and Blue green algae can fix atmospheric nitrogen in soil.

Microorganisms are very useful to us. They help us in following ways :

(i) Microorganisms help us in food industry. They are used for curdling of milk, preparation of bread, cake, etc.

(ii) Microorganisms are used to produce alcohol at large scale on a commercial basis.

(iii) They are used to produce antibiotics.

(iv) They can act as decomposers and increase the fertility of the soil.

(v) They are also used as preservatives for food items.

(vi) They are used for the production of vinegar. 

(vii) Microorganisms are used to prepare vaccines for various disease.

(viii) They fix the atmospheric nitrogen.

(ix) They are used for the production of cheeze. 

(x) Microorganisms prepare manures by decomposing dead bodies of plants and animals.

Microorganisms can prove very harmful to us, as they cause a number of human, animal and plant diseases. Diseases in humans like common cold, tuberculosis, measles, chicken pox, polio, cholera, typhoid, hepatitis B, malaria, etc. are caused by microorganisms. Some serious diseases like Anthrax is also caused in animals by the microbes. Microbes also cause diseases of plants like blights in potatoes, sugarcanes, oranges etc. They also reduce the yield. Besides causing diseses these microorganisms lead to spoilage of food and even cause food poisoning. Microbes also spoil clothings and products. 

Antibiotics are medicines derived from microorganisms. They stop the growth of harmful or disease causing microbes. Antibiotics are made from fungi and bacteria. Alexander Fleming discovered the antibiotic called Penicillin in 1929. Streptomycin, Tetracycline, Erythromycin etc are some commonly used antibiotics.

Precautions that must be taken while taking antibiotics are
i. Antibiotics should only be taken when advised by a qualified physician and one must finish the course prescribed by the doctor.
ii. Antibiotics should only be taken when needed and in the right dose, otherwise, they become less effective for future use.
iii. Taking atibiotics unnecessarily may kill the beneficial bacteria in the body.

The organisms which cannot be seen with our naked eyes are called micro-organisms.

Bacteria and Fungi.

Very tiny microscopic organisms which reproduce only inside the cells of host organisms like bacterium, plant or animal,  are called viruses.

Viruses can only reproduce inside a host cell. They are regarded as being the dividing line between the living and the nonliving.

Dysentery and Malaria are the two diseases caused by protozoans.

Typhoid and cholera are diseases caused by bacterial.

Single celled microorganisms are :
(i) Bacteria
(ii) Some algae.

Multicellular microorganisms are
(i) Fungi
(ii) Algae

Two groups of microorganisms which live in colonies are: 

(i) Bacteria
(ii) Fungi

Fungi consists of two main groups :

(i) Yeasts
(ii) Mould

Amoeba falls in the protozoa group of micro-organisms.

The process of conversion of sugar into alcohol is known as fermentation. The conversion is brought about by yeast

The medicines which kill or stop the growth of the disease causing micro-organisms are called antibiotics. 

Antibodies are the substances made by our body to fight the invader, when a disease carrying microbe enters into the body. It protects our body from the disease causing microbes and body also remembers how to fight, if the pathogen enters again

.

Vaccine is a preparation of a weakened or dead microbe that upon administration to an individual, stimulates the production of antibodies against the pathogen. The antibodies remain in the body and protect us from the disease causing microbes. 

Vaccination is the administration of a vaccine to stimulate an individual's immune system to develop antibodies against the disease or pathogen.

Pulse Polio Programme.

Mushrooms. 

Antibiotics have no effect on viruses because viruses do not have a metabolism of their own. The antibiotics act by hampering the metabolism of the micro-organism rendering them harmless or killing them. Since the viruses have no metabolism of their own and rely on the host enzyme and machinery thus antibiotics have no effect on them. 

Porphyra.

The process by which atmospheric nitrogen is converted into nitrates which can be utilized by plants by the action of micro-organisms is called nitrogen fixation.

The disease causing micro-organisms are called pathogens.

Female Aedes mosquito.

Foot and Mouth disease.

The method to prevent food material from spoilage is called food preservation.

The substances which are used to check the growth of micro-organisms and prevent the spoilage of food, are called food preservatives. Substances like sugar, salt, oil or vinegar or other chemicals are used for this purpose.

The method of food preservation by using certain chemical substances is called chemical preservation. Sodium benzoate is used as a preservative.

Two common preservatives which are available in kitchen are:
(i) Salt
(ii) Oil

The relationship between two organisms in which both the organisms are benefitted is called symbiotic relationship. For example - Rhizobium and roots of legume plants.

Microorganisms thrive in almost all kinds of environments. They are present in air, water, soil and even inside the body of animals and plants. They can be found in extreme environmental conditions like extreme hot, cold or rainy climate. They may be present in hot springs, ice cold water, waters with high salt contents and organic matter, desert soil or even marshy land.

Major groups of microorganisms are :
(i) Bacteria : They are single celled microorganisms.

(ii) Fungi : They are long thread like unicellular as well as multicellular microorganisms.

(iii) Algae : Aquatic, photosynthetic organisms commonly called sea weeds.

(iv) Protozoan : They are unicellular organisms.

(v) Virus: They are non-cellular microbes which only get active inside a living cell.

Viruses are the microorganisms that have the characteristics of both the living and non-living things. They reproduce only inside the cells of host organism, which may be a bacterium plant or animal. Some diseases like cold, influenza, polio and chicken pox are caused by viruses.

Under unfavourable conditions of temperature and water, they generally form a hard and tough covering called cyst or spore. This covering protects them from the harsh conditions. The covering is shed when favourable conditions appear. 

Blue-green algae can fix atmospheric nitrogen. They fix the atmospheric nitrogen in form of nitrates which can be absorbed by the plants 

Importance of fungi are :

(i) Some fungi are eaten raw as food such as mushrooms.

(ii) Yeast being rich in amino acids and proteins are an important source of food for man and  his farm animals.

(iii) Yeast is also used in the preparation of products like wine and bears from fruit juices or barley. It brings about fermentation of sugars into alcohols and carbon dioxide.

Useful effects of algae and protozoa are :
Algae is used as food, fertilizers and in laboratories. It is also used in medicines and cosmetics.

Protozoa help in decomposition and in treatment of waste materials and sewage.

Some fungi causes diseases and food spoilage. Smuts and rusts are fungi that damage the crops. Ring-worm and athletes foot diseases are caused by fungi. Amanite mushrooms contain poisonous substance. Moulds that appear on bread lead to its spoilage.
Algae are great nuisance as they spoil the drinking water by degrading its quality. Excess growth of algae also blocks the movement of water in channels.

Yeast plays an important role in the baking industry. Yeast produces carbon dioxide during respiration, this carbo-dioxide gas is responsible for the rising of the dough. This is the basis of yeast in the baking industry for making breads, pastries and cakes.

Microorganisms grow on the food materials and multiply. They release toxins in the food and making them unfit for consumption. They break down the food molecules into amines and change the taste, texture and external appearance of food. They also release certain toxins and make the food poisonous. 

(a) (i) Aedes mosquito, (ii) Dengue.

(b) (i) Anopheles mosquito, (ii) Plasmodium, (iii) Malaria.

(c) Female.

(d) Female.

The economic importance of bacteria in agriculture

(i) Nitrogen fixing bacteria, Rhizobium are present in the roots nodules of legumes such as gram and pea. These bacteria fix free nitrogen into nitrates and increase the fertility of the soil.

(ii) Bacteria act as decomposers and help in decomposing the dead plant and animals remains, adding nutrients to the soil. They help in the formation of manure which is used to increase the crop yield. 

Protozoans are single celled animals. Some may be in the form of small clusters of cells or colonies. They live in ponds, rivers, lakes and sea. Some live as parasites in man and other animals. For example - amoeba. 

The vaccine contains dead or weakened pathogens. When vaccine is administered, it stimulated the production of antibodies in the individuals body, against the pathogen. Antibodies stay in the body of the individual and protect them from the pathogen.

Pasteurization is the process in which milk is heated to about 70°C for 15 to 30 seconds and then suddenly chilled and stored. This process was discovered by Louis Pasteur. Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Organisms present around us which cannot be seen with naked eyes are called microorganisms. They are present in soil, water and air.

Microorganisms can be divided into five groups:

(i) Bacteria are the non-green single celled microscopic organisms. They have a rigid cell wall. It has a nuclear material. They are the simple most common form of life on earth. They have different shapes and sizes.

(ii) Algae are aquatic, photosynthetic organisms. In simple terms they are called sea weeds. They range in size, colour. Algae are of green, blue, red and blue-green colours.

(iii) Fungi are both unicellular and multicellular. Moulds, mushrooms etc. are fungi.

(iv) Protozoa are one called living things. They range from 2 to 200 microns. Amoeba, Paramecium, Euglena and Plasmodium etc. are protozoas.

(v) Viruses are the non-cellular microbes. They are smaller than bacteria and multiply only inside a living cell.

Nitrogen Cycle : Nitrogen is one of the most essential constituent of living beings. This is because nitrogen is part of chlorophyll, nucleic acids and vitamins. Plants and animals cannot directly consume the nitrogen present in the atmosphere. This work is done by the algae and bacteria .  They fix the atmospheric nitrogen and converts it into nitrite and nitrate. The roots of the plants consume these nitrites and nitrates from the soil. The nitrogen is used to synthesis amino acid, proteins, etc. in the plants. This in turn is consumed by animals feeding on these plants. The dead bodies of these animals are worked upon by the bacteria and fungi present in soil and lead to their decomposition. They convert the compounds of nitrogen back into nitrates and nitrites. These are further converted into nitrogen gas and released in atmosphere by certain specialized bacteria thus balancing the percentage of nitrogen in atmosphere.

The chemical substances which are used to check or stop the growth of harmful micro-organisms in food and prevent the spoiling of food are called food preservatives . 

Some common food preservatives are :

(i) Salt: Common salt is used to preserve meat, fish, amla, raw mangoes and tamarind etc.

(ii) Sugar : Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture contents which inhibits the growth of bacteria which spoil food.

(iii) Oil : Edible oils are used as preservatives in vegetables and pickles.

(iv) Vinegar: It is used to preserve fruits, vegetables, fish, meat and pickles.

Following indications help us an detecting the spoilage in food :

(a) Odour : When food gives out smell, it is the indication that the bacteria has spoiled the food. 

(b) Discolouration : Growth of microbes on food results in discolouration of food. Black moulds on breads, blue green moulds.

(c) Souring : Sometimes the cooked food starts tasting sour. It is due to the production of acids by the action of certain bacteria.

(d) Sliminess : Sometimes the food becomes slimy. It is also due to action of certain bacteria.

(e) Gas formation : Due to action of bacteria gases like carbon dioxide are produced. They also spoil the food by making it swell or become spongy.

Disease causing microbes are some insects and animals which carry the disease causing micro-organisms like housefly, mosquitoes. Such insects and animals are called carriers of disease causing microbes.
Examples:-

(i) Housefly : The housefly is a carrier of micro-organisms. They sit on the garbage and animal excreta. The pathogens stick to their bodies, when these flies sit on uncovered food, they may transfer the pathogens. 

(ii) Female Anopheles Mosquito : It is the carrier of the parasite of malaria.

(iii) Female Aedes mosquito acts as carrier of dengue virus.

The given figure shows the virus.

The most common disease caused by the virus is Polio.

The bacteria live in these roots is Rhizobium.

disease

anaerobic

mushroom

Amoeba

Penicillin.

Sodium benzoate

protozoans

viruses

toxins

fungi

B.

Fungus

B.

insect

A.

Protozoa

B.

Female Aedes Mosquito

C.

Fungi

C.

Bacteria and Fungus

B.

help in fixation of nitrogen

B.

Alcohol

C.

Protozoa

D.

Protozoa