CBSE Class 8 Science Microorganism Friend Or Foe Notes

CBSE Class 8 Science Microorganism Frind and Foe Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

MICROORGANISMS : FRIEND AND FOE

INTRODUCTION
r Microorganisms: The living organisms which cannot be seen by naked eyes and can be seen only through a microscope are called microorganisms or microbes.
• The branch of biology which deals with the study of microorganisms is known as microbiology.
• Father of Microbiology-Louis Pasteur
• The microorganisms include bacteria, fungi, viruses, algae and protozoans. Microorganisms may be unicellular like bacteria, some algae and some fungi and protozoa, or multicellular such as algae and fungi.

OCCURRENCE OF MICROBES
• 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 inside the bodies of animals including humans.
• Some microorganisms grow on other organisms while other exist freely.
• Microbes can live alone, while fungi and bacteria may live in colonies.

MILESTONE IN MICROBIOLOGY
Antony van Leeuwenhoek (1632-1723) born in Holland, was the first person known to have viewed microbes with the help of self designed microscope. He discovered bacteria first, and then red blood cells, yeast in dough, sperm cells and many unicellular organisms. He drew a sketch of each tiny object he viewed and described its source, shape and structure to the best of his understanding.

MICROSCOPES
There are two types of microscopes – a light microscope, which is commonly used in a school laboratory and an electron microscope. In a compound (light) microscope one of the two lenses used is as an "eye piece" and the other as an "objective". Eye is kept over the 'eye piece' and the object to be viewed is kept under the 'objective' on a transparent glass plate on the dias or the stage. This way the image of the object being viewed is magnified upto a thousand times.

Electron microscope is a special type of microscope that uses beams of electrons instead of light, to provide magnification. Magnetic fields are used to bend the electron beams, just as rays of light are bent by the refractive power of a glass lens. Virus could be identified only through an electron microscope.

REVIEW QUESTIONS
1. What are microorganisms?
2. Define microbiology.
3. ______is known as father of microbiology.
4. Which type of microscope is commonly used in school laboratory?
5. Who is Antony van Leeuwenhoek?

GROUPS OF MICROORGANISMS
(A) Bacteria (B) Virus (C) Algae (D) Fungi (E) Protozoa

BACTERIA
• Bacteria were first observed in rainy water and later in teeth scum by Leeuwenhoek and he called them "animalcule".
• Cohn and Ehrenberg first of all coined the name "bacteria".
• Study of bacteria is known as bacteriology.
• They are basically unicellular but can exist as a chain or group of cells.
Occurrence : Bacteria are ubiquitous i.e., they occur anywhere and everywhere, in water in air, in soil and in all living organisms.
Size : Bacteria are very small organisms which are barely visible under the light microscope. Their sizes vary from 0.2 to 100 μ (micron) (1 micron = 10–6 meter).
1. Smallest bacterium = Haemophilus influenze
2. Largest bacterium = Epulospiscium fishelsoni
3. Longest filamentous bacterium = Beggiatoa mirabilis

BACTERIAL CELL STRUCTURE

• Bacteria are unicellular microorganisms.

• They have a primitive cell structure.

• Each bacteria cell has rigid cell wall around it.

• There is no well-developed nucleus but chromatin or nuclear or genetic material or chromosome or DNA is found scattered in the jelly-like granular substance known as cytoplasm present inside the cell. This kind of nucleus is described as incipient nucleus or nucleoid. 

• Membrane bound cell orgenelles e.g. mitochondria, chloroplast, endoplasmic reticulum etc. are not present.

• Bacteria may or may not have thread like structures called flagella. Flagella help bacteria to move.

• Plasma membrane may infold into cytoplasm, this infold is known as mesosome.

• In some bacteria, a slime layer or capsule is present on their cell wall. These are secreted by the bacterial cells. When the secreted material is not compact, it is called a slime layer. But when the material is compact, it is called a capsule.

¶ The Gram staining technique was developed by a Danish scientist, Christian Gram. On the basis of their reactions to a stain, called Gram stain, bacteria are of two types –

Gram positive and Gram negative.

Gram positive bacteria retain the stain while the Gram negative ones do not. The two types of bacteria primarily differ in the structure and composition of cell wals.

• Gram positive bacteria - Salmonella, Spirillum, Escherichia coli.

• Gram negative bacteria - Staphylococcus and Streptococcus.

¶ Nutrition in Bacteria : They lack chlorophyll. They are unable to synthesis their own food as the green plants do. Most of the bacteria are heterotrophs though a few are autotrophs.

(i) Heterotrophic bacteria : They obtain their food from other sources. Depending upon the source, they are:

(a) Saprophytes : These bacteria live on dead organic matter from plants and animals. While living as saprophyte they also cause the decay of the dead organic matter.

(b) Symbionts : They live in association with other living organisms for mutual benefit. e.g. Rhizobium living in the root nodules of leguminous plants.

(c) Parasites : These bacteria live on living plants and animals (hosts) for food and multiplication.While living as a parasite they may also cause illness in the host.

(ii) Autrophic bacteria : They are of two kinds :–

(a) Phototrophs : Making use of sunlight as a source of energy.

• e.g. Purple sulphur bacteria, green sulphur bacteria

(b) Chemotrophs : They oxidise chemicals (inorganic substances) to obtain energy for synthesising food.

• e.g. sulphur bacteria, iron bacteria, nitrifying bacteria.

¶ Respiration in bacteria : On the basis of respiration bacteria are of two types-

(i) Aerobic bacteria : They have capacity of aerobic respiration.

(Respiration in the presence of air (oxygen))

e.g. Azotobacter, Acetobacter, Clostridium

(ii) Anaerobic bacteria : They do not have capacity of aerobic respiration. Respiration in absence of air (oxygen).

e.g. Clostridium botulinum.

¶ Reproduction in bacteria : Bacteria reproduce by three methods-

1. Vegetative reproduction : (a) Budding (b) Binary fission.

2. Asexual reproduction : (a) Endospore formation (b) Cyst formation

3. Genetic recombination : (a) Transformation (b) Conjugation (c) Transduction

Competition Window

Binary fission : In binary fission one cell divides into two, two into four, four into eight and so on. The process of fission is rapid, each fission taking nearly 20 minutes to complete. Binary fission takes place under favourable conditions when sufficient food and water is available temperature.

Endospore formation : Spore formation takes place only at the approach of unfavourable conditions such as shortage of food and water and extreme variations in temperature. While forming a spore the cell contents move towards one side forming a round mass which gets surrounded with a thick protective wall. This is spore. Spore undergoes rest and is able to overcome unfavourable condtions. Spore is able to survive in ice, in boiling water, under dry conditions and in the absence of food. At the approach of favourable conditions the spore germinates and multiples rapidly by binary fission.

IMPORTANCE OF BACTERIA

¶ Retting of Fibres : Fibres from certain plants are obtained by submerging the stems in water for variable periods. The fibres are acted upon by the bacteria growing in water, and the fibres are set free from the stem.

¶ Curing of Cheese, Tobacco and Tea : The flavour of cheese, tea and tobacco depends upon the type fermentation that it has undergone. The process is known as curing and is brought about by different species of bacteria.

¶ Production of Vinegar : Ethyl alcohol is converted into acetic acid (vinegar) by the action of aerobic bacteria, like Acetobacter.

¶ Formation of Curd (dahi) : Making of curd is a process in which the lactose (milk sugar) of the milk is converted into lactic acid by the action of certain bacteria (mainly Lactobacillus).

¶ In medicines : Many antibiotics are obtained from bacteria. example. streptomycin, aureomycin, chloromycin etc.

• Vitamin B is synthesised by bacterium Escherichia coli in the alimentary canal of human beings.

• Bacteria are used in the preparation of vaccines.

MILESTONE IN MICROBIOLOGY

Dr. Edward Jenner a British Physician was the first person to discover the small pox vaccine in 1798. He found that milkmaids who had cowpox, did not get small pox. So, he took some fluid from a cowpox sore and put it on a scretched surface of a healthy boy's arm. The boy did not develop smallpox. He had acquired immunity to smallpox. The fluid from cow-pox was termed as vaccine (Latin vaccin meaning cow). The process of injecting vaccine is a healthy person is termed as vaccination. Resistance to disease for the furture is called immunization.

• Vaccine is a suspension of inactivated pathogens or antigenic protein of pathogen.

• Every organism has a variety of defence mechanism against the disease causing organism like bacteria, fungi viruses etc.

• When a disease carrying microbes 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.

• Antibiotics : Antibiotic is a substance produced by a living organisms which is toxic (poisonous) for other living microorganisms. The source of antibioticsis microorganisms (mainly bacteria and fungi).

MILESTONE IN MICROBIOLOGY

In 1929, Alexander Fleming was working on a culture of disease causing bacteria. Suddenly he found the spores of a little green mould (Penicillium notatum) in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this the mould penicillin (an antibiotic) was prepared.

¶ In Agriculture (Increasing soil Fertility)

• Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.

• These microbes are commonly called biological nitrogen fixers.

• Preparation of organic manure by decay and decomposition of farm and food waste and animal droppings by nitrifying bacteria.

• Fixation of nitrogen as nutrition for plants by symbiotic bacterium – Rhizobium.

• Fixation of nitrogen from air by soil bacteria like Azotobacter and Clostridium enrich soil with plant nutrition.

• Release of nitrogen from decaying nitrogenous matter by denitrifying bacterium to complete nitrogen cycle.

¶ Treatment of sewage : Treatment of sewage consists of three steps :

• Primary treatment • Secondary treatment • Tertiary treatment

Primary treatment is a mechanical process by which large suspended and floating materials and removed.

Secondary treatment is a biological process and involves the use of bacteria and other microbes. Aerobic bacteria like Bacillus, Pseudomonas, and Proteus are used for the secondary treatment of sewage.

Tertiary treatment consist of advanced biological, chemical and physical processes. It aims at further purifying waste water and also in its recycling.

¶ Fuel from gobar and animal waste : Farmers are encouraged to taking to biogas plants on their farms for making use of animal waste in obtaining fuel gas for kitchen and manure for use in the fields. Biogas plants also help in keeping the environment clean. In a biogas plant cattle during and other waste is poured into the digestor where it is decomposed by bacteria and other microbes to evolve fuel gas (methane). The sludge (manure) left behind is taken out and used as manure.

¶ Ruminants, such as cows, buffaloes, sheep, goats, have bacteria in their digestive system which help in the digestion of cellulose, that is, the fibrous part of food.

 Cleaning the Environment :
• 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 cleanup the environment.
• The plant waste can convert into manure by the action of microbes.

DO YOU KNOW?
The human hormone insulin is obtained from bacteria. Earlier it was obtained from cattle and pigs and was very expensive. Large amounts of insulin are produced by bacteria and can be separted easily.

REVIEW QUESTIONS
1. Write the modes of reproduction in bacteria.
2. Explain different shapes of bacteria by giving examples and suitable diagrams.
3. Explain the structure of bacterial cell with the help of a suitable diagram.
4. How are bacteria useful to us?
5. Name the bacterium which helps in curd formation
6. What are Gram positive and Gram negative bacteria?
7. Define antibiotics.

VIRUS

• Term virus is coined by Louis Pasteur.
• In Latin, virus meaning poison.
• Viruses are composed of two types of substances, protein and nucleic acid (either DNA or RNA).
• They are seen only with the help of electron microscope.
• Virion is completely assembled and infectious virus outside its host cell.
• The study of virus is called virology.
• Their sizes vary from 0.015 micron to 0.2 micron.
• The credit for the discovery of viruses goes to Russian botanist Ivanowski. He reported that the cause of disease was not bacterium but some other smaller particle, known as virus.
• Stanley crystallized T.M.V. and showed that crystals retained their infectivity even when stored for a indefinite period in a bottle. 

 Characters of virus :
• Virus consist of nucleic acid and protein.
• The DNA or RNA is surrounded by a protein coat.
• They can only reproduce inside the cells of the living things. They take over these cells and turn them into virus factories which proudce hundreds of new viruses before the cells are killed.
• Virus may be rod-shaped, polygonal, spherical or cuboidal. 

Virus have an important position in comparative study of living and non-living because they show characters of both.

(A) Characters of non-living -
• They can be crystallized.
• They do not have protoplasm
• They do not respire.
• They do not have enzyme system.

(B) Characters of living beings :
• They replicate, although inside the living cells.
• Nucleic acids presents in their body, are capable of synthesizing protein for their coat.
• They cause disease.
• Virus have antigenic character.
 Viruses are named after the disease they cause in plants and animals.
Competition Window
 Viroids : • Viroids are the smallest infectious agents known.
• Viroids (meaning "virus-like") were discovered by the American scientist O. Diener in 1971; the first described viroid was Potato Spindle Tuber Viroid (PSTV).
• Viroids are small fragments of single stranded circular RNA molecules.
 Prions or Slow Viruses : • Prions are proteinaceous infectious particles through to cause a number of diseases.
• Stanley B. Prusiner (United States) won the 1997 Nobel Prize for his discovery of prions and their role in Alzheimer's and mad cow diseases.

DO YOU KNOW?
AIDS
Acquired Immuno Deficiency Syndrome is caused by the Human Immuno-deficiency Virus or HIV. The virus attacks the white blood cells which help to protect the body against diseases. AIDS was first recognized in 1981 and there are now 18 million people in the world known to have HIV. Most are in North and South America, Central Africa and Western Europe. There are also increasingly large numbers in Asia. AIDS is a significant cause of death in men and women under the age of 45 and of children under 5.
Scientists are trying to find a cure, and a vaccine to protect people against HIV. Information and education about HIV and AIDS are important in the fight against the disease.

REVIEW QUESTIONS
1. Write the non living characters of virus.
2. Write the living-being characters of virus.
3. What do you mean by word 'virus'?
4. Classify viruses on the basis of their host.
5. Define bacteriophage.

FUNGI
• Fungi are non green plants.
• Study of fungi known as - mycology
• The outer most covering (cells wall) is made up of chitin.
• The variety of habitats of fungi are damp clothes, old shoes, moist tree trunks, leather goods and food products like bread and cheese. Fungi grow best in dark, warm and moist places.
• Fungi may also be unicellular and multicellular. Unicellular fungi include Yeast and mildews.
• Yeasts live in colonies and are aerobic as well as anaerobic.
• Mildews are parasitic, which grow on some living plants such as potatoes, wheat, grapes, etc.
• Multicellular fungi comprise Moulds and mushrooms.
• Moulds look like a tangled mass of thread-like structure. The mass is called mycelium and the threads are called hyphae. Under the hand lens, tiny dots are observed all over the moulds. These dots are called sporangia, and contain spores.
• Mushrooms are often found growing on wood, and it is common to see them growing on wet soil in shaded places during the rainy season. They also grows by forming mycelium, but those lie under the surface of the soil.
• The umbrella shaped structure is known as the fruiting body of the fungus. Under the umbrella, some slit like structures. They are known as gills; they contain the spores.
• Fungi are heterotrophs either saprophytic or parasitic.
• Saprophytic fungs obtain their food from dead and decaying organic matter.
• The parasitic fungi derive their nutrition by living inside or on the body of another organism.
• Reproduction in fungi takes place by asexual methods, viz., by budding and spore formation.
• Yeast reproduces by budding and forms a colony.
• Certain types of moulds, mildews and mushrooms reproduce by spore formation. 

Importance of Fungi :
(A) In medicines : Many antiboitics are obtained from fungi e.g. Penicillium notatum,
(B) In industry :
(i) Brewery and bakery : In this industries, which make the use of fungus (yeast).
(ii) Cheese industry : Various species of Penicillium are used.
(iii) Vitamins : Formation of vitamin B complex by yeast.

(iv) Organic Acids :
(a) Gallic Acid : Obtain by Aspergillus gallomyces
(b) Citric acid : Obtain by Aspergillus niger
(c) Fumaric Acid : Obtain by Rhizopus and mucor.
(v) Enzymes : Invertase, sucrase, zymase and maltase are obtained from yeast.
(C) In agriculture : Many fungi use in increased soil fertility e.g. Aspergillus, Cladosporium, Penicillium, Rhizopus etc.
(D) As a food :
(a) Some fungi are used as food. e.g. Morchella, Agaricus, Ramaria, Clavaria and Plurosus.
(b) Yeast used in bread formation.

REVIEW QUESTIONS
1. What is the mode of nutrition in fungi ?
2. What are fungi ?
3. Describe different types of fungi.
4. How are fungi important to us?
5. Explain the structure of fungi

ALGAE
• They may be unicellular or multicellular, filamentous or branched.
• Some algae form colonies.
• Algae are eukaryotic, autotrophic and non vascular thallophytes.
• The study of algae is called phycology or algology.
• Algae are found almost everywhere.
• Storage food in algae is starch 

Importance of Algae :
(i) In medicine : As a antibiotics e.g. chlorella
(ii) In industry : As a algal product e.g. Agar-Agar is formed by Gelidium and Gracillaria.
(iii) In agriculture :
(a) Nitrogen fixation : Nostoc, Anabaena, Aulosira, Plectonema are used in nitrogen fixation.
(b) As a manure : Some algae are used as a manure. e.g. Fucus, Sargassum, Macrocystis etc.
(iv) As food: Many algae used as food. e.g. Ulva, Chondrus, Laminaria, Porphyra, Chorella, Spirulina etc. 

REVIEW QUESTIONS
1. What are algae ? Where would you find them growing ?
2. Give the names of algae which used in nitrogen fixation.
3. Give the names of algae which used as a food.
4. What is the mode of nutrition in algae ?

BLUE GREEN ALGAE
These are single celled or multicellular also blue-green in colour. Some cells in multicellular forms are modified to perform a special function nitrogen fixation. The modified cell is called heterocyst. Blue-green algae resemble bacteria in respect. For this reason, these algae are also called cyanobacteria. Both have a primitive cell structure lacking membrane-bound cell organelles and a well defined nucleus.
Reproduction in blue-green algae is common by binary fission or by fragmentation (asexul reproduction).

DIATOMS
Diatoms are golden-brown algae rich in marine places. These algae have various designed bodies impregnated with glass-lime silic. They may be unicellular, colonial or filamentous. the cell wall consists of two overlapping halves hence named as diatom. Diatoms after their death leave large amounts of silica deposits called diatomaceous earth. This being rough, it is used for polishing and in making filtres.
e.g. Navicula, Pinnularia, Cyclotella.

MYCOPLASMA
Mycoplasma is also microorganisms. They lack a cell wall and are very small spherical structure. They often form irregular or oval colonies. Mycoplasmas are parasitic or saprophytic and cause diseases like pleuropneumonia in animals and witches broom in plants. They are resistant to a large number of antiobiotics like penicillin, vaucomycin and cephalosidine, but are sensitive to tetracycline.
Rickettsias are a group of organisms which are parasitic. They grow and reproduce by binary fission inside the host cell. These organisms look like spherical or rod shaped bacteria and are non-motile.

DO YOU KNOW?
Diatoms are a kind of algae that have box-like shapes. They float in the sea all over the earth and have beautiful markings, so they are called 'Jewels of the Sea'. They are an important source of food for many animals.

PROTOZOA
• Protozoa are unicellular eukaryotic organism.
• They are found in water, moist soil and also in other animals.
• They can be free living, symbiotic or parasitic.
• They reproduced by asexual means like budding, binary fission or spore formation.
• Size of protozoan → 2 to 200 microns.
• They are found in irregular shpae, leaf like, elongated etc.
• Locomotion of protozoan takes place by cilia, flagella or pseudopodia.
• Several protozoa cause diseases in man and other animals.
• Structure : Protozoans are non-green unicellular organisms with cell membrane enclosing cytoplasm nucleus,
mitochondrial and other cell organelles. They do not possess a cell wall.
• Euglena is the only one protozoan which is green and includes chlorophyll.
• Amoeba has protoplasmic projections called peudopodia which helps amoeba in locomotion and ingestion of food. Euglena has a single flagellum and Paramecium has cilia all around its body cell. Plasmodium
(which causes malaria disease) is sickle shaped and it slides easily into the cell or the body of the host. 

Importance of Protozoa.
• They act as a link in the food chain.
• They help in the final degradation of waste and sewage.
• They are used as scientific research materials.

REVIEW QUESTIONS
1. What are protozoa?
2. Which type of locomotary organ found in protozoans ?
3. Write full form of PPLO.
4. Give few examples of protozoa

HARMFUL MICROORGANISMS (AS A FOE)
• Disease-causing microorganisms are called pathogens.
• Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. e.g. cholera, common cold, chicken pox and tuberculosis.

MILESTONE IN MICROBIOLOGY
Louis Pasteur : In 1857, he discovered fermentation (The conversion of sugar into alcohol with the help of microbes). 

He developed the method "pasteurization" to preserve milk and liquid food.
He prepared vaccines for anthrax, chickenpox, chicken cholera and rabies.
He was the first who stated the microbes cause diseases. (Germ Theory of Disease).

Robert Koch : In 1876, he discovered the bacterium (Bacillus anthracis) which causes anthrax disease. This led to establish the "Germ Theory of Disease. 

In 1882, he proved that the bacterium Mycobacterium tuberculosis is the main causes of
tuberculosis.

 Food Poisoning : Microorganisms that grow on food some times produce toxic substances. These make the food poisonous causing serious illness and even death.
 How to detect food spoilage
(i) Odour : Repulaive odours or smells
(ii) Putrefaction : The decomposition of organic matter, specially protein by microorganisms, resulting in the production of foul-smelling matter
(iii) Sliminess : Fod surfaces sometimes become slimy due to bacterial growth.
(iv) Discolouration : Microbial growth may result in discolouration of food.
(v) Souring : Food items may taste sour due to the production of acids by certain bacteria.
(vi) Gas formation : Bacteria and yeasts often produce gaseous by products that can affect the texture of food items.

FOOD PRESERVATION
• The process of treating and handling food with an aim to stop or slow down its spoilage while maintaining its nutritional value, texture, and flavour.
• The main cause of spoiling of food products are microorganisms like bacteria and fungi. Where ever they get proper conditions of food, moisture and temperature they start growing. can be preserved food materials, by controlling temperature and moisture.
• Self life is the length of time a product may be stored such that it remains suitable for use or consumption.
• The various methods of food preservation are based on either of the following two basic approaches :

(a) Bacteriocidal Method : The microorganisms responsible for spoilage are full eliminated using some suitable techniques. e.g. cooking, canning.

(b) Bacteriostatic Method : Conditions are created that are not suitable for the growth and action of microorganisms. e.g. salting, packing, deep freezing.

The methods of food preservation :
(i) Heat and cold treatment : Boiling of milk and liquid food products kills many microorganisms. Similarly low temperature inhibit the growth of microbes.
Pasteurisation : This method developed by scientist Louis Pasteur, is used to store milk and liquid food products.
Heating the food up to 60°C for 30 minutes or 70°C for 15 to 30 seconds and then suddenly chilled and stored.
Low temperature Storage : Microorganisms present in food proudcts can not be destroyed by low temperature
but their metabolic activities can be arrested. So that they can't act on food proudcts at –10°C to –18°C temperature. fruits, eggs and meat can be stored for long time.
Refrigeration : Fresh fruit, vegetables, fish, meat, eggs, etc. can be stored by keeping the temperature below 5°C.

(ii) Chemical Method : Salt edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. The commonly used preservatives are sodium benzoate and potassium metabisulphite. This method is employed in the preservation of fruit juice, jams, squashes, fruits, etc.

(iii) Preservation by common salt : Common salt has been used to preserve meat and fish for ages. Concentrated solutions of common salt can kill microorganisms due to dehydration. Salting is also used to preserve amla, raw mangoes.

(iv) Preservation by sugar : Sugar reduces the moisture content which inhibits the growth of bacteria. Jame jellies and Squashes are preserved by sugar.

(v) Preservation by oil and vinegar : Use of oil and vinegar prevents spoilage of pickle because bacteria cannot live in this environment. Vegetables, fruits, fish and meat are often preserved by this method.

(vi) Preservation by radiation : In this method air tight packed food substances, are passed through a radiation beam, microorganisms present in food substances get destroyed due to radiation. This method is a new and cheaper.

(vii) Storage and Packing : Dry fruits and vegetables are sold in sealed air tight packet to prevent the attack of microbes.

Advantages of Food Preservation :
1. The prevents the food from being spoiled by the action of microorganisms.
2. It increases the storage period of food materials.
3. It helps in obtaining the off-season food materials.
4. It makes the transportation of food materials easier.

NITROGEN CYCLE
• Nitrogen is essential component of amino acid, protein, chlorophyll, nucleic acids, vitamins and enzyme. Our atmosphere has 78% nitrogen gas. But it cannot be used directly and is changed free nitrogen into nitrites and nitrates and then utilized.
• Nitrogen cycle has following steps :

(A) Nitrogen fixation : It involves the conversion of free nitrogen into nitrite and nitrates.
Nitrogen fixation in divide in two types - 

(B) Ammonification : Ammonifying bacteria convert the protein (present in decaying plant and animals) into ammonia.
e.g. Bacillus vulgaris, Bacillus mycoides, Bacillus ramosus, Bacillus subtilis

(C) Nitrification : Nitrifying bacteria convert the ammonia to nitrite and later into nitrate
NH3 (Ammonia) ⎯⎯Nit⎯ro⎯so⎯mo⎯na⎯s⎯→ NO2–(Nitrite) ⎯⎯Nit⎯ro⎯ba⎯cte⎯r⎯→ NO3–(Nitrate)

(D) Denitrification : Denitrifying bacteria convert the ammonium compound, nitrites and nitrates to molecular nitrogen.
e.g. Thiobacillus denitrificans 

REVIEW QUESTIONS
1. What is food preservation ?
2. Write the method of pasteurisation.
3. What is nitrogen fixation ?
4. Write name of the bacteria which occur freely in soil and do nitrogen fixation.
5. Write name of the bacteria which live symbiotically and do nitrogen fixation.

EXERCISE-1

Question. Pasteurization means -
(A) Vaccination for a baby against smallpox.
(B) Sterilization in steam cooker at 100° C.
(C) Heating milk or other liquids to 60°C to 70°C for short duration.
(D) A technique or curing people bitten by mad dogs.
Answer : C

Question. Bacteria differ from other plants in that they do not have.
(A) DNA
(B) RNA
(C) Cell wall
(D) A well defined nucleus
Answer : D

Question. Who proposed the germ theory of disease?
(A) Robert Koch
(B) A.Fleming
(C) E. Jenner
(D) Louis Pasteur
Answer : D

Question. Comma shaped bacteria are termed as -
(A) Bacilli
(B) Cocei
(C) Spirilla
(D) Vibrio
Answer : D

Question. Food spoilage can be prevented by -
(A) Healing of food
(B) Using chemicals
(C) Canning
(D) All of these
Answer : D

Question. Yeast is used in the production of
(A) Sugar
(B) Alcohol
(C) Hydrochloric acid
(D) Oxygen
Answer : B

Question. The fixation of free nitrogen by bacteria in the soil is done by-
(A) Azotobacter
(B) Nitrosomonas
(C) Nitrobacter
(D) Thiobacillus
Answer : A

Question. Nitrifying bacteria convert the-
(A) Nitrates into nitrites
(B) Ammonium salts into nitrates
(C) Ammonium salts into amino acids.
(D) All of the above
Answer : B

Question. The bacterial genome is called :
(A) Nucleus
(B) Nucleolus
(C) Nucleoid
(D) None
Answer : C

Question. Antibiotics are mostly obtained from-
(A) Bacteria
(B) Viruses
(C) Angiosperms
(D) Fungi
Answer : A

Question. Nitrates are converted into nitrogen by-
(A) Denitrifying bacteria
(B) Nitrifying bacteria
(C) Ammonifying bacteria
(D) Nitrogen fixing bacteria
Answer : A

Question. All bacteria have the following organelle.
(A) Mesosomes
(B) Golgibodies
(C) Mitochondria
(D) Chloroplast
Answer : A

Question. Rounded bacteria are-
(A) Bacilli
(B) Vibrio
(C) Spirilla
(D) Cocci
Answer : D

Question. The following is an antibiotic
(A) Sodium bicarbonate
(B) Streptomycin
(C) Alcohol
(D) Yeast
Answer : B

Question. Virus possess-
(A) DNA only
(B) Nucleic acid, DNA or RNA
(C) Protein only
(D) Nucleic acid and protein
Answer : B

Question. Capsid is-
(A) Genetic material of virus
(B) Protein cover of virus
(C) Extra genetic material of bacterium
(D) Genome of bacterium
Answer : B

Question. Carrier of malaria-causing protozoan is
(A) Female Anopheles mosquito
(B) Cockroach
(C) Housefly
(D) Butterfly
Answer : D

Question. Who discovered vaccination against small pox.
(A) Jenner
(B) Pasteur
(C) Lister
(D) Mayer
Answer : A

Question. Bacteriophage is-
(A) Virus attacking bacteria
(B) Virus attacking virus
(C) Bacterium attacking virus
(D) Stage in bacterial life cycle
Answer : C

Question. The most common carrier of communicable diseases is –
(A) Ant
(B) Housefly
(C) Dragonfly
(D) Spider
Answer : B

Question. Elephantiasis is caused by :-
(A) Anopheles mosquito
(B) Culex mosquito
(C) tsetse fly
(D) Plasmodium
Answer : B

Question. Bacteria bearing flagella all over body are-
(A) Peritrichous
(B) Atrichous
(C) Monotrichous
(D) Cephalotrichous
Answer : A

Question. BCG stands for :
(A) Bacillus carol gram
(B) Bacillus Chalmette Guerin
(C) Bacteria Chalmette Guerin
(D) None of the above
Answer : B

Question. Thread like fungal structure are-
(A) Hyphae
(B) Mycelium
(C) Rhizomorphs
(D) Sclerotia
Answer : A

Question. Fungal cell wall is composed of-
(A) Chitin
(B) Hemicellulose
(C) Cellulose
(D) None of these
Answer : A

Question. Fleming discovered penicillin from-
(A) Penicillium notatum
(B) Penicillium roqueforti
(C) Penicillium camemberti
(D) Penicillium chrysogenum
Answer : A

Question. Yeast are economically important because they-
(A) Spread plant diseases
(B) Spread animal diseases
(C) Are used in tea and tobacco industry
(D) Are used in wine and baking industry
Answer : D

Question. The bread or idli dough rises because of –
(A) Heat
(B) Grinding
(C) Growth of yeast cells
(D) Kneading
Answer : C

Question. Botulism is caused by :-
(A) Salmonella typhae
(B) Clostridium botulinum
(C) Crasticium botulinum
(D) Staphylococci
Answer : B

Question. Bacterial infection of food can be prevented by :-
(A) covering the food
(B) keeping the food very cold
(C) heating the food upto 70°C at least
(D) Both (A) and (C)
Answer : D

Question. DPT Vaccine is for :
(A) Diptheria, Polio, Tetanus
(B) Diptheria, Pertussis, Tetanus
(C) Diptheria, Pertussis, Typhoid
(D) Diptheria, Pertussis, Tuberculosis
Answer : B

Question. MMR vaccine is given for :
(A) Malaria, Mumps, Rubeolla
(B) Mumps, Measles, Rabies
(C) Mumps, Measles, Rubeolla
(D) None of the above
Answer : C

Question. Ring worm spreads through :
(A) Contaminated food and water
(B) Direct skin contact
(C) Insects
(D) Contaminated air
Answer : B

Question. World TB day is celebrated on :
(A) March 21
(B) March 24
(C) March 30
(D) March 18
Answer : B

Question. Who discovered antibiotic streptomycin effective against Tuberculosis :-
(A) Selman A. Waksman
(B) Louis Pasteur
(C) Robert Koch
(D) Iwanowsky
Answer : A

Question. Mathch the following pairs
             A                   B
1. Tuberculosis    I. Entamoeba
2. Typhoid          II. Mycobacterium
3. Malaria          III. Plasmodium
4. Dysentery      IV. Salmonella
(A) 1 - III, 2 - IV, 3 - I, 4 - II
(B) 1 - II, 2 - IV, 3 - III, 4 - I
(C) 1 - III, 2 - I, 3 - II, 4 - IV
(D) 1 - IV, 2 - III, 3 - II, 4 - I
Answer : B

Question. In Blue green algae, the structure specialised for nitrogen fixation is
(A) Thylakoid
(B) Harmogonia
(C) Heterocyst
(D) Endospore
Answer : C

Question. The similarity between bacterium and cyanobacterium is in the presence of
(A) Flagella
(B) Nucleoid
(C) Size
(D) 80S ribosomes
Answer : B

Question. Rocky mountain spotted fever is caused by
(A) Rickettsias
(B) Fungi
(C) Bacteria
(D) PPLO
Answer : A

Question. The figure given below shows the method of reproduction of a microorganism.
Which of the following combination is correct ?
Microorganisms Method of reproduction
(A) Viruses Binary fission
(B) Fungi Budding
(C) Algae Conjugation
(D) Fungi Spore formation
Answer : D

Question. Viruses are
(A) Complete saprophytes
(B) Partial saprophytes
(C) Complete parasites
(D) Partial Parasites.
Answer : C

Question. Protein coat of virus is called
(A) Capsomeres
(B) Capsid
(C) Peplos
(D) Nucleoid
Answer : B

Question. Cell organelles that resemble viruses in chemical nature are
(A) Mitochondria
(B) Ribosomes
(C) Plastids
(D) Golgi complex
Answer : B

Question. Mycoplasma differ from bacteria in
(A) Not having a cell wall
(B) Having organised nucleus
(C) Having organised cell organelles
(D) None of the above
Answer : A

Question. Escherichia coli in human intestine synthesises
(A) Vitamin B and D
(B) Vitamin B and C
(C) Vitamin A and K
(D) Vitamin B and K
Answer : D

Question. The smallest bacterium is
(A) Spirochaete
(B) Dialister pneumosintes
(C) Vibrio
(D) Lactobacillus
Answer : B

Question. Bacteria having a tuft of flagella at one end are called-
(A) Peritrichous
(B) Monotrichous
(C) Lophotrichous
(D) Amphitrichous
Answer : C

Question. Saccharomyces cerevisiae is
(A) Baker's yeast
(B) Beer yeast
(C) Both a and b
(D) Wine yeast
Answer : C

Question. Yeast contains maximum amount of
(A) Vitamin C
(B) Riboflavin
(C) Protein
(D) Carbohydrate
Answer : B

Question. Which of the following are represented by P, Q, R and S in figure given below ?
(A) P - Diatom, Q - Chlamydomonas, R - Spirogyra, S - Volvox
(B) P - Volvox, Q - Chlamydomonas, R - Spirogyra, S - Diatom
(C) P - Volvox, Q - Diatom, R - Spirogyra, S - Chlamydomonas
(D) P - Spirogyra, Q - Volvox, R - Diatom, S - Chlamydomonas
Answer : A

Question. Contractile vacuole of Amoeba is analogous to
(A) Kidneys
(B) Gastrovascular cavity of hydra
(C) Sweat glands
(D) None of tha above
Answer : A

Question. Virus possessing only proteins are called:
(A) Viroids
(B) Prions
(C) Virons
(D) None of the above
Answer : B

FILL IN THE BLANKS

Question. ________is used in the preparation of beverages by fermentation of barley.
Answer : Saccharomyces cervisiae

Question. A parasitic protozoan ________ causes a disease called 'sleeping sickness'.
Answer : Trypanosoma 

Question. ________ is a type of algae that live in colonies.
Answer : Volvox 

Question. ________ help the Paramaecium to catch its prey.
Answer : Pseudopodia

Question. Blue green algae fix _______ directly from air to enhance fertility of soil.
Answer : Nitrogen 

Question ________ fungus caused famine in ireland in the year 1845-46.
Answer : Phytophthoro infestans

Question. Mico-organisms can be seen with the help of a ________
Answer : Magnifying glass or microscope

Question. Alcohol is produced with the help of ________
Answer : Yeasts 

Question. Algae can prepare their own food becaue they possess ________
Answer : Chlorophyll

Question. Cholera is caused by ––––––––
Answer : A bacterium

Question. ________ bacteria can grow in the absence of oxygen.
Answer : Anaerobic 

Question. Viruses are ________ in size than bacteria.
Answer : Smaller

Question. The fungus that grows on bread is known as________
Answer : Bread mould (Rhizopus)

Question. Bacteria generally reproduce by ________
Answer : Binary fission

Question. The virus which attacks bacteria is called ________
Answer : Bacteriophage

WRITE TRUE OR FALSE FOR THE FOLLOWING

Question. Viruses are useful to making breads.
Answer : FALSE 

Question. Euglena can perform photosynthesis.
Answer : TRUE 

Question. Protozoa are plant-like organisms.
Answer : FALSE 

Question. Virus contains both type of nucleic acids i.e. DNA and RNA.
Answer : FALSE 

Question. Lichen is an alga.
Answer : FALSE 

Question. Bacteria cause foot and mouth disease.
Answer : FALSE 

Question. Cocci are spiral shaped bacteria.
Answer : FALSE 

Question. Bacteria have a well-developed nucleus.
Answer : FALSE 

Question. Spirogyra is a filamentous form of algae.
Answer : TRUE 

Question. Tobacco mosaic is the name of a fungus.
Answer : FALSE 

Question. Milk is preserved by pasteurization.
Answer : TRUE 

Question. Moulds are a type of fungi.
Answer : TRUE 

Question. Study of algae is called phycology.
Answer : TRUE 

Question. Agar is obtained from blue-green algae.
Answer : FALSE 

Question. Malaria is caused by the bite of infected fleas.
Answer : TRUE 

MATCH THE FOLLOWING
(A) Column-A             Column-B
(1) Phycology            (a) An alga
(2) Spirilla                (b) A disease
(3) Chlorella             (c) Study of algae
(4) Measles              (d) Curd making
(5) Bacteria              (e) A kind of bacterium

(B) Column-A                           Column-B
(1) Mycelium                         (a) Slipper shaped
(2) Potato blight                     (b) Plasmodium
(3) Paramaecium                    (c) Jam, jely, etc.
(4) Malaria causing protozoan  (d) Rhizopus
(5) Sodium metabisulphite      (e) Viral disease
(6) Rabies                              (f) Fermentation of molasses
(7) Ethyl alcohol                     (g) Fungal disease

A) (1) → c ; (2) → e ; (3) → a ; (4) → b ; (5) → d ;
(B) (1) → d ; (2) → g ; (3) → a ; (4) → b ; (5) → c ; (6) → e ; (7) → f