microorganisms friend and foe class 8 science pdf

2 MICROORGANISMS
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Introduction
Bacteria
Fungi
Protozoa
Algae
Virus
Food preservation
Nitrogen cycle
2.1 INTRODUCTION
Microorganisms are mostly harmless and non-pathogenic (non-disease
causing), and indeed may be beneficial. It is estimated that a human
body carries approximately 1014
cells, but only 10% of these are human
in origin; the rest is microbial flora. There is not a consensus definition
of a microbe but broadly speaking they are organisms which are not
visible to the naked eye. Medical microbiology is the study of
microscopic organisms and their effect on humans. It encompasses their
biology, diagnosis, treatment and prevention.
2.1.1 Habitats of microbes
They live in almost every habitat from the poles to the equator, deserts,
geysers, rocks, and the deep sea. Some are adapted to extremes such as
very hot or very cold conditions, others to high pressure and a few to
high radiation environments. Microorganisms also make up the
microbiota found in and on all multicellular organisms. Some microbes
live alone while others live in groups or colonies.
The environment and the recent temperature anomalies play a crucial
role in driving changes to the microbial communities. For instance, the
assemblage of microbes that exists on the surface of seawater is thought
to have undergone tremendous change with respect to composition,
abundance, diversity, and virulence as a result of climate-driving sea
surface warming.
Not every microbe can survive in all habitats, though. Each type of
microbe has evolved to live within a narrow range of conditions. Their
diversity also makes them tolerant of many other conditions, such as
limited water availability, high salt content and low oxygen levels.
During unfavorable conditions, microbes remain inactive and form a
hard outer covering around them called cyst. They become active when
favorable conditions resume.
2.1.2 Importance of microbes
Although the vast majority of microbial diversity remains undetermined,
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it is globally understood that the effects of microorganisms on their environment can be beneficial. The
beneficial effects of microbes derive from their metabolic activities in the environment, their associations
with plants and animals, and from their use in food production and biotechnological processes.
Microbes are important in human culture and health in many ways, serving to ferment foods, treat
sewage, produce fuel, enzymes and other bioactive compounds. They are essential tools in biology as
model organisms, and have been put to use in biological warfare and bioterrorism. They are a vital
component of fertile soils. In the human body microorganisms make up the human microbiota including
the essential gut flora. They are also the pathogens responsible for many infectious and communicable
diseases which spread from an infected person to a healthy person.
2.1.3 Types of microbes
Microbes exist as unicellular, multicellular, or cell clusters. They have different characteristics for
example, some have cell walls, some don’t, some are photosynthetic, some are saprophytic, etc. Based on
their similarities and dissimilarities, they can be divided into five major types: bacteria, fungi, protozoa,
algae, and viruses. Earlier, they were grouped into two domain system i.e. prokaryotes and eukaryotes.
All the unicellular microbes i.e. bacteria constitute the prokaryotes while the multicellular microbes i.e.
fungi, protozoa etc. constitute the eukaryotes. Viruses are categorized into any of the two domains.
2.2 BACTERIA
Bacteria are prokaryotic – unicellular, and having no cell nucleus or other membrane-bound organelle.
They are microscopic, with a few extremely rare exceptions. They function and reproduce as individual
cells, but can often aggregate in multicellular colonies. Some species can aggregate into complex
swarming structures, operating as multicellular groups as part of their life cycle, or form clusters in
bacterial colonies. Bacteria are included in the Kingdom Monera (the 1st
kingdom of living organisms)
and are the simplest living organisms on earth.
2.2.1 Habitat
Bacteria are found almost everywhere in both living and non-living environment for example, harsh and
extreme climatic conditions like in hot springs, acidic soils, under ice, in deep ocean floor, in deserts and
on or inside the body of plants and animals etc. The largest number exists in the gut flora, and a large
number on the skin. They can survive drought and heat. They can respire even without oxygen and are
called anaerobic bacteria while those that need oxygen for respiration are called aerobic bacteria.
2.2.2 Shape and size
Due to the presence of a rigid cell wall, bacteria
maintain a definite shape, though they vary as
shape, size and structure. Most bacteria appear in
variations of four major shapes: the rod
(bacillus), the sphere (coccus), the spiral type
(spirilla) and the comma type (vibrio). In fact,
structure of bacteria has two aspects, arrangement
and shape. So far as the arrangement is
concerned, it may be paired (diplo), grape-like
clusters (staphylo) or chains (strepto).

Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0.5–5.0 m in length.
However, a few species are visible to the unaided eye—for example, Thiomargarita namibiensis is up to
half a mm long and Epulopiscium fishelsoni reaches 0.7 mm. Among the smallest bacteria are members of
the genus Mycoplasma, which measure only 0.3 m, as small as the largest viruses.
2.2.3 Cell structure
The bacterial cell is surrounded by a cell membrane (also known as a lipid, cytoplasmic or plasma
membrane). This membrane encloses the contents of the cell and acts as a barrier to hold nutrients,
proteins and other essential components of the cytoplasm within the cell. As they are prokaryotes,
bacteria do not usually have membrane-bound organelles in their cytoplasm, and thus contain few large
intracellular structures. They lack a true nucleus, mitochondria, chloroplasts and the other organelles
present in eukaryotic cells. Bacteria do not have a membrane-bound nucleus, and their genetic material is
typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped
body called the nucleoid. The nucleoid contains the chromosome with its associated proteins and RNA.
Rigid protein thread like structures (about 20 nm in
diameter and up to 20 m in length) called flagella are used
for motility.
In most bacteria, a cell wall is present on the outside of the
cell membrane. A common bacterial cell wall material is
peptidoglycan (called "murein" in older sources), and are
different from the cell walls of plants and fungi, which are
made of cellulose and chitin, respectively. They are
enclosed within a gelatin-like envelope called capsule
which protect cells from engulfment by eukaryotic cells.
2.2.4 Nutrition
Most bacteria can't manufacture their own food and receive them from dead organic matter (saprophytic)
or living organism (parasitic) while other bacteria live in symbiotic relationship with other organisms eg.
E. coli living in the intestine of humans.
Most bacteria lack chlorophyll but still they are able to use chemical energy for own food synthesis. They
are called chemosynthetic autotrophs eg. Nitrosomanas, Nitrococcus. These bacteria oxidise chemical
compounds like sulphur and hydrogen sulphide and release chemical energy which is used for food
synthesis.
There is a certain group of unicellular organisms called cyanobacteria or blue-green algae which can
synthesize food using chlorophyll. They are the first organisms to produce O2 on earth. They are found
mainly in fresh water while few are marines. They occur singly or form colonies eg. Nostoc.
2.2.5 Reproduction
Bacteria grow to a fixed size and then reproduce through binary
fission, a form of asexual reproduction. Under optimal conditions,
bacteria can grow and divide extremely rapidly, and bacterial

populations can double as quickly as every 9.8 minutes. In cell division, two identical clone daughter cells
are produced. Some bacteria, while still reproducing asexually, form more complex reproductive
structures that help disperse the newly formed daughter cells. In some bacteria, multiple fission is
observed which involves the formation of many daughter cells.
2.2.6 Effects of bacteria
Useful effects
 Used in the production of antibiotics for treating infectious diseases.
 Used for vitamin and vaccine production.
 Used in genetic engineering.
 Helps in nitrogen fixation, ammonification and manure preparation.
 Used in the dairy industry - the milk-souring bacterium Lactobacillus bulgaricus is used to make
yoghurt and cheese.
 Used to form organic acids in pickles and vinegar.
 Used to separate fibres of jute, hemp, and flax in the process of retting.
 Used for tanning of hides.
 Some bacteria living in the gut of cattle, horses and other herbivores secrete cellulase, an enzyme that
helps in the digestion of the cellulose of plant cell walls.
 Bacteria can also be used in the place of pesticides in biological pest control eg. Bacillus thuringiensis.
Harmful effects
 Pathogenic bacteria harm human beings by causing diseases like diarrhea, tetanus, diphtheria, jaundice,
tuberculosis, leprosy, pneumonia, typhoid, dysentery, cholera etc.
 Diseases in plants are citrus canker, leaf blight of rice (a soil borne disease), blight of beans etc.
 Diseases in animals are anthrax, tuberculosis in cattles, dogs and parrot, etc.
 Pathogenic bacteria causing anthrax, botulism, cholera, tuberculosis etc. are used in biological warfare
as very strong weapons against the enemy.
 Spoilage of food and food poisoning by Pseudomonas, Escherichia, Salmonella, etc.
 Destroy materials like cork, rubber and cordage; also destroy cellulose, the base of paper.
 Several bacterial forms cause water pollution eg. Vibrio cholerae, Salmonella typhi.
 Destroy soil quality by denitrification.
2.3 FUNGI
Kingdom Mycota contains the achlorophyllus, eukaryotic, spore producing, filamentous organisms i.e.
fungi. They are unicellular or multicellular; aerobic or anaerobic. Study of fungi is called mycology.
2.3.1 Habitat
Fungi are cosmopolitan, terrestrial and aquatic. They prefer dark, warm and damp places to grow. Most
live in either soil or dead matter, and many are symbionts of plants, animals, or other fungi. Fungi, along
with bacteria that are found in soil, are the primary decomposers of organic matter in terrestrial
ecosystems. Woods and meadows are the best habitats; over 80% of known fungi are associated with
trees; many of these fungi form symbiotic relationships with the tree's roots i.e. mycorrhiza. Other fungi,
such as the edible field mushroom, prefer open, grassy places. They can grow on animal dung, burnt
wood, hairs, horns, stale bread, leather goods, poorly preserved food, pickles, etc.

A key characteristic of fungi that has contributed to their successful exploitation of diverse ecological
niches is the formation of a filamentous thallus called mycelium. A mycelium is composed of branching,
microscopic tubular cells called hyphae that grow through and across substrates or food sources, secreting
enzymes that break down complex substrates into simple compounds that can be absorbed back through
the cell wall. The fungal cell wall is composed of chitin and glucans as well as other components.
Hyphae can have cross walls called septa, or lack cross walls
(non-septate/aseptate/coenocytic). The type of hyphae—septate
or aseptate—is characteristic of specific groups of fungi. In
fungi that form septate hyphae, there are perforations at the
septa, called septal pores, which allow the movement of
cytoplasm and organelles from one compartment to the next.
Most organelles present in fungal cells are similar to those of
other eukaryotes i.e. well-developed nucleus and cell organelles. Fungal nuclei are usually small (< 2 µm
diameter), and can compress and/or stretch to move through septal pores and into developing spores.
Unicellular fungi include yeast (colonial, aerobic and anaerobic too) and mildews (parasitic, saprophytic).
Fungi growing on damp clothes and leather goods are often mildews. Multicellular fungi comprise
moulds and mushrooms. Moulds are tangled mass of thread-like structures eg. Penicillium. They grow on
rotten fruits, bread, moist grains, pulses etc. They are one of the fastest growing filamentous fungi
measuring approx. 10 cm. Mushrooms are common in rainy season and grow in shady places such as tree
roots, wood etc. They contain slit-like apertures called gills on their underside; these gills contain spores.
2.3.3 Nutrition
Fungi are achlorophyllous i.e. they lack chlorophyll and are therefore incapable of photosynthesis. They
are either parasitic or saprophytic. Saprophytes release enzymes to break-down dead organic matter into
chemicals that can then be absorbed and processed. They digest their food externally and then absorb the
products of that 'digestion'.
2.3.4 Reproduction
Fungi frequently reproduce by the formation of spores. A spore is a survival or dispersal unit, consisting
of one or a few cells, that is capable of germinating to produce a new hypha. Spores are encased in a hard
protective covering and are formed in sporangium. Other asexual means of reproduction includes budding
and fragmentation. Budding most commonly occurs in yeast where an outgrowth or bud develops from
the parent body and later detaches to form a new individual. Fragmentation involves the breaking of
hyphae with each fragment forming new individuals.
2.3.5 Effects of fungi
Fungi are involved in a wide range of activities—some fungi are decomposers, parasites or pathogens of
other organisms and others are beneficial partners in symbiosis with animals, plants or algae.

Useful effects
 Decomposition and recycling - Fungi decompose plant and animal wastes and return them to the soil in
a form in which it can be reused.
 Yeasts are used in the brewing industry for production of beer and wine. Food yeasts are rich in protein
and vitamins-B.
 Used widely in the production of many foods - cheese, bread, cakes, soya bean products, etc. Many
mushrooms are edible.
 Used for antibiotic production eg. Penicillin
 Control insect pests of crops as certain fungi parasitize insects.
Harmful effects
Fungi cause a number of plant and animal diseases: in humans, ringworm, athlete's foot, and several more
serious diseases. Because fungi are more chemically and genetically similar to animals than other
organisms, this makes fungal diseases very difficult to treat. Plant diseases caused by fungi include rusts,
smuts, and leaf, root, and stem rots, and may cause severe damage to crops.
2.4 PROTOZOA
Protozoa are unicellular aerobic eukaryotes. They make up the largest group of organisms in the world in
terms of numbers, biomass, and diversity.
2.4.1 Habitat
Protozoa diversity is high in oceans, deep sea-vents, river sediment and acidic river; some are even found
in soil. Many protozoans are also endoparasites i.e. parasites inside the body of the living host.
Protozoa ranging in size from 10 - 52 m however, some are significantly larger. Among the largest are
the deep-sea–dwelling single-celled foraminifera whose shells can reach 20 cm in diameter. Free-living
forms are restricted to moist environments, such as soils, mosses and aquatic habitats, although many
form resting cysts which enable them to survive drying.
Shapes vary from irregular (eg. Amoeba) to definite (eg. Paramecium) shapes. The cell is eukaryotic type
with all kinds of membrane bound cell organelles and a well-defined nucleus. Some protozoa can be
uni/bi/multinucleated. They lack cell wall and chlorophyll. The pellicle is a thin layer supporting the cell
membrane in various protozoa, protecting them and allowing them to retain their shape, especially during
locomotion, allowing the organism to be more hydrodynamic.Mode of locomotion involves flagella
(whip-like structure to propel forward), cilia (tiny hair that beat to produce movement), and false feet or
pseudopodia (used for feeding and locomotion). Most sporozoans (a category of protozoans) are non-
motile.
2.4.3 Nutrition
Most protozoa are chemoheterotrophs i.e. organisms using preformed organic compounds for both energy
and carbon. Most do not contain green pigments and are not capable of using light as an energy source
(however there are exceptions). Most protozoa are free-living organisms that obtain nutrients from
decaying organic materials or feed on bacteria and smaller eukaryotic cells. They are parasites,
saprophytic and holozoic.

2.4.4 Reproduction
Protozoa can reproduce both asexually and sexually. Asexual modes of reproduction involves fission
(binary or multiple), budding and spore formation. In order to reproduce sexually, protozoa must interact
with other, genetically different cells. Syngamy and conjugation are two examples of sexual reproduction,
where segments of genetic material (DNA) are exchanged between the two cells eg. Paramecium.
2.4.5 Some common protozoans
Amoeba: They live in fresh water, salt
water, in soil, and as parasites in moist
body parts of animals. They are composed
of cytoplasm divided into a thin, clear, gel-
like outer layer that acts as a membrane
(ectoplasm) and an inner, more watery
grainy mass (endoplasm) containing
organelles. They may have one or more
nuclei, depending upon the species.
Amoeba move by continually changing its body shape, forming extensions called pseudopods into which
its body then flows. The pseudopods also are used to surround and capture food—mainly bacteria, algae,
and other protozoa—from the surrounding water. An opening in the membrane allows the food particles,
along with drops of water, to enter the cell, where they are enclosed in bubble-like chambers called food
vacuoles. There the food is digested by enzymes and absorbed into the cell. The food vacuoles then
disappear. Liquid wastes are expelled through the membrane. Water from the surrounding environment
flows through the amoeba's ectoplasm by a process called osmosis. When too much water accumulates in
the cell, the excess is enclosed in a structure called a contractile vacuole and squirted back out through the
cell membrane. The membrane also allows oxygen to pass into the cell and carbon dioxide to pass out.
Amoebas reproduce by binary fission.
Paramecium: These are unicellular and slipper-shaped organisms
found in freshwater environments, ranging from 50 - 300 μm in
length, depending on the species. Simple cilia, tiny hair-like
filaments, cover the body, and there is a deep oral groove,
containing inconspicuous compound oral cilia. These cilia aid in
both movement and in moving food to the oral cavity. Food enters
the food vacuoles, which cilia push into the gullet in a process
known as phagocytosis, and is digested with the aid of hydrochloric
acid and enzymes. When digestion is complete, the remaining food content is emptied into pellicles,
known as cytoproct. Osmoregulation is carried out by a pair of contractile vacuoles on either end of the
cell, which actively expel water absorbed by osmosis from the surroundings.
Paramecium has two different types of nuclei within their cells i.e. micronuclei and macronuclei. The
latter is responsible for everyday activities including growth and reproduction, and the micronucleus
remains dormant until the cell reproduces. Besides reproducing by binary fission, they also exhibit a
rudimentary sexual reproduction, whereby two parameciums come together, conjugate, and exchange
genetic material. Some species of paramecia also form harmonious, symbiotic relationships with algae,
with algae providing the products of photosynthesis to the paramecia, while receiving a habitat in which
to flourish.

Euglena: They are single celled organisms
that contain characteristics of both animal
and plants. They are both autotrophs i.e. can
carry out photosynthesis and make own
food like plants, as well as heteroptoph i.e.
can also capture and ingest food. When
acting as autotroph, they utilize chloroplasts
to produce sugars by photosynthesis; when
acting as heterotroph, they surround food
particles and consume it by phagocytosis.
Due to this adaptation, many Euglena are considered mixotrophs i.e. autotrophs in the light and
heterotophs in the dark. Locomotion comes in the form of either the rotating flagellums, or the flexible
pellicle membrane. They undergo asexual reproduction by binary fission.
2.4.6 Effects of protozoa
Useful effects
 Protozoans serve as food for many small aquatic organisms. Zooplankton are tiny protozoans which
live in the sea. They form the principal diet of blue whales, who gulp them in with sea water.
 They are the ultimate decomposers in nature, as they feed on bacteria and fungi, which decompose dead
organic matter. They are, thus, useful in the treatment of sewage.
 Some protozoans live in the body of other organisms and help them. Termites, for example, have
protozoans living in their body. The protozoans digest the cellulose in the wood eaten by termites and
convert it into carbohydrates that the termites can use.
Harmful effects: Some protozoans cause diseases. Entamoeba histolytica causes amoebiasis (amoebic
dysentery) in human beings; Giardia causes giardiasis (dysentery), while Plasmodium causes malaria.
Trypanosome, a parasitic protozoan which lives in the bloodstream of human beings, cattle and other
animals, causes a dangerous disease called sleeping sickness.
2.5 ALGAE
Algae are unicellular or multicellular photosynthetic eukaryotes. They are the major food producers of the
aquatic habitat. They live in water, damp soil, and rocks and produce oxygen and carbohydrates used by
other organisms. It is believed that they are the origins of green land plants.
2.5.1 Habitat
Algae can be found growing in aquatic and terrestrial environments. Majority are aquatic, fresh, brackish
and marine waters. Aquatic algae may be attached to rock, wood, or other aquatic vegetation or may be
free-floating. Attached algae in marine habitats often exhibit orderly zonation in the exposure of their
substrates at low tides. In contrast, other attached algae, like the kelps are usually sublittoral. A vast array
of unicellular, colonial and delicate filamentous algae are permanently suspended in water where they
may be associated with bacteria, fungi, protozoa and other marine animals to form a community known as
the planktonic algae, under favorable conditions may multiply rapidly and become strikingly abundant as
water blooms of which ‘red tides’ are an example. Some also show symbiotic relationship with other
organisms eg. lichen is a symbiotic relationship between algae and fungi.

Algae exhibit great diversity in size. They could be single cells as small as 1 m to large seaweeds which
may grow to over 50 m. A great deal of variation exists in the morphology of the algal body. Unicellular
algae have thallus like body and come in a variety of shapes – spherical, rod-like, spindle-like or club-
shaped eg. Chlamydomonas, diatoms etc. Multicellular algae may have leaf-like, root-like or stem-like
structures and occur in various other forms like filaments and branches eg. Fucus, Spirogyra. Some are
colonial eg. Volvox.
Algae are covered with a cell wall. An eukaryotic algae is characterized by the presence of a well-
organized nucleus and membrane bound organelles like plastids and membrane bound organelles like
plastids, mitochondria and Golgi bodies. Apart from possessing chlorophyll, they have various other
pigments that impart them with color red, brown and green. Some algae are either themselves motile or
move by means of certain motile cells which bear flagella. Two or more flagella are commonly inserted
anteriorly. Usually one flagellum is better developed than the other; the second may even be vestigial.
2.5.4 Reproduction
Asexual modes of reproduction involve fission, fragmentation and spore formation. Algae also reproduce
sexually.
2.5.6 Effects of algae
Useful effects: Humans use algae as food, for production of useful compounds, as biofilters to remove
nutrients and other pollutants from wastewaters, to assay water quality, as indicators of environmental
change, in space technology, and as laboratory research systems. Algae is commercially cultivated for
pharmaceuticals, nutraceuticals, cosmetics and aquaculture purpose. Algae can be used to make biodiesel
and vegetable oils. It can be grown to produce biomass, which can be burned to produce heat and
electricity. It has an abundance of vitamins, minerals, and proteins. It enriches water with oxygen as a
result of photosynthesis. Algae bioreactors are used by some power plants to reduce CO2 emissions.
Sewage are treated with algae, reducing the use of large amounts of toxic chemicals.
Harmful effects: In water reservoirs, sufficient nutrient availability results in luxuriant growth of algae
that float on water surface in masses and look like foam or soap lather. These algal masses are called
algal bloom. It causes oxygen depletion in the water of reservoirs thus causing death of aquatic animals
present there. Some of the bloom also produces toxins which sometimes prove fatal to the aquatic as well
as domestic animals consuming that water. Thus they pollute water and lead to eutrophication.
LICHENS
Lichens are examples of a symbiotic association involving a fungus and green algae. The fungus obtains
carbohydrates produced by photosynthesis from the algae or cyanobacteria, and in return provides its
partner(s) with protection from desiccation and ultraviolet light. Lichens grow in a wide range of habitats
on nearly every continent. Think about an inhospitable place, and there's probably a lichen that grows
there—on bare rocks, sidewalks, grave stones, the exoskeletons of some insects, and even on cars that
remain for a long time in one place.

2.6 VIRUS
Viruses are named from the Latin for poison (venenum). They are the smallest and simplest of replicative
agents of infection in humans. They are both the commonest organisms found in nature and the most
frequent cause of human infection. They can infect animals, plants, and even other microorganisms.
Viruses that infect only bacteria are called bacteriophages and those that infect only fungi are termed
mycophages. There are even some viruses called virophages that infect other viruses. Study of virus is
called virology.
Viruses are very small and they measured in nanometers. They can only be seen with an electron
microscope. They are composed of a core of DNA or RNA surrounded by a protein coat they can only
reproduce by infecting living cells. Their size ranges from 20 nanometers to 250 nanometers.
Shapes of viruses are predominantly of two kinds: rods, or filaments, so called because of the linear array
of the nucleic acid and the protein subunits; and spheres, which are actually 20-sided (icosahedral)
polygons. Most plant viruses are small and are either filaments or polygons, as are many bacterial viruses.
The larger and more-complex bacteriophages, however, contain as their genetic information double-
stranded DNA and combine both filamentous and polygonal shapes.
2.6.2 Distinguishing features
The following properties distinguish them from living (prokaryotic and eukaryotic) cells:
 They are acellular and have a simple organization i.e. they contain no cytoplasm or cellular organelles.
 They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery
i.e. viruses don't grow and divide. Instead, new viral components are synthesized and assembled within
the infected host cell.
 The vast majority of viruses possess either DNA or RNA but not both.
 They don’t respire.
 They can be crystallized and stored for a very long time.
Viruses can exist extracellularly, as virions (15–400 nm in diameter). They are considered both as living
and non-living things, as viruses are inactive when they are present outside of host cells and are active
inside of host cells. As they make use of raw materials and enzymes of the host cell to reproduce and
cause several infections.
2.6.3 Effects of viruses
Useful effects: They are useful in delivering genes to target cells and play a vital role in and gene therapy
researches.
Harmful effects: There are many pathogenic viruses, which causes harm to human beings, plants and
animals. In human beings, the diseases caused by viruses are: HIV, influenza, herpes, hepatitis, small pox,
polio, rabies, measles, etc. The diseases caused by viruses in plants are tobacco mosaic viruses, tomato
leaf curl, etc. The diseases caused in animals are foot and mouth disease, swine pox, Japanese b-
encephalitis, etc.

2.7 FOOD PRESERVATION
Food preservation is the process of treating and handling food to stop or slow down food spoilage, loss of
quality, edibility, or nutritional value and thus allow for longer food storage. Preservation usually
involves preventing the growth of bacteria, fungi (such as yeasts), and other microorganisms, as well as
retarding the oxidation of fats which cause rancidity.
Methods of Food Preservation
A number of methods of prevention can be used that can either totally prevent, delay, or otherwise reduce
food spoilage. Preservatives can expand the shelf life of food and can lengthen the time long enough for it
to be harvested, processed, sold, and kept in the consumer’s home for a reasonable length of time.
Maintaining or creating nutritional value, texture and flavor is an important aspect of food preservation,
although, historically, some methods drastically altered the character of the food being preserved. In
many cases these changes have now come to be seen as desirable qualities, as with cheese, yogurt, and
pickled onions.
 Drying is one of the most ancient food preservation techniques, which reduces water activity
sufficiently to prevent bacterial growth.
 Pasteurization of milk involves heating it to around 70C and then cooling it quickly. This kills most
bacteria without affecting the flavor.
 Refrigeration preserves food by slowing down the growth and reproduction of microorganisms and the
action of enzymes which cause food to rot.
 Freezing is also one of the most commonly used processes for preserving a very wide range of food
including prepared foodstuffs which would not have required freezing in their unprepared state.
 Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The
vacuum environment strips bacteria of oxygen needed for survival, thereby slowing spoiling. Vacuum-
packing is commonly used for storing nuts to reduce the loss of flavor from oxidation.
 Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or
sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute
to the characteristic pink color, as well as inhibition of Clostridium botulinum.
 Sugar is used to preserve fruits, either in syrup with fruit such as apples, pears, peaches, apricots,
plums, or in crystallized form where the preserved material is cooked in sugar to the point of
crystallization and the resultant product is then stored dry. This method is used for the skins of citrus
fruit (candied peel), angelica, and ginger. The use of sugar is often combined with alcohol for
preservation of luxury products such as fruit in brandy or other spirits. These should not be confused
with fruit flavored spirits such as cherry brandy.
 Smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing
the food to smoke from burning plant materials such as wood. Most commonly subjected to this method
of food preservation are meats and fish that have undergone curing. Fruits and vegetables like paprika,
cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but
mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably
arose after the development of cooking with fire.
 Preservative food additives can be antimicrobial. These inhibit the growth of bacteria or fungi,
including mold, or antioxidant, such as oxygen absorbers, which inhibit the oxidation of food
constituents. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium
nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.), and disodium EDTA.

Antioxidants include BHA and BHT. Other preservatives include formaldehyde (usually in solution),
glutaraldehyde (kills insects), ethanol, and methylchloroisothiazolinone.
 Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly
categorized into two categories: chemical pickling and fermentation pickling.
 Canning involves cooking food, sealing it in sterile cans or jars, and boiling the containers to kill or
weaken any remaining bacteria as a form of sterilization. Foods have varying degrees of natural
protection against spoilage and may require that the final step occur in a pressure cooker. High-acid
fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal
fruits such as tomatoes require longer boiling and addition of other acidic elements. Low acid foods,
such as vegetables and meats require pressure canning. Food preserved by canning or bottling is at
immediate risk of spoilage once the can or bottle has been opened.
Other forms of preservation can include: jellying, jugging, irradiation, pulsed electric field processing,
modified atmosphere, high pressure, burial in the ground, and biopreservation.
2.8 NITROGEN CYCLE
The nitrogen cycle describes the conversion of nitrogen between different chemical forms. The majority
of the earth’s atmosphere (about 78%) is composed of atmospheric nitrogen, but it is not in a form that is
usable to living things. Complex species interactions allow organisms to convert nitrogen to usable forms
and exchange it between themselves. Nitrogen is essential for the formation of amino acids and
nucleotides. It is essential for all living things.
Fixation: In order for organisms to use atmospheric nitrogen (N2), it must be “fixed” or converted into
ammonia (NH3). This can happen occasionally through a lightning strike, but the bulk of nitrogen fixation
is done by free living or symbiotic bacteria. These bacteria have the nitrogenase enzyme that combines
gaseous nitrogen with hydrogen to produce ammonia. It is then further converted by the bacteria to make
their own organic compounds. Some nitrogen fixing bacteria, Rhizobium live in the root nodules of
legumes where they produce ammonia in exchange for sugars. Today, about 30% of the total fixed
nitrogen is manufactured in chemical plants for fertilizer.
Nitrification: Nitrification is the conversion of ammonia (NH3) to nitrate (NO3
–
). It is usually performed
by soil living bacteria, such as nitrobacter. This is important because plants can assimilate nitrate into
their tissues, and they rely on bacteria to convert it from ammonia to a usable form. Nitrification is
performed mainly by the genus of bacteria, Nitrobacter.
Ammonification /Mineralization: In ammonification, bacteria (Bacillus vulgaris) or fungi
(Actinomyces) convert the organic nitrogen from dead organisms back into ammonium (NH4
+
).
Nitrification can also work on ammonium. It can either be cycled back into a plant usable form through
nitrification or returned to the atmosphere through de-nitrification.
De-nitrification: Nitrogen in its nitrate form (NO3
–
) is converted back into atmospheric nitrogen gas (N2)
by bacterial species such as Pseudomonas and Clostridium, usually in anaerobic conditions. These
bacteria use nitrate as an electron acceptor instead of oxygen during respiration.

The role of soil bacteria in the Nitrogen cycle: Nitrogen transitions between various biologically useful forms.

Solved Examples
Example 1
What are vaccines?
Solution
A vaccine is an inactivated form of bacteria or virus that is injected into the body to simulate an actual
infection. Because the injected microorganisms are 'dead,' they don't cause a person to become sick.
Instead, vaccines stimulate an immune response by the body by creating antibodies that will fight off
that type of illness. These antibodies act against the antigens and neutralize their toxins or destroy them.
Example 2
Fungus and bacterial infections do not occur in jams and pickles. Why?
Solution
The high sugar content, high osmotic pressure, low moisture and low water activity in the jams and
jellies prevent the growth of bacteria and fungi. The solutes (sugars, pectins, binders, etc.) used in the
manufacture of jam and jellies ties-up the available water and minimizes the growth of bacteria and
fungi that require a high water environment for proliferation and growth. Also, the employment of high
acidity (benzoates, citric acid, etc.), high temperature during processing, hermetic sealing during canning
and bottling of the jars/containers, and natural & artificial preservatives, further set-up microbial hurdles
that prevent growth of vegetative cells and inhibit sporulation (growth of microbial spores).
Example 3
What food items are prepared by using yeast?
Solution
Bread, beer and wine, idle and dosa are prepared by using yeast.
Example 4
Write the economic importance of bacteria in medicine.
Solution
Bacteria are responsible for preparation of sera and vaccine. These also produce streptomycin,
chloramphenicol, tetracycline and many others.
Example 5
How do microbes survive in adverse environmental condition?
Solution
Microbes can survive extreme conditions of temperature and dryness by forming a hard protective
covering or cyst through a process called encystment.
Example 6
Where do mosquitos breed?
Solution
Mosquitoes breed in stagnant water and damp places, etc.
Example 7
What are the basic features of protozoa?
Solution
These are single celled animals or in the form of small clusters of cells or colonies. They live in ponds,

rivers, lakes, and seas. Some are parasites in animals and human beings.
Example 8
What types of diseases can be prevented by vaccine?
Solution
Cholera, tuberculosis, small pox, hepatitis and polio can be prevented by vaccination.
Example 9
What are antibiotics?
Solution
Medicines used to kill or stop the growth of disease causing microorganisms inside human body are
called antibiotics.
Example 10
Who converts the various compounds of nitrogen present in dead animals and plants back into
nitrites and nitrates?
Solution
Conversion of nitrogenous organic compounds present in dead bodies into nitrites and nitrates is done by
decay causing organisms i.e. bacteria and fungi eg. Bacillus vulgaris, Nitrosomonas and Nitrobacter.
Example 11
What do you mean by pasteurization of milk? How does it differ from homogenization?
Solution
Pasteurization is a process that kills harmful bacteria by heating milk to a specific temperature for a set
period of time. First developed by Louis Pasteur in 1864, pasteurization kills harmful organisms
responsible for diseases like listeriosis, typhoid fever, tuberculosis, diphtheria, and brucellosis. The UK
Dairy Products Hygiene Regulations 1995 requires that milk be heat treated for 15 seconds at 71.7C or
other effective time/temperature combination. A process similar to pasteurization is thermization which
uses lower temperatures to kill bacteria in milk. In contrast, homogenization is the process of passing
milk under high pressure through thin tubes which reduces the tendency of creaming of fats.
Example 12
Give two examples from daily life about the beneficial effects of microorganisms.
Solution
Formation of curd through bacteria and preparation of various food dishes using mushroom.
Example 13
How does amoeba actually intake food?
Solution
Amoeba eats tiny microscopic plants and animals as food that floats in water in which it lives. When an
amoeba encounters a suitable organism, it pushes out two pseudopodia around the organism. Gradually,
the tips of the pseudopodia fuse with each other. As a result, the food is engulfed with a little
surrounding water to form a food vacuole.
Example 14
Can microorganisms be seen with the naked eye? If not, how can they be seen?
Solution
Microorganisms are too small. So they can’t be seen with naked eye. We have to use a microscope to

view microorganisms like bacteria and protozoa. Fungus that grows on the bread can be seen with a
magnifying glass.
Example 15
Name the microorganisms which can fix nitrogen in the soil.
Solution
Nitrogen is needed by the plants for their growth. They cannot absorb nitrogen directly from the air.
There are microorganisms like some bacteria and blue-green algae in the soil that take nitrogen from the
air and make nitrogenous compounds. Thus they enrich the soil with nitrogenous compounds and make
it fertile. These bacteria and blue-green algae are called biological nitrogen fixers.
Example 16
Explain the role of mosquitoes in spreading the diseases? How can we control them?
Solution
Mosquitoes act as carriers of many disease causing microorganisms. Anopheles mosquito carries the
parasite of malaria. Female Aedes mosquito carries the dengue virus from infected to the healthy person.
The spread of diseases can be controlled by killing the mosquitoes. The breeding places of mosquitoes
like water in the coolers, tyres, flowerpots, etc. should be drained out. Mosquito nets should be used at
night.
Example 17
Sneha wonders how food can become a ‘poison’?
Solution
Some microorganisms can spoil the food when they grow on it. Spoiled food emits bad smell and has a
bad taste and changed color. A toxic substance is produced in the food by these microbes. These make
the food poisonous. Consuming such food can cause food poison and serious illness and even death can
occur.
******

EXERCISE
 Multiple choice questions with one correct answer
1. Viruses are made of
(A) lipoprotein (B) glycosides (C) nucleoprotein (D) lipid
2. Which of the following produces antibiotics?
(A) Mucor (B) Rhizopus (C) Penicillium (D) Agaricus
3. Mushrooms are
(A) algae (B) fungi (C) bacteria (D) none of these
4. When yeast is added to grape juice and left for a week, the process is termed as
(A) fermentation (B) decomposition (C) distillation (D) oxidation
5. At 37C and in damp conditions, bacteria reproduce easily through
(A) binary fission (B) conjugation (C) budding (D) spore formation
6. Cholera is caused by
(A) Streptococcus (B) Clostridium (C) Pasteurella (D) Vibrio
7. Algae are autotrophs because they
(A) carry out anaerobic
respiration
(B) can manufacture
their own food
(C) feed on dead
organisms
(D) feed on other living
organisms
8. How oil spray on stagnant water controls malaria?
(A) kills malarial parasite in mosquitoes
(B) water becomes too dirty for mosquitoes
(C) mosquito larva can’t breathe
(D) none of these
9. Tuberculosis spreads by
(A) mosquito (B) houseflies (C) contaminated water (D) droplets of sneeze
and cough
10. Bread mould is the common name of
(A) Batrachospermum (B) Rhizopus (C) Agaricus (D) Fusarium
11. Ringworms can be prevented by
(A) vaccination (B) vector control (C) improving personal
hygiene
(D) using antibiotics
12. Microorganisms are used in genetic engineering for
I. The production of bioplastic
II. The production of hormones
III. Gene therapy

(A) II only (B) II and III (C) I and III (D) I, II and III
13. It is caused by a protozoan which causes fever and also cause anemia. The above information describes
the disease named
(A) Cholera (B) Malaria (C) Filariasis (D) Hepatitis B
14. Aedes and Anopheles are
(A) bacteria (B) protozoa (C) algae (D) none of these
15. The gas released during the preparation of bread is
(A) oxygen (B) carbon dioxide (C) nitrogen (D) sulphur dioxide
16. Pathogenic micro-organisms present in host cells are killed by medicines called
(A) pain killer (B) antibodies (C) antibiotics (D) vaccines
17. The two micro-organisms which live in symbiotic association in lichens are
(A) fungus, protozoa (B) alga, bacteria (C) bacteria, protozoa (D) alga, fungus
18. Ruhi dug two pits, A and B, in her garden. In pit A, she put a polythene bag packed with some
agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene
bag. She, then covered both the pits with soil. What did she observe after a month?
(A) Waste in pit A degraded faster than that in pit B.
(B) Waste in pit B degraded faster than that in pit A.
(C) Waste in both pits degraded almost equally.
(D) Waste in both pits did not degrade at all.
 Fill in the blanks
19. In size, viruses are ___________ than bacteria.
20. Bacterial virus is called _______________.
21. Viruses multiply only in living host suggest that they are _____________.
22. _______________ causes sleeping sickness.
23. Penicillin was discovered by ___________.
24. Production of antibiotics involves the use of ____________.
25. ____________ and ___________ are carried by mosquito.
 True or False
26. AIDS is a bacterial disease.
27. Malaria is caused by protozoa.
28. Double stranded DNA is found in tumour virus.
29. Fungi contain capsid.
30. Viruses are smallest microorganisms.

31. Virus multiplies in dead tissue.
32. Vaccines are produced by algae.
 Solve the following
33. Describe the cellular structure of a virus. How is it different from that of bacteria?
34. Write short notes on-
(i) nitrogen-fixing bacteria
(ii) blue-green algae
(iii) harmful effects of algae
(iv) prevention of growth of moulds
35. How do microorganisms enter into our body?
36. In which group multicellular microbes are present?
37. Write the diseases caused by protozoans. Explain them in details.
38. What are fungi? How do they affect us? Explain with figure.
39. Name the process in yeast that converts sugars into alcohol.
40. Suggest a suitable word for each of the following statements.
(a) Chemicals added to food to prevent growth of microorganisms.
(b) Nitrogen-fixing microorganism present in the root nodules of legumes.
(c) Agent which spreads pathogens from one place to another.
(d) Chemicals which kill or stop the growth of pathogens.
41. Observe the figure and answer the following questions.
(a) Name the microorganism and the group to which it belongs.
(b) Name the food item on which the organism grows.
(c) Does it grow well in dry or in moist conditions?
(d) Is it safe to eat infected bread?
42. How curdling of milk occurs?
43. How do vaccines work?
44. Name one commercial use of yeast.
45. Fungus infection doesn’t occur in jams and pickles. Why?

46. Match the following.
Column 1
(a) Lactobacillus
(b) Aspergillus
(c) Spirogyra
(d) Paramecium
Column 2
(i) Algae
(ii) Protozoa
(iii) Fungi
(iv) Bacteria
47. What are antibiotics? How are they produced?
48. Give reasons for the following.
(a) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed
without boiling.
(b) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside.
(c) Farmers prefer to grow beans and peas in nitrogen deficient soils.
(d) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water.
Why?
49. In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?
50. How is bread formed in industries?
51. How viruses replicate themselves?
52. Classify the following into friendly and harmful microorganisms.
Yeast, malarial parasite, Lactobacillus, bread mould, Rhizobium, Bacillus anthracis
53. Observe the set up given in fig below and answer the following questions.
(a) What happens to the sugar solution in A?
(b) Which gas is released in A?
(c) What changes will you observe in B when the released gas passes through it?
54. What do you mean by communicable diseases?
55. What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left in the open for a day or two?
56. What do you mean by fermentation? Differentiate between fermentation and pasteurization.
57. Match the following.

Column 1
(a) Louis Pasteur
(b) Robert Koch
(c) Edward Jenner
(d) Alexander Fleming
Column 2
(i) Penicillin
(ii) Anthrax bacterium
(iii) Fermentation
(iv) Small pox vaccine
58. Polio drops are not given to children suffering from diarrhoea. Why?
59. How can we prevent the following diseases?
(a) Cholera
(b) Typhoid
(c) Hepatitis A
60. While returning from the school, Raman ate chaat from a street hawker. When he reached home, he felt
ill and complained of stomach ache and fell ill. What could be the reason?
61. Why should we avoid standing close to a tuberculosis patient while he/she is coughing?
62. Define homogenization.
63. Unscramble the jumbled words underlined in the following statements.
(a) Cells of our body produce santiidobe to fight pathogens.
(b) curbossulite is an air-borne disease caused by a bacterium.
(c) Xanrhat is a dangerous bacterial disease.
(d) Yeasts are used in the wine industry because of their property of meronettinaf.
64. What are food preservatives? Mention some important ones.
65. What are the types of reproduction in fungi?
66. (a) Name two diseases that are caused by virus.
(b) Write one important characteristic of virus.
67. Describe food poising in details.
68. What is the importance of lichens?
69. Explain nitrogen cycle with a diagram.
70. Meera watched her grandmother making mango pickle. After she bottled the pickle, her grandmother
poured oil on top of the pickle before closing the lid. Meera wanted to know why oil was poured. Can
you help her understand why?
******

Answers
1. (C) 2. (C) 3. (B) 4. (A) 5. (A) 6. (D)
7. (B) 8. (C) 9. (D) 10. (B) 11. (C) 12. (B)
13. (B) 14. (D) 15. (B) 16. (C) 17. (D) 18. (B)
19. smaller 20. bacteriophage 21. living 22. T. brucei 23. Alexander Fleming
24. microorganisms 25. Dengue fever, malaria
26. False 27. True 28. True 29. False 30. True
31. False 32. False
36. algae, fungi 39. Fermentation
40. (a) Preservatives
(b) Rhizobium,
(c) Carrier/vector
(d) Antibiotics
41. (a) Bread mould. It is a fungus.
(b) Moist and stale bread.
(c) It grows well in moist conditions.
(d) No.
46. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii) 49. Nitrogen
52. Friendly - Yeast, Lactobacillus, Rhizobium
Unfriendly - malarial parasite, bread mould, Bacillus anthracis
53. (a) Yeast causes fermentation converting sugar into alcohol and carbon dioxide.
(b) Carbon dioxide
(c) Lime water turns milky
57. (a)-(iii); (b) (ii); (c)-(iv); (d)-(i) 63. (a) antibodies, (b) tuberculosis, (c) Anthrax,
(d) fermentation
66. (a) Polio/Chicken Pox/Influenza
******

Additional Notes for Competitive Exams
STRUCTURE OF VIRUS
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers
the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid
envelope. The entire intact virus is called the virion. The structure and composition of these components can
vary widely.
Viral genomes: While the genomes of all known cells are comprised of double stranded DNA, the genomes of
viruses can be comprised of single or double stranded DNA or RNA. They can vary greatly in size, from
approximately 5-10 kb (Papovaviridae, Parvoviridae, etc.) to greater than 100-200 kb (Herpesviridae,
Poxviridae). The known structures of viral genomes are summarized below.
DNA: Double Stranded - linear or circular
Single Stranded - linear or circular
Other Structures - gapped circles
RNA: Double Stranded – linear
Single Stranded - linear
The genome of some RNA viruses is segmented, meaning that a virus particle contains several different
molecules of RNA, like different chromosomes.
Protein capsid: Viral genomes are surrounded by protein shells known as capsids. One interesting question is
how capsid proteins recognize viral, but not cellular RNA or DNA. The answer is that there is often some type
of "packaging" signal (sequence) on the viral genome that is recognized by the capsid proteins. A capsid is
almost always made up of repeating structural subunits that are arranged in one or two symmetrical structures, a
helix or an icosahedron. In the simplest case, these "subunits" consist of a single polypeptide. In many cases,
however, these structural subunits (also called protomers) are made up of several polypeptides. Both helical and
icosahedral structures are described in more detail below.
Helical capsids: The first and best studied example is the plant tobacco mosaic virus (TMV), which contains a
single stranded RNA genome and a protein coat made up of a single, 17.5 kd protein. This protein is arranged in
a helix around the viral RNA, with 3 nt of RNA fitting into a groove in each subunit. Helical capsids can also be
more complex, and involve more than one protein subunit. Several families of animal virus contain helical
nucleocapsids, including the Orthomyxoviridae (influenza), the Paramyxoviridae (bovine respiratory syncytial
virus), and the Rhabdoviridae (rabies). All of these are enveloped viruses.
Icosahedral capsids: In these structures, the subunits are arranged in the form of a hollow, quasi spherical
structure, with the genome within. An icosahedron is defined as being made up of 20 equilateral triangular faces
arranged around the surface of a sphere. They display 2-3-5 fold symmetry as follows:
 an axis of 2 fold rotational symmetry through the center of each edge.
 an axis of 3 fold rotational symmetry through the center of each face.
 an axis of 5 fold rotational symmetry through the center of each corner.
These corners are also called vertices, and each icosahedron has 12. Since proteins are not equilateral triangles,
each face of an icosahedron contains more than one protein subunit. The simplest icosahedron is made by using
3 identical subunits to form each face, so the minimum number of subunits is 60 (20 x 3). Remember, that each
of these subunits could be a single protein or, more likely, a complex of several polypeptides.

Many viruses have too large a genome to be packaged inside an icosahedron made up of only 60 polypeptides
(or even 60 subunits), so many are more complicated. In these cases, each of the 20 triangular faces is divided
into smaller triangles; and each of these smaller triangles is defined by 3 subunits. However, the total number of
subunits is always a multiple of 60. The total number of subunits can be defined as 60  N, where N is
sometimes called the triangulation number, or T. Values for T of 1,3,4,7,9, 12 and more are permitted.
When virus nucleocapsids are observed in the electron microscope, one often sees apparent "lumps" or clusters
on the surface of the particle. These are usually protein subunits clustered around an axis of symmetry, and have
been called "morphological units" or capsomers.
Viral envelope: In some animal viruses, the nucleocapsid is surrounded by a membrane, also called an
envelope. This envelope is made up of a lipid bilayer, and is comprised of host-cell lipids. It also contains
virally encoded proteins, often glycoproteins which are trans-membrane proteins. These viral proteins serve
many purposes, such as binding to receptors on the host cell, playing a role in membrane fusion and cell entry,
etc. They can also form channels in the viral membrane.
Many enveloped viruses also contain matrix proteins, which are internal proteins that link the nucleocapsid to
the envelope. They are very abundant (i.e. many copies per virion), and are usually not glycosylated. Some
virions also contain other, non-structural proteins that are used in the viral life cycle. Examples of this are
replicases, transcription factors, etc. These non-structural proteins are present in low amounts in the virion.
Enveloped viruses are formed by budding through cellular membranes, usually the plasma membrane but
sometimes an internal membrane such as the ER, golgi, or nucleus. In these cases, the assembly of viral
components (genome, capsid, matrix) occurs on the inside face of the membrane, the envelope glycoproteins
cluster in that region of the membrane, and the virus buds out. This ability to bud allows the virus to exit the
host cell without lysing, or killing the host. In contrast, non-enveloped viruses, and some enveloped viruses, kill
the host cell in order to escape.
******

Worksheet 1
1. Based on the characteristics given, identify the type of microbe.
(a) Autotrophic and are present as scum on the water bodies.
(b) These are killed by antibiotics.
(c) These are saprophytic.
(d) These are difficult to classify as living or non-living.
2. State the role of the following pathogen in our life.
(a) Bacteria
(b) Yeast
(c) Algae
(d) Protozoa
(e) Virus
3. Mention.
(a) Any three antibiotics.
(b) Algae rich in proteins and other nutrients.
(c) Bacteria that helps in nitrogen fixation.
(d) Microorganism used to make cheese.

Worksheet 2
1. Name the microorganism that is responsible for these diseases.
(a) Polio
(b) Typhoid
(c) Citrus canker
(d) Septoria leaf blotch
(e) Apple scab
(f) Fin rot
(g) Anthrax
(h) Dengue
2. Name the microorganism that is responsible for these diseases.
(a) Boiling
(b) Using sugar
(c) Canning
(d) Pasteurization
(e) Dehydration
(f) Freezing
(g) Using salt
(h) Using chemical preservatives
(i) Using vinegar

Answers
Worksheet 1
1. (a) Algae (b) Microorganisms (c) Fungi (d) Virus
2. (a) Lactobacillus bacteria is used to make curd.
(b) Yeast is used to make bread.
(c) Diatoms are used to make toothpaste.
(d) Malaria disease is caused by Plasmodium protozoa.
(e) Measles, chicken pox and dengue are caused by virus.
3. (a) Penicillin, Tetracycline, Streptomycin
(b) Chlorella
(c) Rhizobium
(d) Lactobacillus bacteria
Worksheet 2
1. (a) Virus (b) Bacteria (c) Bacteria (d) Fungi (e) Fungi (f) Bacteria/ Fungi (g) Bacteria (h) Virus
2. (a) Milk (b) Jam (c) Fish (d) Milk (e) Cereals (f) Fruits (g) Meat (h) Squashes (i) Vegetables
******

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