Download viruses, bacteria and cyanobacteria

VIRUSES, BACTERIA AND CYANOBACTERIA
Biology Class IX
7/13/2015
Educast
Lubna Naz
Chapter #4
VIRUSES, BACTERIA AND CYANOBACTERIA
Contents:
1. MICRO-ORGANISMS — AS A HETEROGENOUS GROUP OF
ORGANISMS
a. Viruses Characteristics
b. Viral diseases
c. Bacteria and its types
d. Importance of Bacteria
Objectives:
Learning objectives:
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Micro-organisms, a heterogenous group of living organisms which can only be seen with the
help of microscope.
Discovery of virus, characteristics, structure, types and the diseases caused by viruses in
humans, other animals and plants.
Characters of bacteria.
Shapes, nutrition and importance of bacteria.
Characters of cyanobacteria.
VIRUSES, BACTERIA AND CYANOBACTERIA
MICRO-ORGANISMS — AS A HETEROGENOUS GROUP OF ORGANISMS
Microorganisms are often illustrated using single-celled, or unicellular organisms; however,
some unicellular protists are visible to the naked eye, and some multicellular species are
microscopic.eg. bacteria, fungi, viruses
VIRUSES:
A virus is a small infectious agent that replicates only inside the living cells of other organisms.
Viruses can infect all types of life forms, from animals and plants to microorganisms,
including bacteria and archaea. The word is from the Latin virus referring to poison. By 1800's
many biologists had demonstrated that many diseases of man and other organisms were caused
by bacteria. Some diseases puzzled them. One such disease was tobacco mosaic disease
occurring in tobacco plant leaves. In 1892, Russian biologist, Iwanowsky showed that this
disease was due to something smaller than bacteria. He named them as viruses. No one had seen
them because they were too small to be seen even with the compound microscope.
The year 1935 was important in solving the story of what viruses really are and how they
behave. A new kind of microscope the electron microscope had been constructed and any object
smaller than mµ (millimicron 1,000,000,000th part of a metre) can be observed. Wendell Stanley
crystallized the infectious particles, now known as tobacco mosaic virus (TMV). This TMV and
many other viruses were actually seen with the help of the electron microscope.
CHARACTERISTICS:
The simple viruses use the enzymes of the host cell for both their protein synthesis and gene
replication; the more complex ones contain up to 200 genes and are capable of synthesizing,
through their host many structural proteins and enzymes themselves. Viruses are either virulent,
destroying the cell in which they occur or temperate, becoming integrated into their host
genomes (total hereditary materials) and remaining stable there for long periods of time.
Structure
Viruses display a wide diversity of shapes and sizes, called morphologies. In general, viruses are
much smaller than bacteria. Most viruses that have been studied have a diameter between 20 and
300 nanometers. Some filoviruses have a total length of up to 1400 nm; their diameters are only
about 80 nm. A complete virus particle, known as a virion, consists of nucleic acid surrounded
by a protective coat of protein called a capsid. These are formed from identical protein subunits
called capsomeres. Viruses can have a lipid "envelope" derived from the host cell membrane.
The capsid is made from proteins encoded by the viral genomeand its shape serves as the basis
for morphological distinction. They appear like small rods, tadpoles 6r may be polyhedrals or
like little spheres.
Viruses may consist of nucleic acid, capsids, envelopes and tail-fibers. Their nucleic acid may
consist of a single or several molecules of DNA or RNA. The smallest viruses have only four
genes while the largest have upto two hundreds. The protein coat that encloses the nucleic acid is
called a capsid. It may be of different shapes. Capsid is made up of protein subunits called
capsomeres. The number of capsomeres is characteristics of a particular virus.
Some viruses have accessory structures called viral-envelopes that help them infect their hosts.
They are membranes covering their capsids. The simplest viruses consist of a single molecule of
a nucleic acid (DNA or RNA) surrounded by a capsid, which is made up of different protein
molecules. Some bacterial viruses or bacteriophages, are among the most complex viruses. Each
of them is made up of at least five separate proteins: these make up the head; the tail core, the
molecules of the capsid, the base plate of the tail, and the tail fibers. A long DNA molecule is
coiled within the head.
They may be:
Plant-viruses infecting plants,
Animal-viruses infecting animals and
Bacteriophages which infect bacteria.
Viruses living or non-living:
Viruses with their core of DNA or RNA surrounded by a protein coat somewhat resemble the
chromosomes of other living organisms.
2. They have the ability to reproduce (Property of replication-reproduction).
3.
Many kinds of viruses are known to undergo mutations.
4.
Viruses show genetic recombination.
However, they show following characteristics not exhibited by living organisms.
i)
Non-cellular structure.
ii)
Undergo crystallization.
iii)
Completely inactive outside host's cell.
Viral diseases (Transmission/spread and control)
1.
Animal diseases:
Several of the animal viruses cause many important diseases. Poliomyelitis caused by polio virus
was a wide spread, crippling disease. Although poliomyelitis is now largely under control by
vaccination in the developed countries, it remains a serious and common disease in the tropics
and elsewhere in the less developed parts of the world. Colds are viral infections of the upper
respiratory tract. More than 200 of viruses that cause colds have been identified.
Measles and Mumps are the common viral diseases of children. However, proper vaccination of
MMR vaccine develops immunity against these infections. Human Immune Virus (HIV) was
discovered in 1985 to be the cause of Acquired Immune Deficiency Syndrome (AIDS).
Rabies, in humans is also caused by a virus but flu is the most common disease caused by the
influenza virus.
The majority of human viral diseases are spread through respiratory tract by air borne droplet
spread by sneezing and coughing of infectious people or by the contaminated water and food or
by blood or other body fluids. Hygienic living and vaccinations are the two best controls of viral
diseases.
2.
Plant diseases:
One of the best known plant diseases is caused by tobacco mosaic virus. This virus affects the
leaves of tobacco plants and light green and yellow patches appear on the leaves of diseased
plant. Agriculturists have not yet succeeded to device cure for most of viral diseases of plants.
Therefore, their efforts are focused largely on reducing the incidence and transmission of such
diseases and also on developing varieties of crop that are relatively resistant to certain viruses.
Bacteria
Bacteria are often maligned as the causes of human and animal disease (like this one, Leptospira,
which causes serious disease in livestock). However, certain bacteria, the actinomycetes, produce
antibiotics such as streptomycin and nocardicin; others live symbiotically in the guts of animals
(including humans) or elsewhere in their bodies, or on the roots of certain plants, converting
nitrogen into a usable form. Bacteria put the tang in yogurt and the sour in sourdough bread;
bacteria help to break down dead organic matter; bacteria make up the base of the food web in
many environments. Bacteria are of such immense importance because of their extreme
flexibility, capacity for rapid growth and reproduction, and great age - the oldest fossils known,
nearly 3.5 billion years old, are fossils of bacteria-like organisms.
Form (Shapes):
Perhaps the most elemental structural property of bacteria iscell morphology (shape). Typical
examples include:
 Coccus (spherical) (Singular-Coccus = Gr. Kokkos = Berry, rounded). They are
spherical and according to cell-arrangement they are: Solitary (single)
(Monococcus), in pair (Diplococci), in chain (Streptococci), in cluster
(Staphylococci) etc.They are non-flagellated.
 Bacillus (rod-like) (Singular-Bacillus = L, Bakulus = A rod) .They are rod shaped.
They may be found in pairs (Diplobacillus) or in chains (Streptobacillus)
etc. They may be flagellated.
 Spiral Spirilla: (Singular-Spirillum = Gr. Sperira = A coil. They are spiral or cork
screw shaped (spirillum).
 Vibrio or comma: They are slightly curved or comma (,) shaped e.g
Vibrio cholerae. They may be flagellated.
2 Nutrition:
Most bacteria are heterotrophic with few autotrophic. Heterotrophic bacteria are those which
cannot synthesize their organic compounds from simple inorganic substances. According to their
mode of feeding, heterotrophic bacteria may be saprophytic, symbiotic or parasitic.
i)
Saprophytic bacteria:
They get their food from dead organic matter. The soil is full of organic compounds in the form
of humus. Bacteria living in the soil have large number of enzymes that break down the complex
substances of humus to simpler compounds. These bacteria absorb and utilize these simple
compounds as a source of energy. Many other saprophytic bacteria cause decay of dead animal
and plant material as they convert complex organic compounds to simpler ones.
ii)
Symbiotic bacteria:
They are found associated with other living organisms. They obtain food from the host without
harming it, e.g. nitrogen fixing bacteria in the roots of leguminous plants.
iii)
Parasitic bacteria:
They grow inside the tissues of other living organisms and obtain food at the expense of host.
These bacteria lack certain complex systems of enzymes.
iv) Autotrophic bacteria:
They can synthesize organic compounds from simple inorganic substances. Autotrophic bacteria
may be photosynthetic or chemosynthetic.
a) Photosynthetic bacteria: They have pigments very similar to the chlorophyll and named as
bacterio chlorphyll. These pigments are bounded by invaginated plasma membrane in the
cytoplasm and not in the chloroplast. They carry out photosynthesis.
The majority of bacteria are free-living heterotrophs (saprophytic decomposers) that contribute
significantly to recycling matter through ecosystems. Many are also symbiotic heterotrophs,
including those that cause disease.
b) Chemosynthetic bacteria: They obtain their energy from oxidation of some inorganic
substances like iron, hydrogen, nitrogen and sulphur compounds to synthesize their organic
compounds.
Respiration:
Another aspect of metabolism which can be used in the classification of bacteria is their need for
oxygen in respiration.
Aerobes require oxygen for respiration.
Anaerobes respire without oxygen.
Some bacteria are killed in the presence of oxygen, they are called obligate anaerobes. Others
use oxygen but can respire without it, they are called facultative anaerobes. Bacteria which can
only survive with oxygen present are obligate aerobes.
Importance of bacteria:
1. Useful bacteria:
i) Agricultural bacteria: Bacteria decompose dead plants and animals bodies and convert various
organic compounds into simple forms such as nitrates, sulphates, phosphates etc for utilization
by green plants again. Nitrifying bacteria convert the proteins of these dead bodies into nitrates.
Then these nitrates are absorbed and utilized by the green plants. Soil bacteria increase the
fertility of the soil by bringing about physical and chemical changes in the soil.
ii) Alimentary canal bacteria: They help herbivores in the digestion of
Cellulose by producing an enzyme Cellulose.
Similarly some are present in human beings and make vitamins.
iii) Industrial bacteria: They help in curing and ripening of tobacco leaves, fermentation of
sugar into alcohol, ripening of cheese, retting (softening) of fibres, curdling of milk, conversion
of hides into leather etc.
iv) Medicinal bacteria: Valuable antibiotic drugs have been obtained from bacteria, e.g
Thyrothycin,
Subtilin. Riboflavin is a vitamin produced by Clostridium.
CYANOBACTERIA (Blue green algae)
Salient features of this group are:
1. These blue-green algae are Prokaryotic.
2. They may occur alone or in the form of colony.
3. Cell wall is double layered.
4. Protoplasm is differentiated into an outer coloured region—chromoplasm and an inner
colourless region—centroplasm.
5. Found in fresh water, few are marine.
6. Total absence of sexual reproduction.
7. Only asexual reproduction takes place e.g. Nostoc, Anabena. Cyanobacteria are
photosynthesizers that sometimes can also fix atmospheric nitrogen. They were probably the first
organisms who introduced oxygen into the primitive atmosphere and probably first to colonize
land.
NOSTOC:
Taxonomic position: According to new classification, Nostoc belongs to kingdom
prokaryotae(Monera).
Structure:
The Nostoc is filamentous. The filaments are intermixed in a gelatinous mass forming a ball like
structure. It floats on water. A single filament look like a chain of beads. Each filament is
unbranched and has a single row of rounded or oval cells. Each cell has double layered wall. The
outer thicker layer is made up of cellulose mixed up with pectin. The inner thin layer is made up
purely of cellulose.
The protoplasm is differentiated into an outer coloured region - chromoplasm and an inner
colourless region centroplasm.
There is total absence of endoplasmic reticulum, mitochondria, golgi bodies and vacuole.
However ribosomes, pseudovacuoles and reserve food are present.
The centroplasm also called central body have hereditary material (DNA) in the form of long
coiled structure called chromatin body.
At interval there are found slightly larger oblong, colourless cells with slightly thicker walls.
These are called heterocyst. Each heterocyst is the center of nitrogen fixation. But they are
specially concerned with the multiplication of filaments during unfavorable conditions.
IMPORTANT POINTS
called micro organisms. They form a heterogenous group which includes
viruses, bacteria, cyanobacteria, protozoa, unicellular algae and some fungi.
organisms.
-cellular parasites. They cannot live and reproduce outside the living cells.
bacteriophages are among the most complex viruses.
-viruses infecting plants. Animal-viruses infecting
animals. Bacteriophages are those which infect bacteria.
iety of shapes.
heterotrophic bacteria may be saprophytic, symbiotic or parasitic.
igate anaerobes. Others
use oxygen but can respire without it, they are called facultative anaerobes. Bacteria which need
oxygen for survival are obligate aerobes.
ants.
They may act as invisible enemies of man.
like structure. It floats on water. A single filament look like a chain of beads.