Monos means single, it includes all prokaryotic organisms (mycoplasma, bacteria, actinomycetes and photosynthetic cyanobacteria).
The characteristics of Monera are:
- Unicellular, mycelial, filamentous or colonial.
- On the basis of shape bacteria are divided into
Coccus - micro coccus (mono), diplodocus (in pairs), streptococcus (in chains), staphylococcus (in clusters).
Bacilli - rod shaped
Spirilla - spiral or twisted in shape
Vibrio – comma shaped.
- Small, microscopic .1 to few microns in length.
- Prokaryotic in nature.
- A slimy layer called capsule surrounds the cell wall.
- May be motile or nonmotile. By means of simple flagella (flagellin protein) they are able to swim or glide.
- Single cell envelope system. Most of them bear rigid cell wall consists of peptidoglycan instead of cellulose (except mycoplasma).
- Cell contain plastid, mitochondria, endoplasmic reticulum, golgibody, lysosome and other membrane bound organelles are absent
- Genetic material is naked circular DNA (neither enclosed nor combined with complex protein)
- Not a single well defined chromosome is present (nucleoid)
- It’s DNA content is called prochromosome or chromosome.
- Ribosomes are 70s and arranged in polysomes.
- Nutrition of bacteria is saprophytic and parasitic in nature.
- Reproduction is primarily asexual (budding, binary fission) or paradoxical gene recombination in some cases. In unfavourable condition, they reproduce by binary fission- the circular DNA elongates and divides, followed by a transverse constriction that appears in the middle. Then wall is formed through the middle of the cell to produce two daughter cells.
Under unfavorable condition bacteria can reproduce by spore formation. Protoplasm of the cell form a spherical mass and secrets a thick impervious wall around it. When it gets favorable condition, it breaks the cell and comes out.
Their modes of nutrition are absorptive, chemosynthetic, and photosynthetic. Photosynthetic may be oxygen in (cyanobacteria) and anoxygenic (bacteria).
Economic importance of bacteria are:
- Bacteria are the major sources of antibiotic.
- Antibiotics like
Streptomycin-Streptomyces griseus .
Tyrothricin- Bacillus brevis.
Polymyxin- Paenibacillus polymyxa.
- For vaccine preparation dead or weakened pathogens are used to develop antitoxin that provides immunity.
- In agriculture bacteria helps in the nitrogen fixation. It helps to grow plants as plants cannot take nitrogen directly from the environment for their growth. Rhizobium bacteria which are present in the root nodules of leguminous plant and convert free nitrogen into nitrate salt that absorb by the plant root with water.
- In industry fermentation by bacteria is used for curing tea leaves.
Harmful activities of bacteria are
1. Spoilage of food occurs by bacteria.
2. Citrus canker, wilt of tobacco etc are plant diseases caused by bacteria.
3. Animal diseases like cholera, typhoid etc occurs by bacteria.
1. What do you mean by nitrification?
The process of conversion of ammonia into nitrites and then into nitrate is called nitrification.
2. Name the bacteria causing cholera and typhoid.
Cholera is caused by Vibrio cholera, Typhoid is caused by Salmonella typhi.
3. Which bacteria cause crown gall of sugar beet?
4. Which bacteria cause food poisoning?
Clostridium botulinum is responsible for food poisoning.
5. What is pasteurization?
The process of heating milk at 60℃ for 30 minutes and then sudden cooling destroy germs is called pasteurization.
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