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Essay on Microorganisms | Microbiology

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❶Micro-organisms can thrive in any kind of environment.

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Microorganism Essay Writing Help. Buy Custom Made Essay Papers on Microorganism Microorganisms are the tiny organisms that cannot be seen by the naked eyes.

We have collected some information you can use for your microorganism essay: The nature- the basic approach for the essay could be dealing with the nature of the microorganisms.

You can talk about their size, how they look in the microscope, their habitat, how they function in different environment, where they are found, whether they are plants or animals, and similar other basic nature. In the ecosystem- what is the place of microorganisms in the ecosystem- can also be answered in the paper.

They help to decompose the dead and rotten plants and animals. Just imagine all the dead body and rotten plants staying around us! The microorganisms decompose them and mix them to the earth, creating chemicals that can be absorbed by the plants. The types- there are many different types of microorganisms.

You can divide it into unicellular and multicellular microorganisms and deal with the nature of each. Also there are bacteria, fungi, viruses, algae, yeasts, plankton- all of which come under microorganisms but have different features and characteristics and behavior. The history- microorganisms were the first living beings on the earth existing for about 4 billion years now. Though people were aware of some foreign body might be affecting the human beings with some diseases, the actual microorganisms was discovered in 17th century only.

Each end of crista is anchored in the cytoplasm. Spirochaetes are found in fresh, sea and polluted waters. They divide by binary fission and do not produce resting spores. Examples of spirochaetes are Cristispira, Treponema, Spirochaeta etc.

The study of the bacterial cell wall dates back to more than five decades when Salton and Home described the structure of cell wall for the first time; this was later confirmed by electron microscopic studies.

Cell wall is a dense layer surrounding the plasma membrane and functions to give shape and rigidity to the cell. Concentration of dissolved solutes inside a bacterial cell like that of E. This amount of pressure is counterbalanced by the cell wall. Bacteria can be divided into two major groups, namely, gram-positive and gram-negative on the basis of differences in their cell-wall structure.

The main constituent or back-bone of bacterial cell wall is peptidoglycan also known murein, muramic acid or mucopeptide which is biochemically unique and is absent in the cell walls of Archaea archaebacteria or any eukaryotc.

Though the peptidoglycan is present in both gram-positive and gram-negative bacteria cell walls, it alone does not make the whole structure of the complex cell wall and is accompanied with other biochemical components. Peptidoglycan, the main constituent or back-bone of bacterial cell wall, consists of two parts: The peptide portion is a short-chain composed of four amino acids L-alanine, D-glutamine, either L-lysine or diaminopimelic acid, and D-alanine connected with each other by piptide-linkages and hence is called tetrapeptide chain.

The two adjacent of different tetrapeptide chains are interlinked by a cross-linkage peptide interbridge. The type and extent of cross-linkages may vary among different species. In some species, the cross-linkage forms between the carboxyl group -CO- of an amino acid in one tetrapeptide chain and amino group -NH- of an amino acid in other tetrapeptide chain Fig.

In others, a pentaglycine chain is used to link two tetrapeptide side chains Fig. It is these cross-linkages that provide rigidity to the peptidoglycan which helps protecting the cell against osmotic socks exerted on it. However, the diaminopimelic acid DAP does not occur in the peptidoglycan of all bacteria; only all gram-negative bacteria and some gram-positive bacteria possess it. Most of the gram-positive bacteria have amino acid lysine instead of DAP. Another unusual feature of the peptidoglycan i.

It is because in proteins amino acids are always of L-configuration. The chemical structure of one of the repeating units of peptidoglycan is given in Fig. The cell wall of gram-positive bacteria Bacillus, Streptococcus, etc. The remainder being made up of proteins, polysaccharides, and teichoic acid.

Teichoic acids are acidic polysaccharides, which lie on the outer surface of the peptidoglycan, and are covalently bonded with it. Their functions are not known with certainty; they are considered to affect the passage of ions, thereby help maintain the cell wall at a relatively low pH so that self- produced enzymes autolysins do not degrade the cell wall.

Other functions are also attributed to teichoic acid such as binding metals and acting as receptor sites for some viruses. The wall of gram-negative bacteria Rhizobium, Escherichia, Salmonella, etc.

The region between the inner plasma membrane and the outer membrane is called periplasmic space. The outer membrane is present outside the thin peptidoglycan layer Fig. It is a small lipoprotein covalently joined to the underlying peptidoglycan and embedded in the outer membrane by its hydrophobic end. There are, however, a special type of porin proteins present in the outer membrane.

Three porin molecules cluster together and span the outer membrane to form a narrow channel through which molecules smaller than about daltons can pass. The most unusual constituents of the outer membrane are its lipopolysaccharides LPSs. The latter are large, complex molecules consisting of three parts: Lipid A is a major constituent of lipopolysaccharide and helps stabilize the outer membrane.

Lipid A often is toxic and functions as an endotoxin. The core polysaccharide usually contains charged sugars and phosphate and contributes to the negative charge on the bacterial surface. Besides peptidoglycan, there are teichoic acids, other polysaccharides and proteins in the cell wall.

Besides peptidoglycan, there are phospho-lipids, proteins and lipopolysaccharides in the cell wall. Teichoic acids are absent. Outer membrane serves as protective barrier. Despite its permeability to small molecules due to porin proteins, the outer membrane prevents or slows the entry of bile salts, antibiotics, lysozymes and other toxic substances which might kill or injure the bacterium.

As a result, infections with gram- negative bacteria are often more difficult to treat. Since teichoic acid is absent and the peptidoglycan is less in amount, the wall of gram-negative bacterium is less rigid as compared to that of gram-positive one. Bacteria vary in size from cells as small as 0. Bacteria are thus extremely small in comparison to eukaryotes. Small size of bacteria and almost all other prokaryotes affects a number of their biological properties.

For convenience, the rate at which the nutrients are taken in and wastes are passed out of a cell is in general inversely proportional to cell size. This is because transport rates are to some degree a function of the membrane surface area available; small cells have more surface area available than do large cells.

The parameters of rapid growth and larger cell populations greatly affect microbial ecology. It is so because high numbers of rapidly metabolizing cells can cause major physio-chemical changes in an ecosystem even over very short periods of time.

The pattern of flagellar arrangement flagellation is a good identification mark in bacteria Fig. Flagella are either confined to the pole or poles or it may be present all-round the body of the bacterium.

However, bacteria can be grouped as under on the basis of flagellation. Flagellar machinery of a bacterial prokaryotic cell has evolved responses to the gradients of physical and chemical agents in nature to which they often encounter.

These responses to gradients may be positive or negative by directing movements of the body either toward or away respectively. Such gradient-directed movements are called taxes sing, taxis. A variety of taxes are found taking place in bacteria depending upon which type of gradient governs the movement.

However, the different types of taxes behavioral responses are: When motile bacteria react to chemical stimuli, they accumulate in some areas or retreat from others. Such stimulus-response behaviour is called chemotaxis. The attraction of organisms by chemical stimuli is brought about in the following manner Fig.

Peritrichously flagellated bacteria e. The latter interrupts the straight movement and causes reorientation. If the bacteria are placed in a concentration gradient of an attractant, the linear swimming movement will last many seconds if it is in the direction of the optimal concentration of the attractant, but in the opposite direction it is interrupted after only a few seconds. Whilst the tumbling movement leads to a completely random selection of the new swimming direction, the direction- dependent duration of the linear swimming motion results in accumulation of the organisms in the region of optimal substrate concentration.

The sensing of, and response to, stimuli is due to specific chemosensors, the binding proteins present in the cell envelop. Bacteria possess a memory system that allows them to compare the concentrations of chemicals as they swim along, so that they effectively detect chemical concentrations over distances many times the length of a cell.

In some cases, these are independent of substrate assimilation. Thus, some mutants show unchanged chemotactic reactions to certain nutrients, though they have lost the capacity to utilise them. Many phototrophic microorganisms move towards light, a process called phototaxis. The phototrophic purple bacteria depend on light for their energy supply. Therefore, it is not surprising that they possess a phototactic mechanism and accumulate in illuminated areas.

The advantage of phototaxis is that it allows a phototrophic microbe to orient itself most efficiently for photosynthesis. If one projects a small spot of light onto a thick suspension of Chromatium on a slide previously kept in the dark, the organisms can be seen to collect in the illuminated area. Moreover, it appears that the organisms cannot leave the illuminated area, once they have entered it, in the course of their random movements. On entering the dark zone, abrupt reversal of flagellar motion propels them back into the light zone.

Even slight differences in light intensity between areas of illumination can evoke this reaction. Some Chromatium species accumulate in areas that receive only 0. This contrast sensitivity with regard to illumination is similar to that of the human eye 0. In some species, such as the highly motive phototrophic bacteria e. Rhodospirillum centenum , the entire colonies of cells show phototaxis and move in unison toward the light.

Bacterial movements towards or away from oxygen or air is called aerotaxis. Some motile bacteria reveal their metabolic capacities relative to oxygen or air by their aerotactic movements. When bacterial suspensions are placed between slide and coverslip, aerophilic bacteria accumulate near the edge of the coverslip and in the vicinity of air bubbles, demonstrating their requirement for aerobic conditions and their dependence on aerobic respiration for energy.

Strictly anaerobic bacteria, on the other hand, tend to collect in the centre, whilst microaerophilic bacteria, such as some pseudomonads and spirilla, keep a certain distance from the air interface. Some bacteria contain inclusion of iron granules called magnetosomes which permit them to orient their movement in response to magnetic fields. This phenomenon is called magnetotaxis.

A number of bacteria rods, spirilla, cocci has been isolated recently from the surface layers of sediments in freshwater ponds and the sea. These have been found to orientate themselves in a magnetic field and swim in the direction of the field lines.

They possess unusual amounts of iron 0. Magnetotactic behaviour thus enables these bacteria to migrate downwards into the oxygen-poor or oxygen-free sediments. Since the magnetotactic bacteria are anaerobic or microaerophilic, this mechanism and behaviour finds a ready ecological explanation. It indicates that the polarity is not genetically governed process.

Endospore-producing bacteria occur most commonly in the soil and the genera Bacillus and Clostridium are the best studied of endospore-producing bacteria. These spores are extraordinarily resistant to environmental stresses such as heat, ultraviolet radiation, gamma radiation, chemical disinfectants, and desiccation and can remain dormant for extremely long periods of time.

Endospores are of great practical significance in food, industrial and medical microbiology due to their resistance and dangerous pathogenic nature of several species of endospore- producing bacteria. This is because it is essential to develop adequate methods to sterilize solutions and solid objects.

The endospore so named because of its formation within the cell , which is readily seen under the light microscope as strongly refractile bodies Fig. The outermost layer is exosporium, a thin delicate covering made of protein. Beneath the exosporium, there is a thick spore-coat consisting of several protein layers which are spore- specific. Below the spore-coat is the cortex which may occupy as much as half the spore volume.

Cortex consists of loosely cross- linked peptidoglycan. Inside the cortex, there is the core-wall which surrounds the core membrane and the core or spore protoplast. The latter possesses cytoplasm, nucleoid, ribosomes etc. The core or spore protoplast of a mature endospore contains abundant dipicolinic acid and calcium ions normally existing in the form of calcium-dipicolinate complex Fig.

Because of it, the consistency of the core cytoplasm is that of a thick gel. In addition to low water content, the pH of the core cytoplasm is about one unit lower than that of the vegetative cell and contains high levels of core-specific proteins, namely, small acid- soluble spore proteins SASPs. A mature endospore differs greatly from the vegetative cell from which it was formed. These differences are given in Table 4.

Endospore formation called sporulation or sporogenesis involves a very complex series of events in cellular differentiation. Endospore formation takes place only in such a vegetative cell which ceases growth due to lack of nutrients.

Bacterial endospores can retain viability for many years. A few viable endospores of Bacillus subtilis and B. Endospores can even retain viability for millennia, and viable endospores have been found in geological deposits where they must have been dormant for thousands of years. What factors are responsible for such prolonged viability of endospores?

It has long been thought that dipicolinic acid was directly involved in heat-resistance of endospore, but heat- resistant mutants now have been isolated in which dipicolinic acid is absent. Then, if not DPA, what factors make endospore so resistant to heat and other lethal agents.


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Microorganisms play an important role in our life: helps us to digest our food, decompose wastes and participate in various cycles. They.

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Short Essay on Micro-Organisms. Article shared by. Soil contains a large number of bacteria and other microbes. Several microbes are harmful to us. They cause disease like cholera, typhoid, polio and leprosy in human beings. Some of these microbes are helpful to us. The nitrogen-fixing bacteria found in the root nodules of leguminous plants.

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Microorganisms, which include many different fungi, bacteria, and actinomycetes, are considered the architects of the soil as they have the ability to create a strong ecosystem in the soil. Microorganisms work best in communities to develop the structures for plants. ADVERTISEMENTS: In this essay we will discuss about Microorganisms. After reading this essay you will learn about: 1. Hidden World of Microorganisms 2. General Classification of Microorganisms 3. Importance in Human Welfare. Contents: Essay on the Hidden World of Microorganisms Essay on the General Classification of Microorganisms Essay on the Importance of Microorganisms in Human [ ].

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A microorganism (from the Greek: μικρός, mikros, "small" and ὀργανισμός, organismós, "organism") is a microscopic organism, which may be a single cell[1] or multicellular organism. A microorganism essay is a scientific writings and hence it offers very low space for creativity. You should base your ideas strictly on the experiments that have been carried out .