Spirogyra

Spirogyra commonly called “pond silk” occurs in extensive muscles in living bright green free floating algae on the surface of stagnant ponds’ slowly running streams and fresh water streams. The thallus or plant body consists of long slender thread like un-branched filaments which are slimy to touch due to mucilage on there outer wall .

A cell enlarged

Each filament is composed of a single raw of similar cylindrical cells. Each cell consists of a cell wall made up of cellulose and protein in definite within the cell wall is a parietal layer of protoplasm enclosing a large central vacuoles. In the protoplasm is embedded 1-14 chloroplast.

Each chloroplast is in the form of a constitutes a green spiral band with toothed edges hence the name spirogyra. The chloroplast has large pyrenoids in them. There is a large single nucleus one or two nucleoli and it is suspended in the middle of the cell by cytoplasmic strands

Lateral conjugation

Reproduction occurs asexually by fragmentation of the filaments and during unfavorable conditions by the formation of walled resting spores. Sexual reproduction is by conjugation. Turning of two morphologically identical cells but physiologically dissimilar gametes.

scalariform conjugation

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Posted in: Microbiology

The Influenza (Flu) Virus

ext to the common cold, influenza or "the flu" is perhaps the most familiar respiratory infection in the world. In the United States alone, approximately 25 to 50 million people contract influenza each year. The symptoms of the flu are similar to those of the common cold, but tend to be more severe. Fever, headache, fatigue, muscle weakness and pain, sore throat, dry cough, and a runny or stuffy nose are common and may develop rapidly. Gastrointestinal symptoms associated with influenza are sometimes experienced by children, but for most adults, illnesses that manifest in diarrhea, nausea, and vomiting are not caused by the influenza virus though they are often inaccurately referred to as the "stomach flu." A number of complications, such as the onset of bronchitis and pneumonia, can also occur in association with influenza and are especially common among the elderly, young children, and anyone with a suppressed immune system.

Influenza is highly contagious and is more common during the colder months of the year. Contrary to traditional belief, however, the climate itself is not directly to blame for the increase in incidence, but rather is attributable to the greater amount of time spent indoors in close proximity to other individuals during inclement weather. The influenza virus is chiefly transmitted through airborne respiratory secretions released when an infected individual coughs or sneezes. Incubation typically is from one to two days from the time of infection, and most people begin to naturally recover from symptoms within a week. The vast majority of influenza-related deaths are caused by complications of the flu rather than the actual influenza virus.

Three distinct types of influenza virus, dubbed A, B, and C, have been identified. Together these viruses, which are antigenically distinct from one another, comprise their own viral family, Orthomyxoviridae. Most cases of the flu, especially those that occur in epidemics or pandemics, are caused by the influenza A virus, which can affect a variety of animal species, but the B virus, which normally is only found in humans, is responsible for many localized outbreaks. The influenza C virus is morphologically and genetically different than the other two viruses and is generally nonsymptomatic, so is of little medical concern.

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Posted in: Microbiology

The Human Immunodeficiency Virus (HIV)

Perhaps no disease is more strongly identified with the late twentieth century than acquired immunodeficiency syndrome, commonly known as AIDS. Yet, according to a 2004 United Nations report on the state of the global AIDS epidemic, the disease has not yet begun to reduce its grip on the world population despite the fact that AIDS does not generally receive the same amount of public attention as it once did. On the contrary, infections are on the rise in many countries, including high income nations such as the United States. In 2003, nearly five million people contracted the human immunodeficiency virus (HIV) that causes AIDS, the greatest number of new infections in a single year since AIDS was first officially recognized as a disease in 1981.

The virus responsible for HIV was first isolated in 1983 by Robert Gallo of the United States and French scientist Luc Montagnier. Since that time, a tremendous amount of research focusing upon the causative agent of AIDS has been carried out and much has been learned about the structure of the virus and its typical course of action. HIV is one of a group of atypical viruses called retroviruses that maintain their genetic information in the form of ribonucleic acid (RNA). Through the use of an enzyme known as reverse transcriptase, HIV and other retroviruses are capable of producing deoxyribonucleic acid (DNA) from RNA, whereas most cells carry out the opposite process, transcribing the genetic material of DNA into RNA. The activity of the enzyme enables the genetic information of HIV to become integrated permanently into the genome (chromosomes) of a host cell.

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Posted in: Microbiology

Plant Cell Structure

Plants are unique among the eukaryotes, organisms whose cells have membrane-enclosed nuclei and organelles, because they can manufacture their own food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates, chemicals the cell uses for fuel.

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Posted in: Microbiology

Bacteria Cell Structure

They are as unrelated to human beings as living things can be, but bacteria are essential to human life and life on planet Earth. Although they are notorious for their role in causing human diseases, from tooth decay to the Black Plague, there are beneficial species that are essential to good health.

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Posted in: Microbiology

Animal Cell Structure

Animal cells are typical of the eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles. Unlike the eukaryotic cells of plants and fungi, animal cells do not have a cell wall. This feature was lost in the distant past by the single-celled organisms that gave rise to the kingdom Animalia. Most cells, both animal and plant, range in size between 1 and 100 micrometers and are thus visible only with the aid of a microscope.

The lack of a rigid cell wall allowed animals to develop a greater diversity of cell types, tissues, and organs. Specialized cells that formed nerves and muscles—tissues impossible for plants to evolve—gave these organisms mobility. The ability to move about by the use of specialized muscle tissues is a hallmark of the animal world, though a few animals, primarily sponges, do not possess differentiated tissues. Notably, protozoans locomote, but it is only via nonmuscular means, in effect, using cilia, flagella, and pseudopodia.

The animal kingdom is unique among eukaryotic organisms because most animal tissues are bound together in an extracellular matrix by a triple helix of protein known as collagen. Plant and fungal cells are bound together in tissues or aggregations by other molecules, such as pectin. The fact that no other organisms utilize collagen in this manner is one of the indications that all animals arose from a common unicellular ancestor. Bones, shells, spicules, and other hardened structures are formed when the collagen-containing extracellular matrix between animal cells becomes calcified.

Animals are a large and incredibly diverse group of organisms. Making up about three-quarters of the species on Earth, they run the gamut from corals and jellyfish to ants, whales, elephants, and, of course, humans. Being mobile has given animals, which are capable of sensing and responding to their environment, the flexibility to adopt many different modes of feeding, defense, and reproduction. Unlike plants, however, animals are unable to manufacture their own food, and therefore, are always directly or indirectly dependent on plant life.

Most animal cells are diploid, meaning that their chromosomes exist in homologous pairs. Different chromosomal ploidies are also, however, known to occasionally occur. The proliferation of animal cells occurs in a variety of ways. In instances of sexual reproduction, the cellular process of meiosis is first necessary so that haploid daughter cells, or gametes, can be produced. Two haploid cells then fuse to form a diploid zygote, which develops into a new organism as its cells divide and multiply.

The earliest fossil evidence of animals dates from the Vendian Period (650 to 544 million years ago), with coelenterate-type creatures that left traces of their soft bodies in shallow-water sediments. The first mass extinction ended that period, but during the Cambrian Period which followed, an explosion of new forms began the evolutionary radiation that produced most of the major groups, or phyla, known today. Vertebrates (animals with backbones) are not known to have occurred until the early Ordovician Period (505 to 438 million years ago).

Cells were discovered in 1665 by British scientist Robert Hooke who first observed them in his crude (by today's standards) seventeenth century optical microscope. In fact, Hooke coined the term "cell", in a biological context, when he described the microscopic structure of cork like a tiny, bare room or monk's cell. Illustrated in Figure 2 are a pair of fibroblast deer skin cells that have been labeled with fluorescent probes and photographed in the microscope to reveal their internal structure. The nuclei are stained with a red probe, while the Golgi apparatus and microfilament actin network are stained green and blue, respectively. The microscope has been a fundamental tool in the field of cell biology and is often used to observe living cells in culture. Use the links below to obtain more detailed information about the various components that are found in animal cells.

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Posted in: Microbiology

Introduction to Cell and Virus Structure

At first glance, the petal of a flower or the skin on the back of a human hand may seem smooth and seamless, as if they were composed of a single, indistinct substance. In reality, however, many tiny individual units called cells make up these objects and almost all other components of plants and animals. The average human body contains over 75 trillion cells, but many life forms exist as single cells that perform all the functions necessary for independent existence. Most cells are far too small to be seen with the naked eye and require the use of high-power optical and electron microscopes for careful examination.

The relative scale of biological organisms as well as the useful range of several different detection devices are illustrated in Figure 1. The most basic image sensor, the eye, was the only means humans had of visually observing the world around them for thousands of years. Though excellent for viewing a wide variety of objects, the power of the eye has its limits, anything smaller than the width of a single human hair being able to pass unnoticed by the organ. Therefore, when light microscopes of sufficient magnifying capability were developed in the late 1600s, a whole new world of tiny wonders was discovered. Electron microscopes, invented in the mid-twentieth century, made it possible to detect even tinier objects than light microscopes, including smaller molecules, viruses, and DNA. The detection power of most electron microscopes used today, however, stops just short of being able to visualize such incredibly small structures as the electron orbital systems of individual atoms. Atoms are considered the smallest units of an element that have the characteristics of that element, but cells are the smallest structural units of an organism capable of functioning independently.

Yet, until the mid-seventeenth century, scientists were unaware that cells even existed. It wasn't until 1665 that biologist Robert Hooke observed through his microscope that plant tissues were divided into tiny compartments, which he termed "cellulae" or cells. It took another 175 years, however, before scientists began to understand the true importance of cells. In their studies of plant and animal cells during the early nineteenth century, German botanist Matthias Jakob Schleiden and German zoologist Theodor Schwann recognized the fundamental similarities between the two cell types. In 1839, they proposed that all living things are made up of cells, the theory that gave rise to modern biology.

Since that time, biologists have learned a great deal about the cell and its parts; what it is made of, how it functions, how it grows, and how it reproduces. The lingering question that is still being actively investigated is how cells evolved, i.e., how living cells originated from nonliving chemicals.

Numerous scientific disciplines—physics, geology, chemistry, and evolutionary biology—are being used to explore the question of cellular evolution. One theory speculates that substances vented into the air by volcanic eruptions were bombarded by lightning and ultraviolet radiation, producing larger, more stable molecules such as amino acids and nucleic acids. Rain carried these molecules to the Earth's surface where they formed a primordial soup of cellular building blocks.

A second theory proposes that cellular building blocks were formed in deep-water hydrothermal vents rather than in puddles or lakes on the Earth's surface. A third theory speculates that these key chemicals fell to earth on meteorites from outer space.

Given the basic building blocks and the right conditions, it would seem to be just a matter of time before cells begin to form. In the laboratory, lipid (fat) molecules have been observed joining together to produce spheres that are similar to a cell's plasma membrane. Over millions of years, perhaps it is inevitable that random collisions of lipid spheres with simple nucleic acids, such as RNA, would result in the first primitive cells capable of self-replication.

For all that has been learned about cells in over 300 years, hardly the least of which is the discovery of genetic inheritance and DNA, cell biology is still an exciting field of investigation. One recent addition is the study of how physical forces within the cell interact to form a stable biomechanical architecture. This is called "tensegrity" (a contraction of "tensional integrity"), a concept and word originally coined by Buckminster Fuller. The word refers to structures that are mechanically stable because stresses are distributed and balanced throughout the entire structure, not because the individual components have great strength.

In the realm of living cells, tensegrity is helping to explain how cells withstand physical stresses, how they are affected by the movements of organelles, and how a change in the cytoskeleton initiates biochemical reactions or even influences the action of genes. Some day, tensegrity may even explain the mechanical rules that caused molecules to assemble themselves into the first cells.

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Posted in: Microbiology