Archive for February 2012

FLEAS   Leave a comment

Reproduced courtesy of David Spears © Clouds Hill Imaging Ltd.

DEFINITION:1 any of an order (Siphonaptera) of small, flattened, wingless insects with large legs adapted for jumping: as adults they are bloodsucking parasites on mammals and birds.

The flea is one of the most troublesome of insects and one of the most dangerous. Rat fleas carry the germs of bubonic plague from rats to man. They also spread the germs of a type of typhus fever.

Fleas are tiny insects with bodies thin and flattened from side to side much as a fish is flattened. This makes it easy for them to slip quickly about among the hairs of animals upon which they live, for all fleas are parasitic.

Fleas have no wings, but their long, frog like hind legs make them wonderful jumpers. The head has a long, sharp sucking beak that the insect uses for puncturing skin and sucking blood.

The eggs of the female flea become scattered in places where animals sleep and in rugs and carpets. The larvae, or young, are worm like and have biting mouth parts They live in animal tissues and waste.

Fleas infest rats, dogs, cats, hogs, rabbits, pigeons, and poultry. Animal fleas can be destroyed by rubbing an insecticidal dust into the host animal’s fur and by applying the dust to the animal’s sleeping place, in floor cracks, behind baseboards, and in ventilator openings. Since some insecticides are poisonous to some animals that harbour fleas, the label should always be read to ensure that the preparation is safe for a given animal.

There is a kind of flea that prefers to live upon human beings. This species does not occur in the United States to any great extent.

The scientific name of the dog flea is Ctenocephalides canis; of the cat flea, C. felis; of the man flea, Pulex irritans. There are about 500 known species of fleas. All fleas constitute the order Siphonaptera.

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Posted 2012/02/29 by Stelios in Education

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FASTING   2 comments

A deliberate self-denial of food and drink, usually for religious or ethical reasons, is called fasting. The word is probably derived from a Teutonic or Germanic term meaning “to be strict” or “to observe.” In addition to fasting, many religions also have dietary restrictions: certain foods are not to be eaten by believers of a certain faith. Judaism and Islam, for instance, have regulations against the eating of certain kinds of meat; and in Islam drinking alcoholic beverages is also forbidden.

The most common motives for fasting are religious ones. In a religious fast there are three primary purposes: self-control over the body and its appetites; focusing the mind on God or prayer; making sacrifice to God (or the gods) for offences committed. The Western religions of Judaism, Christianity, and Islam have, from their inception, set aside certain times in the year for regular fasting observances.

Yom Kippur (or Day of Atonement), most sacred holiday of Judaism, observed on the 10th day of Tishri (September or October) with prayer and fasting.

Although the number of occasions on which fasting is practised has tended to diminish over the centuries in all religions, most branches of Judaism still observe a Yom Kippur (Day of Atonement) fast in the fall. Early Christianity developed a number of fasting periods: food was not eaten on Fridays in commemoration of the death of Jesus Christ.

Good Friday, the Friday before Easter; observed in churches as the anniversary of the crucifixion of Christ; legal holiday in some states of the U.S.

Later a period of 40 fast days before Easter, called Lent, was set aside to allow Christians to meditate on the sufferings of Jesus. In the 20th century the number of fast days has been dramatically reduced by the Roman Catholic church to two: Ash Wednesday and Good Friday the beginning and end of Lent. The church formerly required abstinence from eating meat on most Fridays and certain other days, but this did not include any restriction on the amount of food eaten. Protestant churches generally leave fasting to individual choice. In Islam abstention from food and drink is required of all Muslims from dawn until dusk each day of the month of Ramadan.

In primitive religions and among believers in present-day animism, fasting is used for several purposes: as a means of entreating spirits; from fear that some foods are either dangerous or holy; and by tribal priests to induce visions.

Fasting may also be politically motivated. Often called a hunger strike in the 20th century, it has been used against governments to gain specific objectives. In the Soviet Union fasting has been a common tactic by political or religious dissidents to obtain visas to leave the country. During the 1960s in the United States, fasting was one of the tactics used by the proponents of the civil rights movement and by opponents to the war in Vietnam.

Fasting has also been associated with promoting good health, either actual or perceived. In the early 20th century, American physical culturist and publisher Bernarr Macfadden advocated periods of fasting, among other things, for better health. Fasting is sometimes part of popular faddish diets for rapid loss of weight. The disorder anorexia nervosa involves fasting or near-fasting. It is especially prevalent in teenage girls.

Posted 2012/02/27 by Stelios in Education

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GENETIC ENGINEERING (Part 1 of 2)   Leave a comment

DEFINITION: the branch of biology dealing with the splicing, and recombining, of specific genetic units from the DNA of living organisms: it is used to modify the existing genetic codes to produce new, or improved, species, valuable biochemicals.

1865: The birth of genetics. It was unfortunate for the biological sciences that Gregor Mendel was an obscure Austrian monk. His pioneering work in the field of genetics was being done at the time that Charles Darwin’s publications on evolution were beginning to create worldwide controversy, but Mendel’s work would remain unknown for years.

Mendel became an Augustinian monk in 1843, but his abilities in mathematics and the sciences were evident. His experiments on the principles of heredity were begun in about 1856 in what is now Czechoslovakia. By crossing various strains of peas with one another, Mendel found that traits were passed on from generation to generation in what he called “discrete hereditary elements” in sex cells, or gametes.

Mendel reported the results of his experiments to a local society for the study of natural science in 1865 and published his findings in the society’s journal. They were as good as buried there for the next 35 years. Although the journal found its way to libraries in Europe and North America, few paid any attention to his writings. When other botanists obtained results similar to Mendel’s, they began searching through earlier writings on the subject. Only then was Mendel’s 1865 research revealed. His “discrete hereditary elements” are now called genes, and the new science once called Mendelism is known as genetics.

1953: Discovery of DNA structure. The full name of DNA is deoxyribonucleic acid. It carries the codes of genetic information that transmit inherited characteristics to successive generations of living things.

DNA was discovered in 1869 by Friedrich Miescher. In 1943 its role in inheritance was demonstrated. In 1953 its structure was determined by an American biochemist, James D. Watson, and an English physicist, Francis H.C. Crick. Watson and Crick showed the structure to be two strands of a phosphoryl-deoxyribose polymer arranged as a double helix. Watson and Crick were awarded the Nobel prize in physiology or medicine in 1962.

1973: Biotechnology. Two American biochemists, Stanley H. Cohen and Herbert W. Boyer, inaugurated the science of genetic engineering and its associated field of biotechnology in 1973. They showed that it was possible to break down DNA into fragments and combine them into new genes, which could in turn be placed in living cells. There they would reproduce each time a cell divided into two parts.

Genetic engineering makes it possible to modify existing organisms or create organisms that already exist in the human body but that are difficult to isolate. For example, one early product was a genetically engineered form of insulin, used in the treatment of diabetes. Other genetically engineered products include interferons, which are used in the treatment of viral infections and showed promise in the treatment of various forms of cancer. Scientists hope that genetically engineered products will someday prevent or cure such genetic disorders as muscular dystrophy and cystic fibrosis.

Genetic engineering also opens the possibility of creating entirely new organisms. In 1980 the United States Supreme Court ruled that newly developed organisms could be patented, thus giving ownership rights to the companies that made them.

Chromosome, microscopic, threadlike part of the cell that carries hereditary information in the form of genes; among simple organisms, such as bacteria and algae, chromosomes consist entirely of DNA and are not enclosed within a membrane; among all other organisms chromosomes are contained in a membrane-bound cell nucleus and consist of both DNA and RNA; arrangement of components in the DNA molecules determines the genetic information; every species has a characteristic number of chromosomes, called the chromosome number; in species that reproduce asexually the chromosome number is the same in all the cells of the organism; among sexually reproducing organisms, each cell except the sex cell contains a pair of each chromosome.

Each human cell holds a vast storehouse of genetic information in some 100,000 genes, which code for individual biochemical functions, strung out along 46 chromosomes. Collectively, this storehouse forms the human genome. The techniques of genetic engineering allow scientists to identify specific genes, to remove any one of those genes from an organism’s chromosome, to clone or make a large number of identical copies of that gene, to analyse a copy in detail, to modify it, and to reinsert it into the genetic material of the organism from which it was derived or into the genetic material of a similar or very different organism.

The development of genetic engineering has had a great influence on science and business and has begun to radically alter medicine and agriculture. One of the first steps in shedding new light on human evolution and in controlling or altogether eliminating many diseases was taken in the early 1990s. Scientists mapped, or took apart, the smallest human chromosomes: the Y chromosome and chromosome 21. Breaking these chromosomes into small pieces allowed researchers to reproduce these segments in large quantities. Researchers believe that this, in turn, will lay the groundwork for mapping and eventually controlling all genes, including those that may be responsible for certain diseases.

Recombinant DNA, genetically engineered DNA prepared in vitro by cutting up DNA molecules and splicing together specific DNA fragments; usually uses DNA from more than one species of organism.

Smith, Hamilton O. (born 1931), U.S. microbiologist, born in New York City; with U.S. Public Health Service 1962-67; at School of Medicine of Johns Hopkins University from 1967, professor from 1973; received 1978 Nobel prize for research on effect of restriction enzymes on DNA molecules.

Nathans, Daniel (born 1928), U.S. microbiologist, born in Wilmington, Del.; professor school of medicine of Johns Hopkins University from 1967, director microbiology department from 1972; received 1978 Nobel prize for research on effect of restriction enzymes on DNA molecules.

Posted 2012/02/25 by Stelios in Education

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GENETIC ENGINEERING (Part 2 of 2)   Leave a comment

Genetic engineering had its origins during the late 1960s and early 1970s in experiments with bacteria, viruses, and small, free-floating rings of deoxyribonucleic acid (DNA) called plasmids, found in bacteria. While investigating how these viruses and plasmids move from cell to cell, recombine, and reproduce themselves, scientists discovered that bacteria make enzymes, called restriction enzymes, that cut DNA chains at specific sites. The 1978 Nobel prize for physiology or medicine was shared by the discoverer of restriction enzymes, Hamilton O. Smith, and the first people to use these tools to analyse the genetic material of a virus, Daniel Nathans and Werner Arber.

The action of restriction enzymes is the crux of genetic engineering. DNA is made up of two long intertwined helices. The backbone of each helix is constructed from a chain of organic compounds called nucleotides. DNA is the carrier of genetic information; it achieves its effect by directing the synthesis of proteins. DNA is composed of four different nucleotides, repeated in specific sequences that form the basis of heredity. Restriction enzymes recognize particular stretches of nucleotides arranged in a specific order and cut the DNA in those regions only. Each restriction enzyme recognizes a different nucleotide sequence. Thus, restriction enzymes form a molecular tool kit that allows scientists to cut the chromosome into various desired lengths, depending on how many different restriction enzymes are used. Each time a particular restriction enzyme or set of restriction enzymes is used, the DNA is cut into the same number of pieces of the same length and composition. At least 80 restriction enzymes are now known.

When restriction enzymes are used along with other enzymes that tie together loose ends of DNA, it becomes possible to remove a bit of DNA from one organism’s chromosome and to insert it into another organism’s chromosome. This allows scientists to produce new combinations of genes that may not exist in nature. For example, a human gene can be inserted into a bacterium or a bacterial gene into a plant.

So far, however, there are limits to this ability. Scientists are unable to start with only test tubes full of nucleotides to create a whole new organism. They must start with the complete genetic material of an already existing organism. Thus, genetic engineering allows the addition of only one or a small number of new characteristics to an organism that remains essentially the same. In addition, only characteristics that are determined by one or a few genes can be transferred. The technology of genetic engineering does not enable scientists to transfer behavioural traits, such as intelligence, that are a complex mixture of many genes and the effects of cultural conditioning.

In practice, genes to be inserted into bacteria are first recombined into a plasmid, which replicates and travels independently from its bacterial host. The modified plasmid is then inserted into another bacterium.

At the time that these methods became available, it was not known whether DNA could be replicated and expressed in a foreign organism. Experiments done in the mid-1970s with these techniques, however, showed clearly that a human gene could be reproduced by a bacterium along with its own genetic material and that the bacterium could make the protein coded for by the human gene. This opened the way to making large amounts of human hormones and other significant human substances in the laboratory, a much easier route than isolating these substances from blood or cadaver glands.

One of the first areas in which genetic engineering exerted an influence was the medical field. Genetic engineering techniques allowed the production of large amounts of many medically useful substances, particularly the class of biological compounds called peptides. Peptides are short proteins. Many of the most important chemical messengers in the body are peptides. These include hormones such as insulin, nervous system messengers such as the endorphins, and regulatory messengers from the hypothalamus that control production of hormones by the pituitary gland, the gonads, and the thyroid gland, among others.

Several biologically useful peptides were made and tested in clinical trials during the late 1970s and early 1980s. The first genetically engineered product to be approved for human use was human insulin made in bacteria. Insertion of the human insulin gene into bacteria was accomplished by the pioneer genetic engineering company Genentech. Testing, approval for medical use, and large-scale production of genetically engineered human insulin were carried out, and the first diabetic patient in the world was injected with human insulin made in bacteria in December 1980, making this the first genetically engineered product to enter medical practice. (Genetically engineered products are often identified by the prefix r, for “recombinant.” Thus, genetically engineered insulin is sometimes written, r-insulin.)

The interferons are another medically important group of peptides that became available in abundance only after the development of genetic engineering techniques. Interferon was useful for treating viral infections, and there were strong indications that it might be effective against some cancers. Before the advent of genetic engineering techniques, it took laborious processing of thousands of units of human blood to obtain enough interferon to treat a few patients. And this interferon was not very pure. With the insertion of the interferon gene into bacteria, large amounts of very pure interferon became available. This supply allowed trials of interferon in the early 1980s against more than ten different cancers, including the particularly virulent form of Kaposi’s sarcoma often found in persons with acquired immunodeficiency syndrome (AIDS). The human body makes more than 50 different varieties of interferon. It is thought that some types of interferon may be more effective against cancer than others.

Other medically useful human peptides that have been made widely available because of genetic engineering are human growth hormone, which is used to treat persons with congenital dwarfism and was formerly obtained from cadaver pituitary glands, and tissue-type plasminogen activator (t-PA), which is a promising new treatment for persons who suffer a heart attack.

Vaccines

Genetic engineering techniques have also been investigated as a means to produce safer new vaccines. The first step is to identify the gene in a disease-causing virus that stimulates protective immunity. That gene is isolated and inserted into a harmless virus, such as vaccinia, the virus used to immunize against smallpox. The recombinant vaccinia virus is used as a vaccine, producing immunity without exposing people to the disease-causing virus. In the case of viruses about which little is known, such as the AIDS virus, this extra margin of safety is crucial.

Recombinant techniques may be useful in making vaccines against organisms for which no vaccines could be made by traditional methods. These include possible vaccines against the tropical parasites that cause schistosomiasis and malaria.

Diagnosis, Therapy, and Research

Genetic engineering is also being used in the prenatal diagnosis of inherited diseases. Restriction enzymes are used to cut apart the DNA of parents who may carry a gene for a congenital disorder, and the DNA pattern of cells from the fetus is compared. In many situations the disease status of the fetus can be determined. Currently this technique is applicable to thalassemias, Huntington’s disease, cystic fibrosis, and Duchenne’s muscular dystrophy.

A future medical use of genetic engineering is for gene therapy. Persons who are born with a congenital disorder resulting from a defective gene could have a sound gene inserted into their cells, preventing the manifestations of the disease. The era of gene therapy began on Sept. 14, 1990, when the first therapeutic, genetically engineered cells were infused into a 4-year-old girl with adenosine deaminase (ADA) deficiency, an inherited life-threatening immune deficiency. The infused cells were lymphocytes from the girl’s own blood, into which researchers had inserted copies of a missing gene that directs production of ADA. On Jan. 29, 1991, gene therapy was used for the first time to treat cancer, when two patients with advanced skin cancer were infused with their own white blood cells after the cells had been genetically altered to produce a tumour-killing protein. Many obstacles must be overcome to achieve the promise of gene therapy, but its value could be immense.

Ribozymes, RNA molecules that act like enzymes to cut and splice themselves.

Genetic engineering has allowed discoveries that could not have been made any other way. One of the most important is the discovery of oncogenes, specific genes that play an important part in causing some cancers. The identification and isolation of oncogenes depended on being able to cut cancer-causing DNA into manageable segments and finding the specific segments that were responsible for transforming normal cells into cancer cells. Discovery of ribozymes RNA molecules that act like enzymes to cut and splice themselves gave scientists hope for a new way of destroying the expression of unwanted genes. (RNA, along with DNA, is a carrier of genetic information.)

Agricultural advances are also expected from genetic engineering. Some of the earliest recombinant organisms made were a soil bacterium that was induced to make a toxin against a worm that destroys corn roots, a bacterium engineered to make potato and strawberry crops more frost-resistant, and a tobacco plant bearing a bacterial gene that protects against herbicides. Work on agricultural applications of genetic engineering proceeds slowly because recombinant organisms must be released outdoors in test fields to find whether they work. They cannot be tested only in a contained laboratory. Government regulatory agencies and ecological scientists are wary of the possible adverse consequences of releasing recombinant organisms, particularly fast-reproducing bacteria, into a field plot. No one knows how likely it is that such organisms may escape the field, grow in some situation in which they are not wanted, and cause unexpected effects.

National Institutes of Health, established 1887 at Marine Hospital, New York, N.Y.; present name from 1948.

Public debate about the safety of recombinant organisms began in the 1970s. Government bodies were set up to screen proposed experiments and institute safety guidelines. Chief among them was the Recombinant Advisory Committee of the National Institutes of Health. For many years the public was concerned about the safety of laboratory research with recombinant organisms. As research has continued and no safety hazards have become evident, public concern has abated somewhat.

Assisted by William A. Check.

Posted 2012/02/25 by Stelios in Education

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CRICKETS, GRASSHOPPERS, AND KATYDIDS   Leave a comment

DEFINITIONS:

CRICKET1 any of various families (esp. Gryllidae) of generally dark-coloured, leaping, orthopteran insects usually having long antennae: the males produce a characteristic chirping noise by rubbing parts of the fore wings together 2 a small metal toy or signalling device that makes a clicking sound when pressed.

GRASSHOPPER1 any of various families (esp. Acrididae) of leaping, plant-eating orthopteran insects with powerful hind legs adapted for jumping 2 a cocktail made of green creme de menthe, cream, and, usually colourless creme de cacao 3 [Mil. Slang] a small, light aeroplane for scouting, liaison, and observation.

KATYDID – any of several large, green orthopteran insects (esp. family Tettigoniidae) having long, slender antennae and long hind legs: the male has highly developed stridulating organs on the fore wings, that produce a shrill sound.

Crickets, grasshoppers, and katydids are among the most musical of insects. More than 10,000 species live throughout the world.

Orthopterans, as they are sometimes called, characteristically have two pairs of wings. The outer, forward pair is thick and tough and used only as a protective covering for the filmy rear wings. The thin rear wings move when the insect is flying. The forward wings are held stiff and motionless. When the rear wings are not in use, they fold up like fans and lie along the back beneath the forward pair. Many orthopterans are wingless or have small wings that are useless for flying.

Most species have legs that are highly efficient for jumping. The front and middle pairs are short. The rear pair is longer than the entire body and very powerful. The upper section of the hind legs, called the femur, has very strong muscles. The lower part, called the tibia, has sharp spines that are located at the end near the foot. When a grasshopper, for example, prepares to jump, it digs the spines into the ground, bringing the tibia and femur together. Then it straightens its legs and shoots forward like a released spring. Some kinds of grasshopper can jump more than 100 times their length.

Crickets, grasshoppers, and katydids are among the noisiest and most musical of the insects. The chirp of crickets has even been considered a blessing in Europe and America. In his story ‘The Cricket on the Hearth’, Charles Dickens wrote about a cricket that sings when things are going smoothly and is silent in times of trouble. The Chinese, who consider the cricket a creature of good omen, predict good luck for the house with many crickets.

These insects produce sound by rubbing particular parts of the body against one another. In most species, only the males make sound, primarily as a means of attracting mates or as identification to other males. The cricket’s song is produced when males scrape the rough surfaces of the wing covers together. Katydids and grasshoppers also use their wings to make a chirruping noise. Like crickets, katydids rub their wings against one another. Grasshoppers, however, usually rub a leg in a sawing motion across a wing to create the sound.

Orthopterans are well equipped for hearing and seeing. They have large, compound eyes, which are groups of seeing units, that allow them to see in all directions at once. Simple eyes, which detect light but do not form a visual image, may also be present in the head region around the compound eyes. Hearing is also well developed as might be expected in such a noisy group. Two structures known as tympani are located on the legs or on the body. A tympanum acts as an ear.

Another sensory device of these insects is the antenna, two of which are located on the head in front of the compound eyes. The antennae, or “feelers,” are segmented and are used as organs of smell, touch, and sometimes hearing. The majority of crickets, grasshoppers, and katydids have chewing mouth parts Most are vegetarians but some specialize on a diet of other insects.

Crickets

 

About 1,000 kinds of crickets have been discovered by scientists. Most do not fly, though hard, shiny wing covers lie across the back. Under the outer wings are two tiny wings that are useless for flight. Nonetheless, crickets can be extremely quick and lively and can jump long distances. Crickets have a pair of long, slender antennae.

The common field cricket of the United States and southern Canada is black and about 1 inch (2.5 centimetres) long with antennae longer than its body. It feeds chiefly on plant foliage but will eat other small insects. During the summer it lives in fields. Beneath rocks, wood, or other debris it digs a burrow that has a small chamber at the end. The burrow is used for shelter when the cricket is not feeding.

During the fall the female deposits in the ground eggs that hatch the following summer. But, unlike most other insects, crickets do not go through larval and pupal developmental stages after hatching from the egg. In these stages the youngster looks nothing like the adult. Instead crickets undergo what is known as incomplete metamorphosis, a characteristic of other members of the order Orthoptera.

The newly hatched cricket, called a nymph, is similar in appearance to the adult but has no wings. Nymphs grow in a series of moults, during which they literally burst out of their skin, emerging slightly larger after each shedding.

Most adult crickets die in the late autumn, but some that find a warm corner in a house may spend the winter there. One form, the house cricket, is particularly common around people’s living quarters. The house crickets of Europe and northern Africa are straw-coloured and have been introduced to many regions of the world, including North America. They are about 1/2 inch (1.3 centimetres) long.

Mole crickets are burrowing forms that have huge forelegs and claws adapted for digging. Their bodies are covered with fine hairs. During the day they remain underground. Some species fly around at night. Mole crickets are well known in Europe and North America, and many species live in tropical areas.

Tree crickets are a major group. Some, such as the common snowy tree cricket, are light green in colour Tree crickets are among the most persistent music makers. Some species sing at night, others during the day. Because the song of crickets slows down as the temperature drops, a rough estimate of the temperature can be made by counting the number of tree cricket chirps. The temperature in degrees Fahrenheit is determined by dividing the number of chirps per minute by 4 and adding 40.

Numerous other crickets exist around the world, including such specialized forms as the ant-loving crickets that live in ant mounds. Cave, or camel, crickets are recognizable by their extreme hump-backed appearance and long antennae. They inhabit caves or other dark, damp places.

Grasshoppers

 

Grasshoppers are closely related to crickets. The most common varieties belong to the group known as the short-horned grasshoppers. Although some of the more than 5,000 species of grasshopper are wingless, most have well-developed wings.

Grasshoppers usually fly only short distances. But when forced to migrate in search of food, they can fly for a series of “short hops” that total hundreds of miles. The grasshoppers that are also called locusts are among the world’s worst insect pests and have been recognized as such throughout history.

About 10 different species of grasshoppers have been known to form the enormous migratory swarms that can cause such agricultural havoc. Red locusts and desert locusts are major problems in Africa. Australia, South America, and Eurasia also have problem species. Great locust swarms have devastated crops and natural vegetation in a matter of days.

According to some reports, the grasshoppers appear on the horizon like a black storm. The roar of their wings can be deafening. When they land, they eat every living plant in sight and then move on. Modern pesticides have controlled this in most agriculturally developed areas of the world, but locust swarms still are a problem in many areas. Surprisingly, the same species that causes such problems in great numbers will often go for years living a peaceful, inconspicuous existence. Most grasshoppers, however, lead solitary lives, joining others of their species only for mating.

Grasshoppers lay their eggs in the late summer and fall. At the end of the female’s body are four short, thick prongs, together called an ovipositor. With her ovipositor she bores a hole 1 to 2 inches (2.5 to 5 centimetres) deep in the soil of fields or grassy areas. She then spreads the ovipositor apart and deposits the eggs in the hole in a mass that may total only a few eggs or may number more than a hundred. She covers the eggs with a frothy substance that hardens and forms a protective pod. The pod also provides air space for the young grasshoppers when they hatch underground. The female lays several egg masses with protective pods, each in a different hole. She may lay as many as 20 pods in a season.

As winter approaches, the adult grasshoppers die, and the young pass the winter in the egg stage. When the grasshoppers hatch in the spring, they quickly work their way to the surface and shed the membrane that covers them. The newly hatched grasshoppers look like miniatures of their parents with big heads and long legs, but their wings have not yet developed. They begin to eat green plants and grow rapidly. They moult five times in about six weeks, finally emerging as fully developed adults.

A familiar grasshopper in the south eastern United States is the lubber grasshopper, a black grasshopper measuring over 4 inches (10 centimetres) in length. These creatures sometimes accumulate in great numbers. They walk more than they fly because their colourful wings are small. They eat vegetation and have the unique behaviour of squeaking and forming a droplet of brown liquid at the mouth when picked up. They are harmless and are often used in biology courses to demonstrate insect characteristics.

Katydids

Katydids are members of a family of more than 4,000 species. They are sometimes called long-horned grasshoppers or bush crickets. Katydids usually have green or brown wings and bodies with long, thin antennae. They live in trees or low-lying vegetation. Sounds of “katydid-katydid” in the eastern United States dominate late summer nights. Katydids make the sound by rubbing a “scraper” at the base of a front wing across a “file” on the base of the other.

Although crickets and grasshoppers are generally harmless creatures to handle, katydids can inflict a painful bite. Some katydids are plant eaters, but many of them eat other insects. The tree-dwelling forms lay their eggs on leaves or branches in the autumn. The adults die during the winter, and the following spring the young hatch out of the eggs. They are pale in colour at first but turn leaf-green like the adults as they get older.

Scientific Classification

Crickets, grasshoppers, and katydids are members of the order Orthoptera and the class Insecta, which also includes cockroaches, mantids, and walking sticks. Field, house, tree, and mole crickets belong to the family Gryllidae; camel crickets to the family Gryllacridae; short-horned grasshoppers to the family Acridae; katydids and Mormon crickets and other long-horned grasshoppers to the family Tettigoniidae. The American mole crickets are in the subfamily Gryllotalpinae. The common field crickets belong to the genus Gryllus; the common katydids to the family Tettigoniidae. The scientific name of the house cricket is Acheta domestica; of the snowy tree cricket, Oecanthus fultoni; of the Mormon cricket, Anabrus simplex; of the south eastern lubber grasshopper, Romalea microptera.

Posted 2012/02/23 by Stelios in Education

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ECOLOGY (Part 1 of 3)   Leave a comment

DEFINITION:1 a) the branch of biology that deals with the relations between living organisms and their environment b) the complex of relations between a specific organism and its environment 2 Sociology the study of the relationship and adjustment of human groups to their geographical and social environments.

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwins theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

The science that deals with the ways in which plants and animals depend upon one another and upon the physical settings in which they live is called ecology. Ecologists investigate the interactions of organisms in various kinds of environments. In this way they learn how nature establishes orderly patterns among a great variety of living things. The word ecology was coined in 1869. It comes from the Greek oikos, which means “household.” Economics is derived from the same word. However, economics deals with human “housekeeping,” while ecology concerns the “housekeeping” of nature.

Interdependence in Nature

Ecology emphasizes the dependence of every form of life on other living things and on the natural resources in its environment, such as air, soil, and water. Before there was a science of ecology, the great English biologist Charles Darwin noted this interdependence when he wrote: “It is interesting to contemplate a tangled bank, clothed with plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and so dependent upon each other in so complex a manner, have all been produced by laws acting around us.”

Ecology shows that people cannot regard nature as separate and detached something to look at on a visit to a forest preserve or a drive through the country. Any changes made in the environment affect all the organisms in it. When vehicles and factories hurl pollutants into the air, animals and plants as well as humans themselves are harmed. The water they foul with wastes and silt threatens remote streams and lakes. Even ocean fisheries may experience reduced catches because of pollution.

The Balance of Nature

Each kind of life is suited to the physical conditions of its habitat the type of soil, the amount of moisture and light, the quality of air, the annual variations in temperature. Each survives because it can hold its own with its neighbours However, the continued existence of the whole group, or life community, involves a shifting balance among its members, a “dynamic equilibrium.”

Natural balances are disrupted when crops are planted, since ordinarily the crops are not native to the areas in which they are grown. Such disturbances of natural balances make it necessary for man to impose artificial balances that will maintain or increase crop production. For the effective manipulation of these new equilibriums, information on nature’s checks and balances is absolutely essential, and often only a specialist is able to provide it. For example, if a farmer were told that he could increase the red clover in his pasture with the help of domestic cats, he might ridicule the suggestion. Yet the relationship between cats and red clover has been clearly established. Cats kill field mice, thus preventing them from destroying the nests and larvae of bumblebees. As a result, more bumblebees are available to pollinate clover blossoms. The more thoroughly the blossoms are pollinated, the more seed will be produced and the richer the clover crop will be. This cat-mouse-bee-clover relationship is typical of the cause-and-effect chains that ecologists study.

The Wide Scope of Ecology

Long before a separate science of ecology arose, men in all sorts of occupations were guided by what are now regarded as ecological considerations. The primitive hunter who knew that deer had to stop at a salt lick for salt was a practical ecologist. So too was the early fisherman who realized that gulls hovering over the water marked the position of a school of fish. In the absence of calendars, men used ecological facts to guide their seasonal endeavours They planted corn when oak leaves were the size of a squirrel’s ear. They regarded the noise of geese flying south as a warning to prepare for winter.

Natural history, the study of nature in general; forerunner of the sciences of biology and ecology.

Until about 1850, the scientific study of such phenomena was called natural history, and the student of the great outdoors was called a naturalist. Afterwards, natural history became subdivided into special fields, such as geology, zoology, and botany, and the naturalist moved indoors. There he performed laboratory work with the aid of scientific equipment.

While the scientists were at work in their laboratories, other men were continuing to cope with living things in their natural settings on timber lands, on range lands, on crop lands, in streams and seas. Although these men often needed help, many of their problems could not be solved in the laboratory.

The forester, for example, wanted to know why trees do not thrive on the prairie, the desert, and the mountaintop. The rancher wanted to know how to manage his pastures so that his cattle would flourish, and how such creatures as coyotes, hawks, rabbits, gophers, and grasshoppers would affect his efforts.

As for the farmer, almost every part of his work posed problems for which scientific answers were needed. The game manager came to realize that his duties entailed much more than the regulation of hunting. To preserve the animals for which he was responsible, he had to make sure they had the right kinds of food in all seasons, suitable places to live and raise their young, and appropriate cover.

The fisherman learned that most aquatic life fares poorly in muddy and polluted waters. He became interested in land management and waste disposal when he discovered that the silt he found so troublesome came from rural areas where timber, range land, and crop land were mishandled and that the waters he fished were polluted by urban wastes. The ocean fisherman wanted to know why fish were abundant in one place and scarce in another. He needed information on the breeding habits of his catches and of the tiny animals and plants upon which they fed.

These are all ecological problems. To solve them the ecologist must understand biology the science of living things including botany and zoology. He must also understand the sciences that deal with weather, climate, rocks, earth, soil, and water.

An ecologist is concerned with both the past and the future. The present and potential condition of a field, stream, or forest cannot be understood without knowing its earlier history. For example, great stretches of light-green aspen trees may grow in parts of the Rocky Mountains while nearby slopes are covered with dark-green fir and spruce trees. This indicates that a forest fire once destroyed stands of evergreens. Aspens are the first trees capable of growing on the fire-scarred land. After about 40 years spruce and fir seeds begin to germinate in the shade of the aspens. In the course of time the evergreens can be expected to regain their lost territory.

SOME PRINCIPLES OF ECOLOGY

Ecology is a relatively young science. Its laws are still being developed. Nevertheless, some of its principles have already won wide acceptance.

The Special Environmental Needs of Living Things

One of these principles can be stated as follows: life patterns reflect the patterns of the physical environment. In land communities vegetation patterns are influenced by climate and soil. Climate has a marked effect on the height of dominant native plants. For instance, the humid climate of the Eastern United States supports tall forest trees. Westward from Minnesota and Texas the climate changes from sub humid to semiarid. At first the land has squatty, scattered trees and tall grasses or thickets. As the climate becomes drier, tall-grass prairies dominate. Finally, on the dry plains at the eastern base of the Rockies, short-grass steppe appears.

Rocky Mountains (or Rockies), chain of ranges, along e. side of North American Cordilleras from Mexico to Alaska.

Climates and plant varieties change quickly at the various elevations of mountain range. At very high altitudes in the Rockies, alpine range lands exist above the timberline. Here, the climatic factor of cold outweighs that of moisture, and tundra vegetation similar to that of the Arctic regions is nurtured. West of the Rockies, however, in basins between other mountains, the desert scrub vegetation of arid climates prevails. Near the northern Pacific coast may be found lush rain forests typical of extremely humid temperature climates.

Though moisture and temperature determine the overall pattern of a region’s vegetation, unusual soil conditions may promote the growth of un-typical plant species. Thus, even in arid climates cat tails grow near ponds and forests rise along streams or from rocky outcrops where run off water collects in cracks.

Plants and animals flourish only when certain physical conditions are present. In the absence of such conditions, plants and animals cannot survive without artificial help. Domestic plants and animals ordinarily die out within a few generations without the continued protection of man. Of all the forms of life, man seems least bound by environmental limitations. He can create liveable conditions nearly everywhere on the planet by means of fire, shelters, clothing, and tools. Without these aids, man would be as restricted in his choice of habitat as are, for example, such species as the polar bear, the camel, and the beech tree. However, given his capacity to develop artificial environments, man is able to range not only over the entire Earth but also in the heights of outer space and the depths of the ocean bottom.

Communities of Plants and Animals

Community, in biology, a group of organisms living together in a particular environment.

Closely related to the life patterns principle is the principle of biotic communities. According to this principle, the plants and animals of a given area its biota tend to group themselves into loosely organized units known as communities. The community is the natural home of each member-species.

This means that certain types of plants and animals live together in readily identified communities. Pronghorn antelope are associated with dry steppe grasslands; moose inhabit northern spruce forests; and such trees as oak and hickory or beech and maple are found together in forests. By contrast, certain living things cat tail and cactus, for example never share the same natural environment.

Large communities in turn contain smaller ones, each with its own characteristic biota. Bison, coyotes, and jack rabbits are part of the grasslands community. Fox squirrels, wood pigeons, and black bears are part of the forest community. By means of computers, ecologists have simulated communities containing various plants and animals. In this way they have been able to determine optimum populations for each of the species in a community.

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Competition in Communities

Competition is a characteristic of all communities. Plant roots in dry range lands compete for water. The trees of a rain forest compete for light. Crops compete for both of these as well as for nutrients. Competition is usually keen in areas where one type of community seems to overlap another. For example, a continuum between a shrub community and a marsh contains some aspects of both communities. Animals and plants trying to establish a foothold in such an overlap must cope with difficulties often non-existent in a stable community. Shrubs moving toward the marshy area must compete with other pioneer shrubs and reeds for light and nutrients.

Similarly, reeds attempting to invade the shrubby area must compete with shrubs and other reeds. This shows that competition may often be greatest among living things that have the same needs. For the same reason, competition may be extremely harsh within a species among wolves for meat or among cattle for grass, for example.

On the other hand, competition is sometimes modified through behavioural adjustments even cooperation among the members of a community. Shrubs are spaced widely on deserts. Birds nest in patterns that prevent overcrowding. Bees live together in a hive. Man can make similar adjustments, and unlike other species he can achieve cooperation by rational means. Yet human competition sometimes ends in wars, and wars frequently destroy the very things which the belligerents are striving to take away from one another.

Should it become necessary to control an undesirable species in a community, this can best be done by modifying the community. A rancher, for example, may discover that weedy annual plants are invading his native perennial pastures. His initial reaction might be to attack the weeds with chemical herbicides. This approach would be self-defeating since nature would provide the resultant bare soil with an unlimited supply of weed seed. To solve the problem ecologically, the rancher should modify the community by managing the degree and time of cattle grazing to permit normal growth of the native plant community, which would then crowd out the undesirable weeds.

Succession in Communities

A third major principle of ecology is that an orderly, predictable sequence of development takes place in any area. This sequence is called ecological succession. The successive changes produce increasingly mature communities from a barren or nearly barren start. Succession usually culminates in a climax, a fairly stable community in equilibrium with, and limited by, climate and soil.

At one time or another virtually all land surfaces have undergone basic climatic changes and been occupied by types of plants and animals which they may no longer be able to sustain. This, however, is not what is meant by ecological succession. It is known as biotic history, extends over the vast scale of geologic time, and is deduced from fossil remains. The future communities of an area cannot be predicted from its biotic history. Such prediction can be based only on a knowledge of ecological succession.

As soon as the first patches of soil are formed in barren areas, a series of events takes place that eventually terminates in the establishment of a climax community. This process is called primary succession. Because soil formation requires the slow weathering of rock, primary succession ordinarily spans hundreds of years. Once it begins, however, the sequence of events rarely alters. As soil formation proceeds, a succession of plants and animals appear. The last stage in this progression is the climax community.

Disclimax, an ecological community that occurs following a disturbance.

A disturbance at any point during primary succession or even at the climax can destroy the vegetation of a primary succession in whole or in part. The vegetation that follows a disturbance of this kind is called a disclimax. The disturbance can be caused by ploughing, logging, or overgrazing. When such a disturbance takes place, climate and soil are no longer the principal determinants of vegetation. The further natural growth of plants at the site of a disclimax, as contrasted with the raising of crops, is called secondary succession. This can be completed in a few years or, at most, in decades because soil has already been formed. After secondary succession restores a balance between eroded soil and vegetation, the further development of both again becomes dependent on primary succession. Wise landowners use secondary succession to restore overgrazed range lands, cut over timber lands, and abandoned crop lands They need only protect the land from further disturbances while secondary succession heals the scars of abuse.

Changes in the community during secondary succession are rapid, because every living thing contributes to its alteration. For instance, the weeds that grow on a vacant lot produce shade and increase the soil’s ability to absorb and store water. They also attract insects and birds and enrich the soil when they die and decay. The bare ground of the vacant lot is the best possible place for the pioneer sun-loving weeds to grow. Later the weeds are replaced by tree seedlings if the lot is in a forest climate, by native grasses if it is in a grasslands climate. Such changes occur until plants and animals that can make maximum use of the soil and climate are established.

The Ecosystem

A fourth key principle of ecology asserts that a community and its environment the living and the non-living constitute an ecological system, or ecosystem. Every natural community draws vital materials from its surroundings and transfers materials to it. Raw materials and decay products are exchanged continuously. Thus, in an undisturbed area basic resources are sustained, never exhausted.

Ecosystems exist on many kinds of lands, in lakes, in streams, and in oceans. They are found wherever soil, air, and water support communities. The combined ecosystems of the Earth constitute the biosphere.

Ecosystems generally contain many kinds of life. A cornfield, for example, contains more than just corn. Also present are smaller plant species, insects, earthworms, and a host of soil microbes. Each of these organisms fills a specific niche each performs an essential function in the ecosystem.

The inhabitants of an ecosystem are classified as producers, consumers, and decomposers. Green plants of any kind, whether stately oaks or tiny algae, are producers because they make their own food through photosynthesis. Animals, including man, feed on plants or on other animals and are therefore classed as consumers. Organisms that cause decay bacteria and fungi are decomposers.

Food chain, sequences in which organisms within an ecosystem feed on one another.

The sequences in which the organisms within an ecosystem feed on one another are called food chains. Usually organisms of higher biological rank feed on those of lower rank. Ecologists group the members of any food chain into a pyramid of numbers. At the base of such a pyramid are the green plants, which are the most numerous organisms in the chain. The next level might contain first-order consumers, such as the sheep that eat the green plants. At the peak of the pyramid might be second-order consumers, such as the herdsmen who feed on the sheep. When the producers and consumers of an ecosystem die, their bodies are broken down by the decomposers into nutrients used by new plants for growth. In this manner, the food chain is perpetuated.

The biosphere seems capable of sustaining life even in the absence of consumers. Without consumers, the rate of plant growth would eventually strike a balance with the rate of decay caused by the decomposers. Hence, even if all herbivores, or plant-eaters, were absent from the biosphere, plant growth could be expected to stabilize at certain levels.

Through plant growth and decay, water and carbon, nitrogen, and other elements are circulated in endless cycles. The driving force behind these cycles is the sun. Solar energy becomes converted into food through the photosynthesis of green plants and into heat through the respiration of plants and animals.

APPLICATIONS OF ECOLOGY

Ecologists are often employed to solve serious environmental problems. Early in this century, for example, southern Ohio was ravaged by a terrible flood. The inhabitants of the area, determined to prevent a repetition of the disaster, constructed large earthen dams across the valleys north of Dayton to contain future flood waters Since the slopes of these dams consisted of gravel with an admixture of clay, they washed away easily. It was necessary to stabilize the steep slopes quickly with plant cover. Knowing which plants would grow best in such places, an ecologist recommended the scattering of alfalfa and clover seed, followed by brome grass and Japanese honeysuckle. His recommendations were followed, and dam slopes were soon covered with a fine cohesive turf. Many of the hills on neighbouring farms lacked such cover and were quickly eroded.

In the Dust Bowl region of Texas, sandy soil in dry areas blew into great dunes after the land was ploughed for wheat. Bulldozing these dunes was thought too expensive. However, an ecologist recommended that certain plants be raised near the shifting dunes. The plants in front of the dunes caught and held the soil, while those behind them kept the rear from blowing deeper. In a short time, wind had levelled off the high dune tops and vegetation had anchored the soil.

Ecology and Wildlife Conservation

Measures for the preservation of ducks and other migratory wild fowl are examples of ecological work with animals. When these birds grew scarce, state and federal agencies sought ways to protect them and help them reproduce. At first, laws were recommended that forbade shooting the birds in the spring when they were flying north to nest. Every female killed in the spring could mean one less brood returning in the fall. Further studies showed that many of the birds’ breeding places were being destroyed when the land was drained for other uses. Some of these sites were not well-suited for the sustained growth of crops; others, where marshes and potholes once released stored water slowly, now contributed to downstream floods. Draining thus had a doubly harmful effect. Ecologists captured the endangered birds and put aluminium bands on their legs to trace their breeding places and movements. In this way it was discovered that the problem was international. As a result, the United States began to work in close cooperation with Canada and Mexico for the protection of migratory birds.

Ecologists also investigated the food habits of birds. They recognized that if proper food was unavailable, the birds would disappear even if hunting was regulated. Experts examined the stomach contents of thousands of birds from many different areas. This work led to the finding that bird food consists mainly of plant materials that thrive under natural conditions. To ensure the availability of these materials, man had to cease altering many natural communities and to stop polluting them with his wastes.

Posted 2012/02/19 by Stelios in Education

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