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FLOWERS (Part 2 of 2)   Leave a comment

Avoiding Self-Pollination

Self-pollination, transfer of pollen from the stamen of a flower to the pistil of the same flower, as distinguished from cross-pollination.

A few kinds of flowers are self-pollinating; that is, they can be fertilized with their own pollen. In most cases, however, nature takes great care to prevent self-pollination. Cross-pollination usually produces more vigorous plants. This requires the transfer of pollen from one plant to the stigma of another plant of the same species.

Flowers avoid self-pollination in several ways. In some cases the stamens and pistils mature at different times. In other flowers the stamens are shorter than the pistils and hence do not deposit pollen on their own stigma. Wind-pollinated flowers usually bear the stamens and pistils in separate flowers. Alders, birches, walnuts, and hickories bear catkins with pistillate flowers on some branches and catkins with staminate flowers on other branches. Corn has the pistils and stamens on different parts of the same plant. The tassel bears the staminate flowers; the ear bears the pistillate flowers. These are known as monoecious (of the same household) plants. A few trees, such as cottonwoods and willows, carry the separation even further, with the staminate flowers on one tree and the pistillate on another. These are known as dioecious (of two households) plants.

How Fruit Develops

After fertilization of the ovule has taken place the petals, sepals, stamens, and usually the upper part of the pistil fall off. Now, as the ovules grow into seeds (embryo plants), the ovary, or seed case, also changes. In some plants it turns into a fleshy covering, called fruit. The ovary wall separates into two layers. The inner layer becomes a hard shell, called a stone, or pit, which encloses the seed. The outer layer forms the pulpy portion of the fruit. The peach, plum, cherry, and apricot are examples. In the case of berries the entire ovary becomes a fleshy mass in which the seeds are embedded. In the apple, pear, and quince, the ovary and its seeds become the core of the fruit. The pulpy part, which is eaten, is the modified calyx.

The ovaries of many plants develop into so-called dry fruits capsules, pods, nuts, and acorns. Like the fruits and berries, they protect the seeds and help scatter them when they are mature. Another kind of dry fruit is the achene. In this case the ovary wall becomes a coating of the single seed. It does not open at maturity, as the pods and capsules do, to release the seed. Achenes are developed by flowers that produce but one ovule, such as the individual flowers of the composites. The style of the pistil sometimes remains attached to the achene as a long, feathery tail that carries the seed away on the wind. The most common flower with seeds that are readily scattered by the wind is the dandelion, regarded by most people as a weed.

The Origin of Flowers

At least 250,000 species of flowering plants are known. All of them descend from a primitive ancestor that no longer exists. The most primitive modern flowers are the members of the buttercup order, Ranales. A step higher is the rose order, Rosales.

The simplest flowers are the least skilful in making seed. Many stamens mean a great deal of pollen is wasted. A large number of pistils means that many will fail to become pollinated and produce seed. All members of the buttercup order, which includes the little buttercup itself and the splendid magnolia and water lilies, and all the roses have many pistils and stamens. The most highly specialized and most successful flowers are the composites.

Two Kinds of Flowering Plants

Angiosperms (or Angiospermae), class of flowering, vascular plants of the division Magnoliophyta having seeds in an enclosed ovary.

Flowering plants belong to the phylum Tracheophyta, or vascular plants. Thus far the flowers and seed making up only one group of this phylum, the angiosperms, have been described. These are flowers that enclose their seeds within an ovary.

Another group of flowering plants, called gymnosperms, has naked, or exposed, seeds. These plants include the conifers, or cone-bearing trees, such as the pine, fir, spruce, cypress, and cedar. Cones take the place of flowers.

Cones are of two kinds staminate and pistillate. They are usually borne on different branches of the same tree. The staminate, pollen-producing cones are small and last only a few weeks in the spring of the year. The pistillate cones are the large familiar ones. The ovules, usually two in number, are located on the upper surface of each scale. The ovule consists of an embryo sac surrounded by a covering that later becomes the seed coat. In the covering is a tiny opening called the micropyle (little gate).

In late spring the pistillate cones stand upright with the scales opened wide to catch the windblown pollen. When pollen lodges between the scales, they close. Thus protected within the closed cone, the pollen sends out a pollen tube that enters the ovule through the micropyle. When the seeds in the cone are fully grown, it again opens, releasing the matured seed. All gymnosperms are wind-pollinated.

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Posted 2012/03/17 by Stelios in Education

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CORN (Part 2 of 2)   Leave a comment

How Experimenters Developed Hybrid Corn

In 1905 George H. Shull and Edward M. East began developing new kinds of corn by placing pollen from one desirable strain of corn onto the silks of another strain. The process produced cross-bred strains called hybrid corn. After World War I, Henry A. Wallace (who became secretary of agriculture in 1933) and Lester Pfister began hybridizing experiments. By 1926 they had made hybrid pollinization completely workable.

The hybrid plants are remarkable growers. They commonly grow to be 18 or 20 feet tall; some have grown as high as 28 feet. A more important factor is that they have added millions of dollars to the income of corn farmers.

Before farmers had hybrid corn, an average acre of corn yielded 30 bushels. But farmers had to spend the money they received for 25 bushels to pay their costs for each acre planted, leaving only 5 bushels an acre for profit. Hybrid corn has raised the national average to more then 95 bushels an acre. Some states average more than 130 bushels an acre.

A hybridizer produces hybrid seed by first inbreeding. This fixes desirable qualities in the seed. He covers the ears of selected plants to keep airborne pollen from the silk. Later, he takes pollen from the tassels of a plant and dusts it on the silks of the same plant. After inbreeding each strain for several generations, he starts cross-breeding He takes pollen from the tassel of a plant having one desirable strain and dusts it on the silk of a plant with some other strain. The cross-bred product, or hybrid, has the qualities of each parent strain.

Next comes double-crossing. The experimenter dusts pollen from one hybrid onto a hybrid with two other strains. The seed from this cross produces a super corn with four strains bred in. This corn is sold to farmers as seed. Their crop cannot be used as seed next year because hybrid corn is not self-perpetuating. Farmers must buy new seed each year. Great use of hybrid corn threatens the supply of corn pollinated naturally. This loss would restrict improving hybrid strains and prevent developing new ones. To preserve seed of native varieties, the federal government stores seed in corn banks.

Planting and Cultivating

A strong, full crop of corn comes from fertile soil, good seed, thorough cultivation, and clean culture. The soil should be easily worked, well drained, and rich in plant food. The dark loam of the Midwestern United States is particularly well adapted for corn. The farmer chooses the seed to suit conditions on his land. In dry regions he may plant corn in deep furrows. If rainfall is plentiful he puts the seed down in hills or in drills. Once the plant starts to grow, cultivation must never be deep, or the tender, grass like roots will be injured.

Corn draws heavily on the plant food in the soil. Production is higher when corn crops are rotated on a three-year cycle. The first year a legume, such as alfalfa or sweet clover, builds up the soil with nitrogen and humus. The next year corn grows tall on these, its favourite foods. The third year a small grain is planted. Then the cycle is renewed with a legume.

Different Ways of Harvesting

If the farmer wants to store the whole plant in a silo, he cuts the corn while it is still green. If the corn is to be used for grain, it is not harvested until it is fairly dry. The ears may be picked by hand from the standing corn and husked and thrown into a wagon. On most farms mechanical corn pickers are used.

Some farmers turn cattle in to feed on the corn stalks after the ears are picked. Others cut the stalks, tie them into shocks, and let the ears get dry before husking. Many livestock raisers turn hogs into the ripe fields to feed and fatten on the corn. This method is called hogging down.

Fighting the Enemies of Corn

Corn ear worm (also called tomato fruit worm, or tobacco bud worm, or cotton boll worm), larva of a moth (Heliothis armiger); names vary depending on the various plants it infests; larvae on corn first eat the leaves, then the ears; pupation occurs in the ground; winter ploughing in North kills many pupae.

More than 350 insect pests attack the grain. The most destructive are the corn ear worm, the European corn borer, and the corn root worm Fungus growths, such as smut and various rots, are costly foes. In many cases insecticides are too expensive to be practical. Therefore the farmer uses the less expensive methods of clean culture and crop rotation. Clean culture means harvesting or destroying every part of the plant. Careful farmers either burn or plough under the stubble. This rids the cornfield of pests that live above the ground. Crop rotation suppresses root pests that live on corn by depriving them of food for one or two years.

Composition of a Corn Kernel

A kernel of corn is wrapped in a tough, fibrous outer hull (bran). Inside is the germ, or embryo, from which the new plant develops. Around the germ is a food supply called endosperm. This is chiefly starch. When the kernel germinates it draws its nourishment from the endosperm until it can put forth roots and leaves and obtain food from the soil and the air.

The moisture content of a kernel varies from 10 to 25 percent, depending upon weather and other conditions under which it was grown. Of the dry portion, about 70 percent is starch (carbohydrates). About 10 percent is gluten (protein), found in a shallow layer just under the hull. The remainder is fat or oil in the germ (4.5 percent), fibre in the hull, and minerals.

A Great Variety of Corn Products

All the parts of a corn kernel can be used to make products. From the whole kernels manufacturers make cornmeal, breakfast foods, and hominy. Some people make hominy at home by removing the hull with lye and cooking the whole grain. When the kernel is crushed it forms hominy grits. Distillers make alcohol and whiskey from whole corn kernels.

Since corn became so dominant a grain in American agriculture, it has naturally found its way to Europe and Asia. There, whether imported or grown locally, it is used mostly for animal feed, as it is in the United States. For humans, corn is less desirable nutritionally than for livestock. The protein value is of low quality, and corn is devoid of niacin one of the B-vitamins that is essential to humans. People who rely heavily on corn in their diets are subject to such niacin-deficiency diseases as pellagra. Corn cannot be used to make leavened bread, although it is much used in Latin America to make dough for such flat breads as tortillas.

The corn products refining, or wet-milling, industry makes a great variety of products from different parts of the corn kernel. Wet milling is so called because the kernels are steeped in tanks of water to soften them, and water is used in the processes that separate germ, gluten, and starch.

First to be separated from the kernel is the germ. Refined and crude corn oil have many uses as human and animal food and in industry. When oil is pressed from the germ a hard cake is left. It is ground into stock feed. One of the proteins in gluten is zein. A synthetic fibre is made from it. It is also used in lacquer, plastics, textile colours, and printing inks.

The final product of the wet-milling separation process is starch. The housewife, food manufacturers, and laundries have many uses for cornstarch. Paper manufacturers use more starch than any other industry to toughen and size (glaze) paper. Textile manufacturers are second. Cotton and synthetic yarns and fabrics are sized with starch.

Glucose (or dextrose, or grape sugar, or corn sugar), simple (monosaccharide) sugar found in fruits and other foods and in the blood of animals; fuels the energy needs for most living organisms.

A huge amount of starch is converted into corn syrups (glucose), sugars, and dextrose by cooking and chemical treatment. These too have countless uses in cooking and in various industrial processes. Even the steep water in which the kernels are soaked is important. Evaporated to a thick, soupy liquid, it is used as a food for the moulds that produce penicillin and other wonder drugs.

Corncobs are ground for a coarse livestock feed. They are used also in a polishing powder, insulation, and a form of sandblasting. Furfural, an oily liquid extracted from corncobs, goes into man-made fibres, drugs, and solvents. Some specially grown cobs are made into pipes for smoking.

Millions of tons of cornstalks are made into a rubber substitute, maizolith. A large quantity is used for making paper and wall board Even the gases from fermenting corn are used to make methyl alcohol.

American Indians had many kinds of corn, and there are now more than 1,000 named varieties. The smallest is the golden thumb popcorn plant, about 18 inches (46 centimetres) high. Some varieties have only eight rows of kernels; others, as many as 48 rows. Colours include white and shades of yellow, red, and blue.

The chief types of corn are pod, soft, sweet, pop, flint, and dent corn. Pod corn has each kernel enclosed in a pod or husk. Soft corn is used for corn flour and for roasting ears. Sweet corn has the smallest amount of starch; popcorn, the highest. Flint and dent corns lead all other varieties on the grain markets and for livestock feeding. The scientific name of corn is Zea mays.

Posted 2012/03/04 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.

ECOLOGY (Part 2 of 3)   Leave a comment

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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ANIMALS (Part 1 of 4)   Leave a comment

Cheetah

DEFINITION: 1 any living organism, excluding plants and bacteria: most animals can move about independently and have specialized sense organs that enable them to react quickly to stimuli: animals do not have cell walls, nor do they make food by photosynthesis 2 any such organism other than a human being, esp. a mammal or, often, any four-footed creature 3 a brutish, debased, or inhuman person 4 [Colloq.] a person, thing, concept, etc. thought of as a kind or type [today’s athlete is another animal altogether]

All living things are divided into two main kingdoms the animal and plant kingdoms and two or three other kingdoms that include bacteria, blue-green algae, and one-celled creatures with definite nuclei. What is the difference between a horse, for example, and grass? A horse moves about in the pasture eating grass. It trots toward you when you offer it a lump of sugar and shows pleasure when you stroke its head. The grass, however, is rooted to one place. It does not respond behaviourally to people or to the horse in any way.

Animals Move About and Sense Surroundings

Adult animals move freely from place to place during at least one phase of their life. Plants usually cannot move unless a force, such as the wind, causes them to move.

Most animals move freely from place to place and can sense their surroundings; that is, they can taste, smell, hear, see, and touch. Certain simple animals, such as the corals and barnacles, spend most of their lives fastened to one spot, but they are able to swim freely when they are young. Even these rooted animals have parts that move in order to capture food. Plants, however, cannot shift about at their own will. They react to heat, light, chemicals, and touch, but their responses are involuntary and automatic, quite different from those of animals.

All living things are made of cells. The walls of plant and animal cells are different.

Cellulose, complex carbohydrate consisting of 3,000 or more glucose units; basic structural component of plant cell walls; 90% of cotton and 50% of wood is cellulose; most abundant of all naturally occurring organic compounds; indigestible by humans; can be digested by herbivores, such as cows and horses, because they retain it long enough for digestion by micro organisms present in their digestive systems; also digestible by termites; processed to produce papers and fibres; chemically modified to yield plastics, photographic film, and rayon; other derivatives used as adhesives, explosives, thickening agents, and in moisture-proof coatings.

All living things are made up of cells of protoplasm. They may consist of a single cell, as does an amoeba, or billions of cells, as do trees and horses. The cell wall of a plant is composed of a woody material called cellulose. No true animal contains cellulose. Animal cells are bounded by a membrane composed chiefly of fat and protein.

Green plants make their own food. With the aid of the green substance called chlorophyll, they use the energy in sunlight to change carbon dioxide and water into carbohydrates and other food materials. No true animal contains chlorophyll.

Animals must eat, either directly or indirectly, the food manufactured by members of the plant kingdom. A horse cannot stand in the sun and wait for its body to make fat and proteins. It must move about the pasture in search of green grass. Even meat eaters for example, lions live on animals, such as zebras, which in turn subsist on plants.

The Variety of Animal Life

More than a million different kinds of animals inhabit the Earth. The exact number is not known, for new kinds are continually being discovered. They live in the seas, from the surface down to the black depths where no ray of light penetrates. On mountaintops and in deserts, in mud and in hot pools some form of animal life may be found.

Animals are infinitely varied in form, size, and habits. The smallest animals are bits of protoplasm that can be seen only with a microscope. The largest, the blue whales, may be more than 100 feet (30 meters) long and weigh 300,000 pounds (136,000 kilograms).

Some of the most familiar animals, such as dogs, birds, frogs, and fish, have a backbone and a central nervous system. They are called vertebrates, meaning animals with backbones. Animals without backbones are called invertebrates and include arthropods, worms, molluscs, and many other groups. Most of the vertebrates and many invertebrates have a head where sense organs are concentrated and have legs, wings, or fins for locomotion. Vertebrates and many invertebrates, such as the arthropods and worms, have bilateral, or two-sided, symmetry. This means that they have two mirror-image sides (a right side and a left side), distinct upper and lower surfaces of the body, and a distinct front and rear.

Some invertebrates, such as jellyfish, sea anemones, and starfish, display radial symmetry, in which the parts of the body are arranged around a central axis, similar to a wheel. Animals with radial symmetry live in marine or freshwater aquatic environments. Some drift with the currents, unable to swim in any definite direction. Others become attached to a solid object by one end and float with the mouth end upright. Tentacles arranged in a circle around the mouth sweep in food particles and ward off enemies.

One-celled animals called protozoans live in fresh and salt water. Many are shapeless creatures and cannot swim toward their food. They move along by squeezing out a finger like projection from the body. This is called a pseudopod, from the Greek meaning “false foot.” The pseudopod fastens to something solid, and the rest of the body flows into the fastened projection. The amoeba also moves in this manner. One-celled animals are very small. They are single blobs of liquid enclosed in a thin membrane and as such cannot attain a large size or a very definite shape.

Animals with Outside Skeletons and Feet

Molluscs have soft bodies that are not divided into specialized sections such as head, thorax, and abdomen. Many molluscs are enclosed in hard, hinged shells. Snails have a single large, fleshy foot located on the stomach side.

The heads of the octopus and the squid are surrounded by a circle of eight or ten tentacles that act as arms and feet. Oysters, clams, mussels, and scallops all have a single axe-shaped foot which they burrow into sand.

Most molluscs do not move around efficiently. Oysters fasten themselves to something solid and settle down for life, letting food drift to them. Scallops may move in zigzag leaps by clapping their shells together.

Joint-Legged Animals

Arthropod, animal of the phylum Arthropoda comprising invertebrates with external skeleton, segmented body, and jointed appendages.

Joint-legged animals, or arthropods, have bodies divided into segments that have specialized functions. These animals also have many jointed legs. Most arthropods are covered with a jointed skeleton made of a horny material. This outside skeleton is lighter than the shells of the molluscs The legs and muscles and many organs of the arthropod are attached to the outside skeleton.

The arthropods include insects, lobsters, crabs, centipedes, millipedes, scorpions, and spiders. They can run, jump, swim, and crawl. Some live mostly on land, while others live mostly in water. Many of the insects have wings and can fly. Arthropods inhabit most of the Earth’s environments, from the poles to the tropics, and are found in fresh and marine water and in terrestrial habitats.

How Back boned Animals Move

Vertebrates move through water and air and over the ground with great speed and skill. Birds, with their feathered wings, are the best fliers. Fish are the best swimmers. However, other vertebrates also can fly and swim. Bats fly on wings of membrane like skin. The flying squirrel glides on a broad membrane between its legs. The flying fish soars over the surface of the ocean by using its fins. Neither the fish nor the squirrel can soar great distances, however.

Some turtles swim with paddle like front legs. Some water birds can swim underwater with their wings. The mud skipper and walking catfish are fishes that walk on mud by pulling themselves along on their front fins.

Frogs, kangaroos, various cats, and some fishes are superior jumpers. Salmon leap up waterfalls when they travel from the sea to their home streams to lay their eggs. Tarpon, swordfish, and sailfish make great leaps out of the water when pursuing their prey or trying to escape an enemy.

Breathing

Animals breathe in different ways:

  • Some animals, like amoeba and sponges, let oxygen move through their cell walls.

  • Fish and tadpoles breathe with their gills.

  • Insects bring air in through pores, or holes, called spiracles.

  • Mammals, birds, and reptiles breathe with lungs.

All animals must take in oxygen in order to change food into a form that the body can use. One-celled animals that live in water absorb oxygen directly through their membranes. The sponge is a very simple many-celled animal. The surface of a sponge is covered with millions of tiny pores. Water bearing dissolved oxygen and minute food particles flows through the pores and out of the opening at the top of the sponge.

Fish and tadpoles breathe by means of gills. Insects and caterpillars take air into the body through breathing pores called spiracles.

Mammals, birds, and reptiles obtain oxygen from the air. They take it into the lungs, and the oxygen passes through membranes in the lungs into particles called red blood cells. The bloodstream then carries the oxygen to all parts of the body. Amphibians have lungs, but they also have thin, moist skins that absorb oxygen directly.

Reproduction

Sea squirt, a tunicate or saclike marine animal, so called from its habit of ejecting water when touched; belongs to the phylum Chordata.

Hydra, primitive water animal of the class Hydrozoa and the genus Hydra.

All animals reproduce their own kind. One of the most primitive forms of reproduction is by fission, in which the individual organism divides to produce a replica of itself. Some animals, such as sea squirts, reproduce by budding: lumps appear along a branchlike organ and develop into young sea squirts. Sea squirts, sponges, corals, and other creatures that bud often remain together and form large colonies. The hydra also reproduces by budding, but in time the young bud separates and goes off to live alone.

Most animals reproduce by means of eggs from the female that are fertilized by sperm from the male. The eggs of some species are deposited in a nest or in some other manner before hatching. Most species of mammal and some species of reptile and fish bear their young alive, the fertilized eggs being retained within the body of the female.

The types of reproductive behaviour among animals are almost as varied as the kinds of animals themselves. Some species, such as most insects and turtles, deposit their eggs and give them no further attention. In colonies of the social insects, such as ants and bees, a single female lays all of the eggs, and workers provide care and nourishment for the developing young in the nest. The females of some reptiles, such as the king cobra and the blue-tailed skink, and amphibians, such as the marble salamander, stay with their clutch of eggs until they hatch but provide no protection or nourishment for the young. Some fish guard their young after they are born. Crocodilians protect the eggs before hatching and the young for several months afterwards. Many birds provide not only protection but also nourishment for the developing young. Mammals, which feed their young with milk produced by the mother, provide care for their young much longer than do other classes of animals.

Posted 2012/01/29 by Stelios in Education

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CONSERVATION (Part 2 of 5)   Leave a comment

WATER CONSERVATION

Polluted water in one part of the world affects water sources everywhere. This happens because water moves through what is called the hydro logic cycle.

In the hydro logic cycle

1) water moves into the air and clouds as it evaporates from oceans, lakes, and rivers.

2) the winds that blow around the Earth blow the water vapour around until enough builds up inside a cloud to cause rain to fall.

3) wherever that rain falls, sooner or later it will flow into another body of water.

In this way, a water molecule that left the ocean near California may fall as rain in India. Unfortunately, products that pollute the water can also be carried to other parts of the world along with the water molecules.

Water is an essential natural resource. Everyone uses it. It is needed in homes for drinking, cooking, and washing. Communities must have it for fire protection and recreational activities such as swimming, boating, and fishing. Industries use it to produce electricity and to perform a large number of manufacturing processes.

Watersheds and Their Importance

Watershed (or drainage basin), area of land, of any size, from which all precipitation flows to a single stream or set of streams.

A watershed is the area drained by a river or a stream in a region. Such an area slopes toward a common land trough. Some rain runs off, or drains, over the ground surface. Run-off water forms small streams, which flow into larger ones. These eventually join to form rivers.

A natural watershed conserves water. It has clear streams and an ample cover of trees, grasses, and other plants. Plants help contribute to form a part of the topsoil called humus. Humus consists of decaying leaves and wood, bacteria, dead insects, and other plant and animal remains. It provides some of the nutrients for new plant life. Together with a network of roots, it acts as a blotter that soaks up rain. Plants break the force of falling rain and scatter the drops over leaves and branches. Some of the water returns to the air by evaporation. Part of the water used by plants is passed through their leaves into the air again by transpiration. The rest of the water sinks into the earth through countless tiny channels. Some of the spaces in the soil through which water percolates are caused by natural features of the geology or soil itself. Others are made by plant roots and burrowing animals like earthworms, insects, and moles.

The level at which the earth is permanently saturated is known as the water table. This vast underground water supply fluctuates with the seasons and the amount of rainfall. During long, heavy rains the soil may not be able to soak up all the water. Some of it runs off the surface, but in a forested watershed it moves slowly. Deep snow that melts slowly allows water to soak into the soil gradually.

When all the trees in an area have been cut down or burned off due to poor forestry practices, or grasses and other plants have been stripped off by fire, overgrazing, or poor farming practices, the watershed suffers. The water from rainfall flows over the ground’s surface instead of being absorbed by the vegetation and organic materials that would be present on a natural forest floor.

When there are no leaves and branches or grasses to break the force of falling rain and the blotter of roots and humus is gone, mud closes the channels through which water sinks into the soil. If the land is level, the water stands in stagnant pools; if it slopes, the water runs downhill into the rivers. Streams in a mismanaged watershed become brown with silt, or suspended soil, because the racing water carries soil along with it.

A mismanaged watershed can result in destructive floods in the spring because heavy rains and melting snows overflow the riverbanks. In the summer, streams, springs, and wells can dry up because little or no water has sunk into the underground reservoirs.

Water Pollution

Water can be polluted by many things. One of these is the topsoil or silt that washes into streams and rivers. This silt washes into streams and rivers from land that has been badly managed.

When silt washes into streams and rivers, two harmful things may happen.

1) Silt that floats in the water limits the amount of air in the water. Fish need air to breathe. When silt limits the air in the water, the fish die.

2) As the movement of water slows down, silt drops to the bottom of the stream beds

There are ways of controlling erosion of silt from land into streams and reservoirs. Conservationists try to make sure that the right steps are taken to prevent the silting of streams.

The silting of streams is one kind of water pollution. A heavy load of silt kills fish indirectly by reducing the amount of oxygen in the water. Then, as the flowing water slows, silt is deposited on stream beds Reservoirs behind dams also fill with silt unless erosion is stopped in watersheds above.

The main problem with our waterways is that they have been used as a garbage can for every kind of human waste that you might imagine.

Raw, untreated sewage contains:

  • garbage from individuals and businesses

  • waste products from industry

  • run-off from sewers

Raw sewage is unhealthy and can cause outbreaks of disease. It also severely pollutes the environment.

Raw sewage can be treated in special ways to make it less harmful to the environment. For example, poisonous metals and objects that take a long time to break down can be removed from the waste so it can break down faster.

Other kinds of water pollution have created other problems. Many waterways are used as dumps for household and industrial wastes. Some communities dump untreated sewage and garbage into the nearest streams. Industries contaminate the waterways when they discharge acids, chemicals, greases, oils, and organic matter into them. Such materials foul drinking water and endanger public health. They destroy commercial fisheries. They also make waterways unusable for recreational purposes. Leaks and spills from offshore oil wells and wrecked or damaged oil tankers have caused the widespread destruction of marine life.

A food chain is made up of plants and animals linked together like a chain. Each creature depends on the other creatures in the chain for food.

It takes many creatures at the bottom of a food chain to feed just one animal at the top of the chain.

If one link becomes weak, it affects all others in the chain. Here’s an example:

For a period of time humans sprayed a chemical pesticide called DDT on plants to kill bugs.

The DDT washed off the plants and into rivers, lakes, and streams. Fish ate the poison. Many fish died, but many others survived with traces of the poison in their bodies.

Some animals ate the poisoned fish. Still others ate poisoned insects. Finally, other creatures ate the animals that had eaten the poisoned fish and insects.

Since higher animals in the chain eat a large amount of the lower animals, each link was getting more and more DDT.

While large doses of DDT can kill, smaller doses do damage as well. For example, DDT causes the shells of bird eggs to be too thin. Many kinds of birds, such as the American bald eagle, poisoned by DDT, were unable to hatch young, and their numbers became smaller and smaller.

When conservationists and others saw the harm caused by DDT to various creatures such as the bald eagle, they reasoned that other creatures, including humans, were being harmed by the pesticide. Although the spraying of DDT was stopped by passing a law in the United States, it continues in other parts of the world.

The large-scale use of organic insecticides, herbicides, toxic metals, and pesticides, particularly DDT, has polluted streams and destroyed wildlife. Some pesticides tend to concentrate in the tissues of plants and animals in nature’s food chains. Thus organisms at the ends of these chains, including humans, may take in harmful amounts of pesticides deposited in their food supply.

SOIL CONSERVATION

Whenever land is stripped of its plant cover, soil is inevitably lost by erosion, the so-called silent thief. A single rainstorm can wash away centuries-old accumulations of soil from neglected or badly managed fields. Topsoil is an extremely valuable natural resource. Under this thin blanket of rich dirt and humus, in which plants grow best, is a less fertile material called subsoil. If the surface layer of topsoil is blown or washed away, the remaining subsoil cannot support plant life. The submarginal farms must eventually be abandoned.

Types of Soil Erosion

More than 700 million acres (283 million hectares) of agricultural land in the United States are subject to erosion. Some 230 million acres (93 million hectares) of crop land require constant supervision to control erosion caused by wind and water.

Dust storms are the evidence of wind erosion. Soil unprotected by plant cover simply blows away. During the 1930s millions of acres of farmlands were badly damaged by wind. Many fields lost from 2 to 12 inches (5 to 30 centimetres) of vital topsoil during this period. As a result, the entire southern Great Plains area was called the Dust Bowl.

One of the several kinds of water erosion is sheet erosion the wasting away of level land in thin layers. The deterioration may go on for years without being noticed, though the land yields successively smaller crops. A patch of subsoil showing through on some slight rise of ground may be the first sign that the land is nearly finished as a food producer.

Splash erosion is the washing away of soil by the direct battering of rain. Small channels dug in the soil by run-off are called rill erosion. The little rills run together, form a network of larger rills, and then develop into gullies. When gully erosion occurs, the land can become a desert.

Conservationists also recognize that livestock can overgraze a plot of land until severe soil erosion occurs. About 4 million acres (1.6 million hectares) of topsoil are lost every year through erosion, and about 85 percent of this is the result of overgrazing by livestock.

Although major losses of productive agricultural lands occurred in the first half of the 20th century due to erosion, a major concern today is the loss of natural habitats as a result of commercial development. Large tracts of productive land an estimated 1 million acres (400,000 hectares) each year are lost through road building, suburban housing and industrial site developments, and airport expansion. New dams often flood some of the most productive agricultural land and natural forest habitats.

Posted 2011/12/21 by Stelios in Education

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