TOEFL Reading Comprehension

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8. Zoology
8.1. All animal life on the planet Earth depends on a sufficient supply of oxygen for its day-to-day survival. The trees that dot our landscapes provide a large portion of this supply: trees take carbon dioxide from the surrounding air and in return they create a sizeable amount of oxygen. Ironically, human beings who cut down large numbers of trees to create land shelter, and energy, pose the most significant threat to the survival of the world-wide tree population.
But humans are not the only force that threatens the survival of these mighty members of the plant kingdom. Trees ?" among the oldest and largest organisms on the planet ?" face many other dangers. Lightning, fire, and other natural disasters, for example, can destroy many square miles of old-growth forest in a matter of hours. Disease-causing fungi and insect pests can also eradicate entire populations of trees within a particular region.
After humans, however, the factor which most determines whether a particular species of tree will prosper in a given area is climate. In particular, the amount of rainfall and the range of temperatures that a region experiences strongly affects the distribution of tree species.
All species of trees have evolved from plants that flourished many centuries ago in the warm and wet tropical regions of the planet. As the distribution of trees has spread to other regions the differing climates of these regions have effectively limited the types of tress that can live there. The greater the range of temperature and rainfall that a species of tree can withstand, the more adaptable it is and therefore the wider its range of distribution.
8.2. Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billion years were to pass before the first plants and animals appeared on the continents. Lifê?Ts transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.
What forms of life were able to make such a drastic change in lifestyle? The tra***ional view of the first terrestrial organisms is based on megafossils ?" relatively large specimens of essentially whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, flowed by animals that feed on the plants, and lastly by animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.
Recently, however, paleontologists have been taking a closer look at the sediments below this Silurian-Devonia geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rocks in an acid bath. The technique has uncovered new evidence form sediments that were deposited near the shores of the ancient oceans ?" plant microfossils and microscopic pieces of small animals. In many instances the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of them fossils consist of the organic remains of the organism.
These newly discovered fossils have not only revealed the existence of previously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our views about the nature of the early plant and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-forms.
8.3. The protozoans, minute, aquatic creatures each of which consists of a single cell of protoplasm, constitute, a classification of the most primitive form s of animal life. They are fantastically diverse, but three major groups may be identified on the basis of their motility. The Mastigophora have one or more long tails, which they use to project themselves forward. The Ciliata, which use the same basic means for locomotion as the Mastigophora, have a larger number of short tails. The Sarcodina, which include amoebae, float or row themselves about on their crusted bodies.
In ad***ion to their form of movement, several other feature discriminate among the three groups of protozoans. For example, at least two nuclei per cell have been identified in the Ciliata, usually a large nucleus that regulates growth but decomposes during reproduction, and a smaller one that contains the genetic code necessary to generate the large nucleus.
Protozoans are considered animals because, unlike pigmented plants to which some protozoans are otherwise almost identical, they do not live on simple organic compound. Their cell demonstrates all of the major characteristics of the cells of higher animals.
Many species of protozoans collect into colonies, physically connected to each other and responding uniformly to outside stimulate. Current research into this phenomenon along with investigations carried out with advanced microscopes may necessitate a redefinition of what constitutes protozoans, even calling into question the basic premise that they have only one cell. Nevertheless, with the current data available, almost 40,000 species of protozoans have been identified. No doubt, as the technology improves our methods of observation, better models of classification will be proposed.
8.4. Although a few protozoans are multicellular, the simplest are unicellular organisms, such as amoebas, bacteria, sarcodina, ciliates, flagellates, and sporozoans, which can be amorphous in shape and smaller than .001 inch. Cytoplasm fills the cell membrane that encloses it and functions as a barrier between cells. The membrane serves as the outer tissue, closes it and functions as a barrier between cells. The membrane serves as the outer tissue, and any compound that may destroy the cell has to penetrate it to reach the cytoplasm.
Some types of organisms are termed colonial because they represent loosely assembled groups of structurally similar and unifunctional cells. Colonial organisms maintain a symbiotic relationship within their particular environments.
Unlike colonial organisms, almost all species of animals and plants are multicelllar and include various types of specialized or somatic cells, each with its own nucleus, genetic code, and RNA. The overall size of a multicellular body is contingent on the total number of cells that comprise it, not the size of individual cells. The simplest multicelllar animals are hydras, sponges, and jellyfish, which have well-defined tissues, a cellular nucleus, and a element of cell functions. Sponges have a few specialized cells but largely resemble colonial organisms that can readily form a new individual group. If the cells of a sponge are separated, they rejoin and continue as a newly formed colonial organism.
8.5. Vibrio parahaemolyticus is a bacterial organism that has been isolated from sea water, selfish, finfish, plankton, and salt springs. It has been a major cause of food poisoning in Japan, compelling the Japanese to do several studies on it. They have confirmed the presence of V. parahaemolyticus in the north and central Pacific, with the highest abundance in inshore waters, particularly in or near large harbors.
A man named Nishio studied the relationship between the chloride content of sea water and the seasonal distribution of V. parahaemolyticus and concluded that while the isolation of the organism was independent of the sodium chloride content, the distribution of the bacteria in sea water was dependent on the water temperature. In fact, it has been isolated in high frequencies during summer, form June to September, but was not isolated with the same frequency in winter.
Within four or five days after eating contaminated foods, a person will begin to experience diarrhea, the most common symptom; this will very often be accompanied by stomach cramps, nausea, and vomiting. Headache and fever, with or without chills, may also be experienced.
8.6. A tapeworm is a parasite that lives in the intestines of humans and animals. Some tapeworms attach themselves to the intestinal wall by means of suckers in their heads. Others float freely in the intestines and absorb food through the walls of their bodies.
A tapeworm consists of numerous segments. When a new segment forms, the older ones move to the back of the animal. Each segment contains hermaphro***ic ***ual organs (that is, male and female organs). The uterus of each segment fills with eggs, which develop into embryos. Generally, when the eggs are ready to hatch, the segment breaks off and is eliminated through the host?Ts excretory system. These embryos hatch, develop into larvae, and grow to adults only if ingested by an intermediate host.
One may be infected by tapeworms by eating undercooked beef, pork, or fish. Symptoms include irregular appetite, abdominal discomfort, anemia, weakness, and nervousness.
8.7. Diapause encourages a lower-rate of metabolic activity, and certain insects experience it in different stages of development including egg, nymphic, larval, and pupal. As a result of diapause, the normal growth pattern halts. Ecdysone, secreted by prothoracic glands, regulates metamorphosis and molting in insects and when the ecdysone is not produced, its absence suspends the insect?Ts development. During diapause, flies and mosquitoes find suitable, sheltered places to lessen their exposure to the cold. While in some insects diapause servers as a mechanism to escape environmental strains, in certain species of months and butterflies it is a natural par of the growth cycle. Some insects come out of diapause, when they find environmental factors agreeable. In some species of cutworms, nonetheless, diapause finishes when both favorable con***ions and sufficient time exist for the insect to respond to the new stimuli.
After delivery of a baby, animals such as kangaroos and other marsupials immediately mate again and then go through embryonic diapause, during which a newly-conceived embryo ceases to grow. In kangaroos, the new embryô?Ts development stops at the blastocyst stage when it is about 0.25 mm long and has approximately 100 cells. Not until the already delivered baby matures will the gestation of the second conclude its cycle. One of the species of marsupials common in North America is the Virginia Opossum, which is omnivorous and nocturnal.
8.8. When buying a house, you must be sure to have it checked for termites. A termites is much like an ant in its communal habits, although physically the two insects are distinct.
Like those of ants, termite colonies consist of different classes, each with its own particular job. The most perfectly formed termites, both male and female, make up the reproductive class. They have eyes, hard body walls, and fully developed wings. A pair of reproductive termites founds the colony. When new reproductive termites develop, they leave to form another colony. They use their wings only this one time and then break them off.
The worker termites are small, blind, and wingless, with soft bodies. They make up the majority of the colony and do all the work. Soldiers are eyeless and wingless but are larger than the workers and have hard heads and strong jaws and legs. They defend colony and are cared for by the workers.
The male and female of the reproductive class remain inside a closed-in cell where the female lays thousands of eggs. The workers place the eggs in cells and care for them. Even if one colony is treated with poison, if a male and female of the reproductive class escape, they can form a new colony.
Pest control companies can inspect a house for infestation of termites. Often, a lay person cannot spot the evidence, so it is critical to have the opinion of a profes-evidence, so it is critical to have the opinion of a professional. Treatments vary depending upon the type of termite.
8.9. The body of an adult insect is subdivided into a head, a thorax of three segments, and a segmented abdomen. Ordinarily, the thorax bears three pairs of legs. One or two pairs of wings may be attached to the thorax. Most adult insects have two large compound eyes, and two or three small simple eyes.
Features of the mouth parts are very helpful in classifying the many kinds of insects. A majority of insects have biting mouth parts of mandibles as in grasshoppers and beetles. Behind the mandibles are the maxillae, which serve to direct food into the mouth between the jaws. A labrum above and a labium below are similar to an upper and lower lip. In insects with sucking mouth parts, the mandibles, maxillae, labium, and labium are modified to provide a tube through which liquid can be drawn, In a butterfly or moth, the coiled drinking tube is called the proboscis. Composed chiefly or modified maxillae fitted together, the proboscis can be extended to reach nectar deep in a flower. In a mosquito or an aphid, mandibles and maxillae are modified to sharp styles with which the insect can drill through surfaces to reach juice. In a housefly, the expanding labium forms a spongelike mouth pad that in can use to stamp over the surface of food.
Được nguyenthanhchuong sửa chữa / chuyển vào 05:44 ngày 06/03/2004

TOEFL reading comp. without questions?


There can be miracles when you believeThough hope is frail, it's hard to killWho knows what miracle you can achieveWhen you believe... somehow you willYou will when you believe....

Great job NTC!
These are just preliminary reading before one gets to read the real stuff in college. Chew on these!!!