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¡¡¡¡Directions:

¡¡¡¡In the following article, some sentences have been removed. For Questions 41¡«45, choose the most suitable one from the list A¡«G to fit into each of the numbered blanks. There are two extra choices which do not fit in any of the gaps. Mark your answers on ANSWER SHEET 1. (10 points)

¡¡¡¡Fewer than 1% of the world¡¯s 265 000 flowering plants, most of which inhabit tropical regions, have been tested for their effectiveness against disease. ¡°We haven¡¯t even scratched the surface-not even in our own backyard,¡± says Jim Miller, director of the Missouri Botanical Garden¡¯s natural-products program. 41) .

¡¡¡¡Morphine, for example, is derived from poppies and medicines such as vincristine and vinblastine, isolated from the rosy periwinke, help treat cancers, including Hodgkin¡¯s disease and some leukemias. Curare, taken from several poisonous Amazonian plants and often used in the tips of hunting arrows, is used in drugs that cause anesthesia, and reserpine, an extract of the snakeroot plant, traditionally used in Asia to counteract poisonous snake bites, is the basis of several drugs to reduce anxiety and abnormally high blood pressure.

¡¡¡¡42) . Human activity, from farming to logging and road building, is making this band ever narrower, driving numerous species to extinction even before they have been discovered. ¡°I see ethnobotany-the study of the relationship between people and plants-as the key to the preservation of this vast collection of species as well as a pathway to halting many diseases,¡± says Paul Alan Cox, botany professor at Brigham Young University in Utah.

¡¡¡¡43£© . Pharmacologists must analyze between 10 000 and 17 000 chemical compounds before finding one with the potential to be tested for efficacy in humans. Until recently, animal testing and clinical trials of a singe drug required an average 12 years of research and cost up to 300 million dollars. But initial screening can now be done in a matter of days without using animals. Molecular biologists are able to isolate enzymes that can trigger human diseases, then expose those enzymes to a plant¡¯s chemical compounds. If a plant extract blocks the action of a particular enzyme-say, one that causes a skin disease-they know the plant has drug potential. By extracting specific chemicals from the leaves, roots or bark in a series of experiments and testing each sample individually, scientists can determine which of the plant¡¯s thousands of compounds actually blocks the enzyme.

¡¡¡¡44) . Some work with a handful of ethnobotanists like Cox to search out drug candidates based on their knowledge of native peoples; others use a broader approach, massª²collecting plants whose chemical compounds might contribute to new drugs.

¡¡¡¡45) . ¡°Native people have been testing plants on people for thousands of years,¡± he says. Through field research, Cox recently discovered that Homalanthus nutans-a rainª²forest tree whose bark has been used for centuries as a cure for hepatitis-contained a compound which appeared to inhibit growth of the AIDS virus and which is now undergoing further testing for possible use in the future.

¡¡¡¡£ÛA£Ý The drive to collect and screen more natural products for their medicinal effects is intensifying and this is good news for biologists and environmentalists concerned about the dwindling of the planet¡¯s biodiversity, mostly concentrated in a wide band around the equator.

¡¡¡¡£ÛB£Ý Major technological advances in screening processes have helped Cox and other ethnobotanists considerably.

¡¡¡¡£ÛC£Ý Yet nearly a quarter of prescription drugs sold in the U.S. are based on chemicals from just 40 plant species.

¡¡¡¡£ÛD£Ý Cox has located three other medically promising plants. Two of the plants, used by the natives to control skin diseases, are being investigated by a drug company. The third doubles the life span of infectionª²fighting T lymphocytes in the test tube; its effect in the human body is not yet known.

¡¡¡¡£ÛE£Ý As a result of these advances, about 100 U.S. companies are searching out plants. Drug companies and scientific institutions are working together on field research all over the world, racing to study as many natural substances as possible before they, or the native people who use them, disappear.

¡¡¡¡£ÛF£Ý Cox knows that if the rainª²forests continue to disappear, hundreds of potential drugs hidden there may never be found.

¡¡¡¡£ÛG£Ý Cox believes that field research provides a much better organized way of locating plants that have medical potential than random mass collecting.