(PUC-Rio -2004)Text 1The widespread destruction of

(PUC-Rio - 2004)

Text 1

The widespread destruction of tropical rainforest ecosystems and the consequent extinction of numerous plant and animal species is happening before we know even the most basic facts about what we are losing.

Covering only 6 percent of the Earth's surface, tropical moist forests contain at least half of all species. The 6abundant botanical resources of tropical forests have already provided substantial medical advances; yet only 1 percent of the known plant and animal species have been carefully examined for their medicinal potentials. Meanwhile, 2 percent of the world's rainforests are irreparably damaged each year. Scientists estimate that, at the accelerating rate at which rainforests are now being destroyed, as much as 20 or 25 percent of the world's plant species will soon be 7extinct.

1Approximately 7,000 medical compounds prescribed by Western doctors are obtained from plants. These drugs had an estimated retail value of US$ 43 billion some years ago. Seventy percent of the 3,000 plants identified by the United States National Cancer Institute as having potential anti-cancer properties are characteristic of the rainforest. Tropical forest species serve Western surgery and internal medicine in three ways. First, extracts from organisms can be used directly as drugs. 2For maladies ranging from persistent headaches to 8lethal contagions such as malaria, rainforest 9medicines have provided modern society with a variety of cures and pain relievers.

Secondly, chemical structures of forest organisms sometimes serve as models from which scientists and researchers can chemically synthesize drug compounds. For example, the blueprint for aspirin comes from extracts of willow trees found in the rainforest. Neostigmine, a chemical obtained from the Calabar bean and used to treat glaucoma in West Africa, also provides the blueprint for synthetic insecticides. However, the chemical structures of most natural drugs are very complex, and simple extraction is usually less expensive than synthesis. 3Ninety percent of the prescription drugs that are based on higher plants include direct extractions from plants.

Finally, rainforest plants provide aids for research. 4Certain plant compounds enable scientists to understand how cancer cells grow, while others serve as testing agents for potentially harmful food and drug products. Tropical forests offer hope for safer contraceptives for both women and men. The exponential growth of world population clearly demonstrates the need for more reliable and effective birth control methods. Worldwide, approximately 4,000 plant species have been shown to offer contraceptive possibilities. The rainforest also holds secrets for safer pesticides for farmers. 5Two species of potatoes have leaves that produce a sticky substance that traps and kills predatory insects. This natural self-defense mechanism could potentially 10reduce the need for using pesticides on potatoes. Who knows what other tricks the rainforest might have up its leaves?

http://www.ran.org/info_center/factsheets/05f.html 1995-2003 Rainforest Action Network

Mark the only sentence that CANNOT be correctly completed with the preposition FROM.