题型：阅读理解 题类：常考题 难易度：普通
河南省信阳市2020-2021学年高二上学期英语期中教学质量检测试卷
New research into a long-lived tree has shown some of the tricks that have helped it survive for thousands of years. The ginkgo(银杏树) is a huge, slow-growing tree with fan-shaped leaves, native to China, but planted in parks and gardens across the world. Some of the largest ginkgoes are said to be more than 3, 000 years old.
In order to discover how these and other trees can live for so long, scientists from the US and China studied 34 healthy ginkgoes of different ages. The team studied growth rings in each tree's trunk(树干), as well as cells(细胞) from the bark, leaves and seeds. They found that 600-year-old trees were just as healthy as 2-year-olds.
To learn more, the team then looked in detail at the DNA of nine trees aged between three and 667 years old. DNA is the chemical in the cells of plants and animals that holds instructions that tell any living thing how to grow and develop-including what to do at different times in its life At the beginning of a tree's life, DNA instructs the cells in a seedling to divide quickly so the tree grows rapidly. The cells also make special chemicals to help the young plant survive difficult situations, such as disease. As most trees grow older, their DNA tells their cells to divide more slowly (so growth slows down) and to make fewer chemical defenses(防御).
Ginkgoes, however, do things differently. The team found that although their growth finally slows, both young and old trees make protective chemicals." The secret is keeping a really healthy defense system," said researcher Richard Dixon." As ginkgoes age, they show no sign of weakening their ability to defend themselves from things like disease. "Other trees that live for a long time may have the same ability.
For all their defenses, though, ginkgoes cannot live forever--they finally meet with deadly accidents such as fire, disease and storms. While they last, however, these leafy trees are some of the most beautiful trees in the world.
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