托福真题：11015年10月托福阅读全真试题-托福真题.docx

托福真题：11015年10月托福阅读全真试题-托福真题
托福真题：11015年10月托福阅读全真试题-托福真题
11015年10月托福阅读全真试题
Questions 1-13
Atmosphe
very small bore, the forces of cohesion (the attraction between water molecules) are so great that the strength of a column
托福真题：11015年10月托福阅读全真试题-托福真题
11015年10月托福阅读全真试题
Questions 1-13
Atmospheric pressure can support a column of water up to
10 meters high. But plants can move water much higher, the
sequoia tree can pump water to its very top, more than 101
meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants
was a mystery. Some botanists hypothesized that the living
cells of plants acted as pumps, But many experiments demonstrated that the stems of plants in which all the cells are killed
can still move water to appreciable heights. Other explanations
for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of


the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers,
which are among the tallest trees, have unusually low root pressures.
If water is not pumped to the top of a tall tree, and if it
i