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How Trees Move Water Upward Against Gravity
树木如何将水分逆重力向上输送？
精读先不看文字，完整听一遍。
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Trees lift water from roots to leaves through narrow xylem tubes — some over 100 meters tall — using cohesion, adhesion, and transpiration.树木通过狭窄的木质部导管将水分从根部输送到叶片——有些树木高达100多米——依靠内聚力、附着力和蒸腾作用。
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Water molecules stick tightly to each other (cohesion) and to xylem walls (adhesion), forming continuous columns under tension.水分子彼此紧密吸附（内聚力），也紧贴木质部管壁（附着力），在张力下形成连续水柱。
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As sunlight warms leaves, water evaporates through tiny pores called stomata — pulling more water upward like a chain being drawn.阳光加热叶片时，水分经气孔蒸发——像拉链条一样将更多水分向上牵引。
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This 'transpiration pull' creates negative pressure — sometimes stronger than a vacuum — yet the water column rarely breaks.这种‘蒸腾拉力’产生负压——有时强于真空——但水柱却极少断裂。
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Capillary action helps in small stems, but it alone cannot explain movement in tall trees; transpiration is the dominant force.毛细作用在幼茎中起辅助作用，但无法单独解释高大树木中的水分运输；蒸腾作用才是主导力量。
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On hot, dry days, transpiration rates soar, increasing water flow — unless drought triggers stomatal closure to conserve moisture.在炎热干燥的天气里，蒸腾速率急剧上升，加快水分流动——除非干旱导致气孔关闭以保水。
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Xylem sap contains minerals absorbed from soil, delivering nutrients essential for photosynthesis and growth.木质部汁液含从土壤吸收的矿物质，为光合作用和生长提供必需养分。
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Climate change intensifies drought stress, disrupting this system and contributing to widespread forest dieback worldwide.气候变化加剧干旱胁迫，扰乱这一系统，导致全球范围森林大面积死亡。
精读 · 大约 10 分钟
听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。
③ 学 · 重点表达
- Xylem sap contains minerals absorbed from soil, delivering nutrients essential for photosynthesis and growth. 木质部汁液含从土壤吸收的矿物质，为光合作用和生长提供必需养分。
- Climate change intensifies drought stress, disrupting this system and contributing to widespread forest dieback worldwide. 气候变化加剧干旱胁迫，扰乱这一系统，导致全球范围森林大面积死亡。
- Trees lift water from roots to leaves through narrow xylem tubes — some over 100 meters tall — using cohesion, adhesion, and transpiration. 树木通过狭窄的木质部导管将水分从根部输送到叶片——有些树木高达100多米——依靠内聚力、附着力和蒸腾作用。
④ 懂 · 选一选
⑤ 今天会说这一句
Xylem sap contains minerals absorbed from soil, delivering nutrients essential for photosynthesis and growth.
⑥ 跟读并录音
Xylem sap contains minerals absorbed from soil, delivering nutrients essential for photosynthesis and growth.
第一版：录下来、回听、再听标准音。系统打分以后再加。
⑦ 说 · 自己来一句
用今天的表达，自己说一句。
例子：Xylem sap contains minerals absorbed from soil, delivering nutrients essential for photosynthesis and growth.
已记下。连续天数以后会显示在课表里。
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