💨 蒸腾作用：树叶的“抽水机”💨 Transpiration: the Leaf's Water Pump
上一片里，小苗破土站稳，根开始大口喝水。可十几米高的大树，水怎么爬上树梢？答案藏在叶子上无数扇会开关的“小门”里。Last leaf, the seedling stood up and its roots began drinking. But in a tree over ten meters tall, how does water climb to the crown? The answer hides in thousands of tiny doors on the leaves that open and shut.
第 1 步：给植物套个塑料袋Step 1: Put a plastic bag over a plant
说叶子在“跑水”，拿什么证明？做个小实验。Leaves “leak water”? Prove it with a tiny experiment.
给盆栽套一个塑料袋，扎好领口，放一晚上：内壁挂满小水珠。土是封住的，水珠只能来自叶子——叶背的气孔把体内的水变成水蒸气散出去。水以水蒸气的形式从气孔跑掉，这就是蒸腾作用。Bag a potted plant, tie the neck, leave it overnight: the inside coats over with droplets. The soil is sealed, so the water can only come from the leaves — the stomata on the leaf's underside let the plant's water out as vapor. Water leaving as vapor through stomata: that is transpiration.
叶子散掉水汽，怎么反而帮了大树的忙？Losing vapor — how does that help a tall tree?
第 2 步：从根到梢的拉力链Step 2: The pull chain from root to crown
茎里的导管是一条灌满水的细管，从根直通叶。叶子一散水汽，管口的水就被往上拽，整条水柱像拔河一样被拉起来，根趁机补水——这股力叫蒸腾拉力。它比水泵还可靠：再高的大树，树梢的叶子也能“抽”到水。Inside the stem, vessels are thin tubes full of water, root to leaf. As leaves release vapor, the water at the top gets tugged upward, and the whole column rises like a tug-of-war rope while the roots refill it. This force is the transpiration pull — more reliable than any pump: even the tallest tree's crown gets its drink.
可水一直往外跑，植物就不怕渴吗？But if water keeps escaping, won't the plant go thirsty?
第 3 步：会看门的小气孔Step 3: The little doors that mind the shop
气孔由一对保卫细胞把守，能开能关：清晨凉润，门大开，痛快干活（顺便带走热量给叶子降温）；烈日正午，失水太快，门关小、省水保命。园丁移栽花苗时剪掉部分叶子、遮阴喷雾，也是同一招——降低蒸腾，让根还没扎稳的苗少失水。Stomata are guarded by a pair of cells that open and shut: on cool moist mornings, doors wide open, work in comfort (the evaporating water cools the leaf); under blazing noon sun, they narrow to save water. Gardeners do the same when transplanting — trim some leaves, shade, mist — cutting transpiration while the roots are still shaky.
🎮 蒸腾拉力实验室（30 秒）🎮 Your turn: the transpiration lab (30 seconds)
实验台上有盆罩了塑料袋的植物：调湿度、开关风扇，看蒸腾速度怎么变，再完成 4 关任务。A bagged plant waits on the bench: tune humidity, toggle the fan, watch the rate, then clear 4 levels.
一句话记住它：蒸腾 = 叶子用气孔散水汽，顺手把整棵树的水往上抽。Remember it in one line: transpiration = leaves venting vapor through stomata, hauling the whole tree's water upward as they do.
蒸腾：水以水蒸气从叶背气孔散失（塑料袋实验可证明）Transpiration: water escapes as vapor through stomata (proved by the plastic-bag experiment)蒸腾拉力：叶散水汽→水柱上抽→根水补充，几十米大树也够得着；水分蒸发还给叶子降温Transpiration pull: vapor out, column up, roots refill — tall enough for any tree; evaporation cools the leaf too正午气孔关小省水；移栽剪叶遮阴，降蒸腾保苗Noon: stomata narrow to save water; transplanting trims and shades to cut transpiration
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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