世界杯红牌 / 2026-08-21 05:36:39
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为什么树叶落地时大多背面朝上？
Why do most leaves land with their undersides up?
漫步秋日林间，你或许会发现一个有趣的现象：飘落的树叶大多背面朝上。这并非偶然，而是树叶自身的结构特性决定的。
When wandering through a forest in autumn, you may notice an interesting phenomenon: most falling leaves land with their undersides up. This is no coincidence, but rather determined by the structural characteristics of the leaves themselves.
树叶的正面和背面在构造上差异显著。叶片正面的栅栏组织排列紧密，细胞呈长柱形，含有更多叶绿素，负责高效吸收阳光进行光合作用，因此密度较大；而背面的海绵组织细胞排列疏松，间隙较多，密度相对较小。这种 “正面重、背面轻” 的重量分布，就像一个小小的 “不平衡体”。
There are significant structural differences between the upper and lower sides of a leaf. The palisade mesophyll on the upper side of the leaf is densely arranged, with elongated columnar cells containing more chlorophyll. Responsible for efficiently absorbing sunlight for photosynthesis, this layer has a relatively high density. In contrast, the spongy mesophyll on the lower side consists of loosely arranged cells with more intercellular spaces, resulting in a lower density. This weight distribution—"heavier on the upper side and lighter on the lower side"—makes the leaf like a tiny "unbalanced body".
当树叶从树上脱落，在空气中飘落时，受重力和空气阻力影响，较轻的背面会向上翻转，较重的正面则更容易朝下。同时，树叶边缘的形状和空气流动的细微变化，也会进一步促使背面朝上的姿态稳定下来。最终落地时，大多数树叶便自然呈现出背面朝上的状态，成为秋日里一道藏着科学奥秘的风景。
When a leaf detaches from the tree and falls through the air, it is affected by gravity and air resistance. The lighter lower side flips upward, while the heavier upper side tends to face downward. Additionally, the shape of the leaf's edges and subtle changes in air flow further help stabilize the posture of the leaf with its underside up. Eventually, when it lands, most leaves naturally end up with their undersides facing upward, becoming a scenic sight in autumn that holds a scientific mystery.
重要单词
1、phenomenon /fəˈnɒmɪnən/ (n.) 现象
2、structural /ˈstrʌktʃərəl/ (adj.) 结构上的
3、palisade /ˌpælɪˈseɪd/ (n.) 栅栏
4、mesophyll /ˈmezəfɪl/ (n.) 叶肉
5、chlorophyll /ˈklɒrəfɪl/ (n.) 叶绿素
6、photosynthesis /ˌfəʊtəʊˈsɪnθəsɪs/ (n.) 光合作用
7、density /ˈdensəti/ (n.) 密度
8、detach /dɪˈtætʃ/ (v.) 脱落，分离
9、resistance /rɪˈzɪstəns/ (n.) 阻力
10、stabilize /ˈsteɪbəlaɪz/ (v.) 使稳定返回搜狐，查看更多
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