十万个为什么·科学阅读30篇（9）

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为什么树叶在秋季变色——而不仅仅是在秋天？

Chlorophyll gives leaves their green color and breaks down sunlight for photosynthesis all spring and summer.
As days shorten and temperatures drop, trees seal off veins that carry nutrients to and from leaves.
With chlorophyll production halted, other pigments like yellow carotenoids and red anthocyanins become visible.
Anthocyanins aren’t present all year—they’re newly made in autumn when sugars get trapped in leaves.
Soil moisture, light intensity, and sudden cold snaps influence how vivid the colors become.
Maple trees produce more anthocyanin in sunny, cool autumn days than in cloudy or warm ones.
Evergreen trees avoid this process by keeping needle-like leaves for several years with slower nutrient loss.
Some tropical trees shed leaves during dry seasons instead of winter, showing similar pigment shifts.
Color change is not about temperature alone but about photoperiod-triggered hormonal signals.
It’s nature’s way of recycling nutrients before winter makes photosynthesis impossible.

听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。

It’s nature’s way of recycling nutrients before winter makes photosynthesis impossible. 这是大自然在冬季光合作用无法进行前回收养分的方式。
Color change is not about temperature alone but about photoperiod-triggered hormonal signals. 叶色变化不仅取决于温度，更由日照长度触发的激素信号调控。
With chlorophyll production halted, other pigments like yellow carotenoids and red anthocyanins become visible. 叶绿素停止生成后，原本被掩盖的黄色类胡萝卜素和红色花青素便显现出来。

这篇中文题目最接近哪一句？为什么树叶在秋季变色——而不仅仅是在秋天？一次学校运动会的通知一份超市购物清单

课文第一句的意思更接近？叶绿素赋予叶片绿色，并在春夏两季将阳光分解用于光合作用。今天学校放假了。请把窗户打开。

这一课主要在讲什么？（看英文标题） Why Leaves Change Color in Autumn — Not Just in Fall How to cook noodles A maths worksheet

It’s nature’s way of recycling nutrients before winter makes photosynthesis impossible.

It’s nature’s way of recycling nutrients before winter makes photosynthesis impossible.

第一版：录下来、回听、再听标准音。系统打分以后再加。

用今天的表达，自己说一句。

例子：It’s nature’s way of recycling nutrients before winter makes photosynthesis impossible.