题目：
在下图所示的密闭暗箱里，放一盆生机盎然的绿色植物，烧杯中盛有蒸馏水，并悬浮着一个塑料小球，数天后，发现塑料小球漂浮在液面上，根据上述现象回答：
(1)烧杯中发生反应的化学方程式为 _____________________。
(2)塑料小球漂浮的原因是___________________。
答案：
(1)CO2+H2O==H2CO3
(2)绿色植物在黑暗处只有呼吸作用，呼出CO2，CO2与水反应生成碳酸，使溶液密度增大，溶液密度增大，小球漂浮到液面上
在下图所示的密闭暗箱里，放一盆生机盎然的绿色植物，烧杯中盛有蒸馏水，并悬浮着一个
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