问题 探究题

将盆栽银边天竺葵(其叶边缘无叶绿素,为白色)放在黑暗处一昼夜后,用黑圆纸片将其中一片叶片的“B”处两面遮盖(如图所示),放在阳光下照射数小时后,将此叶片摘下,在酒精中隔水加热后取出,滴加碘液进行观察。请参看图并回答问题。

(1)实验前将天竺葵放在黑暗处一昼夜的目的是:将叶片内原有的           消耗掉,避免对最终的实验现象产生干扰。

(2)C处变蓝色,证明光合作用的产物是       。A处不变色,原因是           。被遮光的B处会变色吗?

答:       。原因是                       

(3)请把光合作用的反应式补充完整:

答案

(1)有机物(或淀粉、营养) 

(2)淀粉   无叶绿素(或无叶绿体)   不变色    绿叶在光下才能产生淀粉(或淀粉的产生需要光、光合作用需要在光下才能产生淀粉等,无“淀粉”字眼不得分)           

(3)二氧化碳   氧气

题目分析:实验步骤:暗处理→部分光照→光照→摘下叶片→酒精脱色→漂洗加碘→观察颜色。

(1)暗处理:将盆栽的天竺葵放到黑暗处一昼夜,目的是把叶片中的淀粉全部转运和消耗,这样就说明了,实验中用碘液检验的淀粉只可能是叶片在实验过程中制造的,而不能是叶片在实验前贮存。

(2)叶的银边部分A和绿色部分C形成一组对照实验,变量是叶绿体,A处不变色,说明没有产生淀粉,即没有进行光合作用,由此证明光合作用的场所是叶绿体,叶的遮光部分B和见光部分C形成一组对照实验,变量是光,B处遮光而没有产生淀粉,说明缺少光照是不能进行光合作用的。

(3)绿色植物通过叶绿体利用光能把二氧化碳和水合成有机物,并储存能量,同时释放出氧气的过程叫光合作用,所以即可写出表达式。

点评:此题考查绿叶在光下制造有机物(淀粉)的实验,难度一般,解题的要点:光是制造有机物的必要条件,光合作用制造淀粉。

问答题
听力题

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