假设你的窗台上有两株植物 – 一棵是仙人掌，另一棵是和平百合。你忘了给他们浇水几天，和平百合枯萎了。 （别担心，只要你发现这种情况就会加水，大部分时间它会恢复生命。）然而，你的仙人掌看起来和几天前一样清新健康。为什么有些植物比其他植物更耐受干旱？植物的耐旱性有几种作用机制，但是一组植物具有利用它的方式，使其能够生活在低水条件下，甚至生长在世界干旱地区，如沙漠。这些植物被称为Crassulacean酸代谢植物，或CAM植物。令人惊讶的是，超过5％的所有维管植物物种都使用CAM作为其光合作用途径，而其他物种则可能在需要时表现出CAM活性。 CAM不是替代生化变体，而是使某些植物能够在干旱地区生存的机制。事实上，它可能是一种生态适应。除上述仙人掌（仙人掌科）之外，CAM植物的实例是菠萝（凤梨科），龙舌兰（龙舌兰科），甚至一些天竺葵（天竺葵）。许多兰花是附生植物和CAM植物，因为它们依靠它们的气生根来吸收水分。
英国生物学Assignment代写：CAM活性
Suppose you have two plants on your window sill – one is a cactus and the other is a peace lily. You forgot to water them for a few days, and the peace lily withered. (Don’t worry, as long as you find this, it will add water, and most of the time it will return to life.) However, your cactus looks as fresh and healthy as it was a few days ago. Why are some plants more tolerant of drought than others? Plant drought tolerance has several mechanisms of action, but a group of plants have a way to use it to live in low water conditions, even in arid regions of the world, such as the desert. These plants are known as Crassulacean acid metabolizing plants, or CAM plants. Surprisingly, more than 5% of all vascular plant species use CAM as their photosynthesis pathway, while others may exhibit CAM activity when needed. CAM is not a substitute for biochemical variants, but a mechanism by which certain plants can survive in arid regions. In fact, it may be an ecological adaptation. In addition to the above cactus (Cactaceae), examples of CAM plants are pineapple (Bromeliad), agave (Agave), and even some geranium (geranium). Many orchids are epiphytes and CAM plants because they rely on their aerial roots to absorb water.