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Plant adaptation to the desert(背景材料)
Cactus
The secret to the superior endurance of cacti lies in their Over millions of years, through natural selection, only the strongest and best adapted species
As you know, it is very dry in the Plants that adapt to this are known as xerophytes (from zeros, dry and python, plant). There are plants that avoid the dry season by sprouting from seed just after the spring rain andgrowing very fast so that by the time the dry season comes, they have already produced a lot of seeds and These seeds lie on the soil for the dry season and sprout again in spring and the cycle Other xerophytes simply droptheir leaves and stay dormant for the But there is another special type of xerophytes which stores water in its fleshy Such plants are called succulents (from success, juicy). The cactus is a typical example of
If you cut a cactus open, you see a juicy, slimy This is where the moisture is stored for the dry The part between the middle circle (and pith) and just under the very green part of the plant (or palisade parenchyma)just under the skin is allocated for the storage of water and food for the This is a type of spongy parenchyma and can take up to 85% of the plant's This is a major adaptation in the Because the plant remainscompletely alive during the dry season and there is no need for it to dry up and lose everything, makes it possible for the plant to grow to large Another advantage is that the plant retains supplies (in the form of starch) forthe winter so that it can flower right away in spring without accumulating more supplies (as most plants need to do in spring). The whole purpose of storing supplies for the winter is mostly to energize flowering in spring but it alsolets the cactus start growing much
Flowering plants breathe and transpire (evaporate water from their surface) through closeable microscopic pores called stoats on the leaves or To do this, their pores have to be In most plants these are open all day andon warm But for cacti this is inconvenient as in daytime it is very hot and thus the plant would lose a lot of water through So the cactus must close them in the But then it cannot breathe or photosynthesize(the process where sugars are made from carbon dioxide and water and releasing oxygen using the sun's energy). Succulents have an adaptation to Their stoats are closed during the day and are open at night, when it is not that hotand store carbon dioxide in its tissues as crass lean acid and then turn it back to carbon dioxide in the This process is called crass lean acid metabolism or CAM and it is a very smart way of respiring in the
If we look at the outside of the plant, we notice that there is a tough leathery skin covering the plant, we can also notice the presence of ribs and spines and sometimes These are all very smart They serve mainlyfor surviving heat but are also used as
The tough leathery skin is very impermeable to water, thus reducing evaporation from the surface of the This skin often has a layer of plant wax on it which is often lightly colored (Pilosocereus azures is an example of aplant with such wax), white or This reflects light and also reduces evaporation from the
