Lecturer : In today’s lecture, I’m going to continue our work on plants and talk about plants that live in the desert. Now, just a bit of background information first. As you know, about 1/3 of the world is covered in desert, and the sort of area they’re found in is important. Does it usually created because the area of land where they lie is located in something that’s called a Q31 rain shadow?
Now this is a region that’s beneath a mountain range, and what happens is that the wind blows over the mountains towards the area. But as it does so, the air loses its moisture and becomes very dry. Because of this down wind location, rainfall often totals just a Q32 few inches a year, or in some regions there’s absolutely none, and you can imagine the effect of this. It means that whatever rain does fall evaporates quickly from the ground, and that makes the soil salty and also leaves behind a whole range of other Q33 minerals as well.
Now, despite this, desserts are home to many living things, in fact, there second only to tropical rainforests in the variety of plant and animal species that live there. So how do plants grow in a place that’s so dry? Well, their specially adapted to do this? In fact, many of the fascinating features of desert plants are adaptations. These are traits that helped the plants survive in its harsh environment, and desert plants have two main adaptations. The first is that they have an ability to Q34 collect water and to store it. Some have large root systems and amazing internal water storage systems.
The second adaptation is that they have features that can actually reduce water loss, and these are often very special leaf designs or additions to the plant’s structure. So let’s have a look at some examples. Desert plants often look very different from any other plants. Okay, This 1st 1 is the Saguaro Cactus, which grows in North America. It looks a bit like an open hand with long fingers. This plant has a large network of roots that extend far, far away from its trunk, and these roots collect water after rain. Then the waters taken here to the green Q35 stem. This is where all its water is kept, and it keeps the whole plant alive until the next rain comes. It’s a pretty woody plant. In fact, its skeleton is actually used in building materials, so it’s quite strong. This next plant is called the barrel cactus, named because it does look rather like a barrel. It can grow up to a meter in height, which is pretty big, and it has long yellow spines. Now this plant has an interesting adaptation because its shape allows it to Q36 expand when it rains, hence the barrel and store water in its spongy tissue. But then it shrinks in size during dry times as it uses the stored water. So that’s a clever design.
The third cactus, often just one plant reaching upwards, has these Q37 white hairs all over its surface. It’s called the old man cactus because of the white hairs, and these help the plant reflect the hot desert sun. So this adaptation is, Ah, water conservation aid, if you like. Another adaptation, not directly connected with water but with survival, is found on something like the prickly pear cactus. There are hundreds of these in the Mexican desert. I’m sure you’ve seen them on films and adverts. Um, Yes, so because desert plants store water in their spongy tissue, animals will eat them. So the plant has sharp Q38 thorns specially designed to prevent the predator from being able to well get near it a tool. Our next plant is called the desert Spoon. This plant has long leaves that fan out, and they’re very succulent because they can also store water inside. However, there also usually very Q39 tough, and this helps keep the water inside and also makes from less tasty.
Finally, we come to the aloe plant. This is one that many people keep in their homes. It’s an attractive plant, which has leaves that look and feel rather waxy. This surface behaves in a similar way, toe a Q40 plastic wrapper and helps the plant to hold the water in. It’s a wonder plant, this one. It’s juice has been used as a medicine for centuries, and even today you can find it in products on the pharmacists shelves or in creams and lotions. Okay, well, we’re going to take a closer look.