In this video we're looking at specialised exchange surfaces, and although we'll mention a few examples, the aim of this video is to explain the main features that they have in common. If we start with what they are, specialised exchange surfaces are just the parts of an organism over which they exchange substances with their environment. So if we look at a human first.
The main specialized exchange surfaces are the alveoli and the villi. The alveoli are small sac-like things that are found in the lungs, at the very ends of the bronchioles. And their job is to exchange oxygen and carbon dioxide between the air and the blood. So they're an exchange surface, because they exchange gases between the inside and outside of our bodies. Meanwhile, villi...
are these finger-like things that are found on the inside lining of the small intestines, and their role is to help us absorb nutrients like glucose and amino acids. If we consider plants instead now, these are also large multicellular organisms, and so they also need to have specialised exchange surfaces. For example, they have root hair cells, which help them to absorb water and mineral ions from the soil, and leaves which help them to absorb the carbon dioxide they need from the air. So as you can hopefully see by now, there are lots of different types of specialized exchange surfaces, and they're all a bit different.
However, there are a few common features that nearly all of them share, and you need to know what these are. The first is a large surface area. Having a really big surface area means that lots of molecules can diffuse across at the same time and so overall the rate of diffusion is higher.
For example, by having hundreds of millions of alveoli there's a huge area over which we can absorb the oxygen molecules that we need. This is also why villi have this long thin shape, why leaves are large and flat, and why root hair cells have these long, thin projections. The second common feature is that the surfaces themselves are usually very thin, and this means that there's only a short distance for substances to diffuse across.
For example, in root hair cells, water only has to diffuse across a thin cell wall and cell membrane to get into the plant. We often refer to this as a short diffusion distance. And it's important because it means that diffusion can take place more quickly. A third point is that the exchange surfaces are permeable to the substances that they need to exchange.
This just means that these surfaces allow the substances to diffuse across, rather than blocking them. If we look at just animal exchange surfaces now, another really important feature is a good blood supply. as this helps maintain a concentration gradient.
For example, having a good supply of blood to your villi means that as soon as some of the glucose is absorbed into the blood, that blood will quickly be taken away and replaced with blood that doesn't yet have lots of glucose in it. This helps maintain a concentration gradient between the lumen of the intestines and the bloodstream, so that more glucose can continue to diffuse down its concentration gradient into the blood. The last feature is a good supply of the external medium. This is kind of a tricky one to explain, but think of it as the air in the case of the alveoli, or food in the case of the villi, basically the stuff outside of our bloodstream. For example, if you want to absorb a lot of oxygen, you're going to need a good supply of air into your alveoli.
which is why you have to breathe in and out all the time. This also helps to maintain the concentration gradient because it means that we always have a high concentration of oxygen in our alveoli and so there's always a concentration gradient between the alveoli and the blood. So to quickly recap, the five main features of specialized exchange surfaces are that they have a large surface area, The surfaces are very thin.
The surfaces are permeable to whichever substances they need to exchange. There's a good supply of blood, which is sometimes called a good supply of internal medium. And there's a good supply of the external medium, for example, the air. Hey everyone, Amadeus here.
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