 This final video is going to look at a little bit around the importance of buffers in natural systems. And it's good for you to have a number of different examples that you can use in order to describe and apply the use of buffers to different natural systems. So one natural system that we can talk about is human blood. The pH of human blood is usually around about 7.4. But one of the important things that's happening to blood is the rise and fall of carbon dioxide levels. Now even if you don't study biology as well as chemistry, you would know I'm sure from your junior days that carbon dioxide is a very important byproduct of respiration. It is something that is produced in all of the body's cells because it is part of the process of producing energy. It's also exchanged in the lungs so that the carbon dioxide leaves the body through the diffusion across the walls of the alveoli and leaves every time we exhale. So there are places in the body where the concentration of carbon dioxide is higher and there is a diffusion gradient created as the carbon dioxide moves from a place of high concentration to lower concentration. And the same thing there are places in the body where the concentration of carbon dioxide is quite low. The problem with carbon dioxide is that when it interacts with the liquid part of the blood, the plasma, there's a lot of water in there and therefore we can actually get weak carbonic acid. This acid here is a product of the reaction between carbon dioxide and water. Of course the other thing that we know about carbonic acid and also carbon dioxide and water is that we have an interaction which involves hydrogen ions or protons. So what we have here is the carbonic acid and the second of the reactions that you can see is the carbonic acid which is a weak acid and it's in equilibrium with hydronium ions or protons and the hydrogen carbonate, sometimes referred to as the bicarbonate ion. So this is well fine and good but what's the actual consequence of all of this? Well the problem is that increasing carbon dioxide, so if we have an increase in carbon dioxide then what's going to happen is that the equilibrium is going to shift to try and use that by using that it's going to push it in this direction which is going to increase the concentration of the hydrogen ions and therefore it's going to make the pH 4. Whilst we're looking for a goal of around 7.4, if it starts to fall below 7.4, we start to call it a condition known as acidosis. And beyond about 6.8 there are very serious consequences including potential death as a result of this fall of pH in the blood. So whilst there is an optimal pH there is also a range beyond which the body system just cannot cope. And likewise if we talk about drops in carbon dioxide then the shift may occur in the opposite direction, the concentration of H plus ions will fall and therefore we'll get a condition known as alkalosis which is too high a pH and as it rises up into these higher values it becomes just equally as much of a problem. So therefore it's very important that we have this buffer in the blood to try and ensure that any changes that are occurring are counted so that we can try and maintain a stable pH.