 Hi there, my name is Sarah Rottet. I'm a researcher at the Austrian National University. In my work I'm interested in how molecules go through the cell membrane and more specifically we are interested, we are trying to make plants better at taking in more carbon dioxide. The goal is to make crops that can grow better and faster to help feed the world population and if you want to know a bit more about the right project you can just click on the link below. Today we are going to talk about what is the cell membrane. Every living organism is composed of individual cells and each of them are surrounded by double layer of lipid, the cell membrane. Basically it keeps everything together and also it protects the cell from the environment surrounding it. If you think about it we humans like to do the same. We create rooms or buildings to separate our activities. For instance here is my lab and it's surrounded by a wall because it's very important for us to control its temperature, air quality, to contain nasty chemicals and biological hazards and to make sure only authorized people can go inside. In some ways it's very similar to what's going on at the cell membrane and we call that semi-permeable. Basically the cell membrane helps to regulate what's going in and out of the cell but we will talk about that a bit later in the next videos. For now let's have a closer look at this membrane structure. It contains various proteins, cholesterol, but the most abundant element are the phospholipids. Unlike other lipids which hates water, think about olive oil that can't be mixed with water. Phospholipids are amphiphilic molecules which means they like and dislike water at the same time. It sounds like a very complicated relationship right? But the secret lies in their internal structure and the way they interact with each other. So let me explain. A phospholipid contains a phosphate head which is hydrophilic. Hydro means water, philic means love. So that's the part that loves water. But it also contains a tail made of fatty acids and glycerol and that's a hydrophobic tail and phobic means hate. And this spatial separation allows the phospholipid to assemble into a big structure which is called the phospholipid bilayer where heads are facing out where the water is, while the tails are facing each other in the middle excluding water molecule. So in conclusion the phospholipid bilayer is the skeleton of a cell membrane.