Now, every single cell inside our body contains this cell membrane and all these cell membranes have the same properties. So let's examine what these properties are. Property number one is these cell membranes are relatively thin and they enclose that entire cell. They create a closed boundary. Now, the fact that the cell membranes are thin basically means they only consist of two layers of molecules, two layers of lipids, as we'll see in a future lecture. Now, on top of that, inside the cell, inside eukaryotic cells, which are cells found inside our body, we also have individual organelles that themselves contain membrane.