hello biologists and today we are looking at 2.1.5 biological membranes taken from the ocr specification a and we're looking at specification point a today the rules of membranes within the cells and also the cell surface and you can see some of these rules listed here before you i'm going to talk through and go through each one of these points identifying what the matte scheme wants you to know about each of these points and you'll find that within the red box which are on the slides so the first thing we're going to look at is these partially permeable barriers between the cell and its environment and as you can see on the diagram there you can see those blue molecules there starting at the outside of the cell and over time you can see these blue molecules entering into the cell and this is basically demonstrating to you that this the plasma or cell surface membrane allows the passage or transfer of substances in and out of the cell it acts a bit like a bouncer in a club determining who's going to come in and out and you look at um the different parts and the different ways in which molecules can move in and out of cells later on in the membranes topic where you look at osmosis active transport facilitator diffusion and diffusion in more detail but for now i've put on there a couple of examples for you to take a look at we also need to look at the partial permeable barriers between organelles and the cytoplasm and as you can see here there's some key terminology here that the masking really wants you to know it's really important that we have compartmentalization within our organelles that separate the contents of our organelles from the cytoplasm for example if you take the lysosome which you've met in cell structure in a lysosome we have hydrolytic enzymes and they need to be kept separate from all the organelles otherwise these hydrolic hydrolytic enzymes are going to break down and hydrolyze other components within the cell which we really do not want to happen these membranes surround organelles they also allow and control what enters and leaves that organelle we need to know about the role of of membranes within organelles too and as you can see here i've used the example of a mitochondria there are other examples you can use as well but for example in the mitochondria the membrane here the inner membrane allows for the concentration gradient to be established and maintained you'll learn a lot more about that when you hit respiration at a2 but also um as you can see in here you could you've got atp synthase which is an enzyme which is embedded in the membrane here um again you'll learn about this later on when you've got onto respiration in a lot more detail so we've done that power points that we've done that point there in in green there as you can see the other point that you need to know here in terms of from the mark scheme is that membranes can be a site of chemical reactions which again do take place within the mitochondria but you'll learn about that in a lot of detail later on at a2 for now all we need to know is that a membrane can be a site of chemical reaction so the last little bit on the specification point we need to be aware of is this last one here about the site of cell communication and cell signaling so cell signaling is really important because cells need to communicate with each other and use signals such as hormones in order to do so they need to detect the signals they need to detect these hormones and they need sensors or better word for a receptor on the cell surface and each of these hormones that i use have a specific and complementary receptor on the cell surface membrane the definition of cell signaling that you need to know is that cell signaling is communication between cells it is cell cell recognition and identification it is where cells work together to trigger a response inside that cell now that response inside that cell will depend upon what that hormone is that is being used and there are a couple of examples here that follow on just to help and aid your understanding here so in your exam they may give you a hormone or a drug that you've never heard of before in your life and you have to apply what you know about cell membranes about receptors and about cell communication and cell signaling to that hormone or drug so here is one example from insulin i'm not going to read that out but that is one example that you may be given and another example here is a medicinal drug beta blockers again the main thing here is being able to apply your knowledge of membranes and of receptors and of cell signaling to these unfamiliar contexts guys as ever with within your exam remember do not use the words it's they amount or size use good scientific terminology to help you get as many marks as you possibly can and good luck