hello biologists today we're going to be looking at the experiments linked into the factors affecting the membrane permeability this is taken from the ocr specification for a level biology looking at biological membranes 2.1.5 now the most popular experiment here that you will find linked into this specification point is one on b root and in this investigation what happens is the scientists will take samples of an uncooked beetroot and place them into water at different temperatures now what you will then do is compare the color change on in this water so there's a couple of things that you need to think about here before we start the investigation and that is what factors and what variables are we going to be controlling okay so this part here is a very popular exam question it's taken directly from the mark scheme these points on this right hand side we need to be making sure we're keeping the mass and the length of the b beetroot the same all of our beetroot pieces will have the same math and the same length it's really important here you do not say size size will get you no marks at all we're also going to be using the same species of beetroot ideally the same beet root really we're going to be using the same volume of water and also all of our beetroot cylinders will be in the water for exactly the same length of time one thing to note as well which they really like asking in this experiment is after i've cut the cylinders off my beetroots and measured them made sure they're all the same length and or mass i must make sure that i dry my beetroot samples before i put them into the water and this is because during the cutting process you will have damaged some of the membrane so some of the pigment will have leaked out it's important that you remove this excess pigment because you do not want it to impact on your results you want to have com results that you can compare to each other and that haven't been distorted somehow we need to make sure our results are reliable okay so as you can see here now what i'm going to start to do is increase this temperature and have a look what happens to the the color changing in the water as the temperature increases okay so hopefully you notice there that as the temperature increases the the color change gets more darker so the color becomes a lot more darker now if you're just going off color changes that is qualitative and this is not very good data because it's very subjective to the person who is viewing that experiment so what i deem as being dark pink someone else might deem as being medium pink color it's subjective however what we need to do to be more accurate is have quantitative data and here what they've done is used a biosensor this biosensor they've used in this particular investigation has recorded the absorbance of this particular um pigment that's been released now that this is a colorometer this is a biosensor linked into a chlorometer however the more basic chlorometers that you're probably used to using within your a level biology lab are more like this and these are the ones we need to get um used to describing an air exam in our exams so when we're using our colorometer here to look at the different color changes within my um pigment that's been released from my beetroot what we need to do here before i fill a cuvette with my solution from my experiment i have to use a cuvette that's got just water in it it's known as a blank and what i do is i put the blank into my chlorometer i close a lid and i press this value here this number here that says calibrate and this will calibrate to zero my absorbance is zero which tells my color emitter that my absorbance of light should be nothing because that's comparing it to the water sample that blank water i need to make sure that my filter is a red filter at the moment that is set to blue i need to make sure it's red and i also need to make sure i've got absorbance here so once i've calibrated to a blank of water i take out my blank of water i put in a cuvette that's got my first solution of colored pigment solution from a certain temperature and i record the absorbance i take that out i then put my blank back in and i calibrate it and we do we calibrate in between each sample that i'm going to be looking at once you've done that you'll end up with a list of absorptions taken at different temperatures so as we can see here as the temperature increases i will get an increase in my absorbance because i've got more pigment that has been released from my samples of beetroot and the reasoning behind this is because the membrane has become damaged due to that increase in kinetic energy and that conclusion is up there for you to look at