hello and welcome to learn a level biology for free with mr. ik today we're going to be going through the biochemical tests that you need to know for the biological molecules units in a level biology you will probably find it helpful to have some paper nearby so you can make a note of the tests positive results and there's one question slotted in this time as well and for which I'll give you our minds just to pause the video at that point so the biochemical tests that you need to know are and test a link to looking for the presence of three different types of carbohydrates proteins and lipids and the carbohydrates there's only one of the polysaccharides you need to know the test for and those four starch the reducing sugars test you would have learnt at GCSE but we go into the details of why it's called reducing sugar this time and also a non reducing sugars test which will be new so the test for starch first of all the reagent that you have to add is iodine and in this case I've got my sample of starch then you would add your iodine which is a brownie orange color if you have starch present you get a blue-black color so the reagent is iodine positive result is orange to blue black color formed test for reducing sugar so this is the one you would have learnt at GCSE so in this example I'm going to be testing glucose which is a reducing sugar but also show you and the result with just distilled water so you can see what a negative result looks like so I've added Benedict's which is the bright blue reagent to both samples and you have to heat for this reaction to work so the glucose test cheap you can see it's starting to change color water remains blue and that's what our results would be so for a positive result you go from blue to orange for example glucose negative result it remains blue and I used water as an example and you can get other colors other than that bright orange a brick orange red car arrived there and the different colors would indicate the concentration of producing sugar you have so if you only had a green color or green yellow that indicates a low concentration of reducing sugar the more orange red it is the higher the concentration of producing sugar now you might have noticed in the beaker as the reaction was occurring that the color changed at the top of my solution first and I've taken a shot from the video here where we can see that bright orange kind of starting to form at the top first and it's yellowy green and almost still blue down here at the bottom of the test tube so this is the point where just to pause to have a think why is it that the reaction is occurring first at the top of my solution so this links to physics actually and it's to do with the idea of convection currents so the hotter particles in the solution are going to be rising and therefore the hottest point in the solution and the test tubes at the top so the molecules will have the most kinetic energy at this point in the test tube therefore more successful collision collisions and the reaction will be happening faster and therefore kind of change is happening first at the top so next the non reducing sugar test the only non reducing sugar that you learn about is sucrose so I'm going to test a sample of sucrase first thing you have to do though is confirm it isn't a reducing sugar so I'm gonna do the Benedict's test first which we can see leaving it in the hot water with the Benedict's for a few minutes and we've got a negative result so I'm adding sucrose again to now go on to the next step and this is acid hydrolysis so I've added acid to my sample of seed Krays and this time you do have to get it to boiling so I've got my thermometer in the test tube to make sure the acid does get up to 100 degrees C so it's boiling and it has to be boiling for about 2 minutes for acid hydrolysis to happen and what we mean by that is we're going to hydrolyze the glycosidic bonds so the sucrose is going to be converted into glucose and fructose so that's our next stage in the video we have the boiling acid for two minutes I am then going to move it into a beaker of cold water to cool it down for safety reasons and once it's cool add an alkaline then we can add Benedict's and heat again and we'll get a color change and you'll start to see again at the top it's going a red color until eventually the whole solution now got this brick red precipitate so the brick red solid is formed at bottom so that's a positive result when we did retest with Benedict's in heat the Benedict's will from blue to this really dark brick red color to confirm we do have a reducing sugar so just to summarize them what we mean by the reducing versus non reducing sugars the reducing sugars are all of the monosaccharides that you learn so glucose fructose and galactose and two of the disaccharides lactose and maltose so the only non reducing sugar that you learn about is sea kraits and the reason we call them reducing versus non reducing is these five sugars are able to reduce copper sulfate which is blue chemical in Benedict's reagents and they reduce it to copper oxide and copper oxide is a rusty brick red color so that's why it does convert from that blue to the brick red color secrets which is our non reducing sugar isn't able to reduce copper sulfate and that's because the group within these sugars that does the reducing is actually used up in the glycosidic bond in secret so it's not going to reduce copper sulfate to copper oxide hence the name it's a non reducing sugar the reason it does change color though eventually as we hydrolyze seek raise so we boiled it in acid and in doing that that breaks the glycosidic bond between the monomers glucose and fructose so we now end up with those two separate monomers and when we then do the Benedict's test again we do get that brick red color and often you'll find is a very very dark brick red color like we had because you now have two monomers in there glucose and fructose whereas when we were just testing for glucose in the previous experiment we just had one sugar so we had more sugars present that's why it was that brick red color so next test is for preachings and you would add Boyett's which is another bright blue solution i was m Fionn emphasized the pronunciation here so by you ret because often students call it burette which is incorrect that is a piece of equipment that you use in chemistry so by rect is the name of this reagent and I've got albumin as the protein that I'm going to be using so I'm adding my sampler protein and in the bright blue barrette and a positive result is it turns a purpley lilac color so the last test is the test for lipids and I'm going to use oil as my lipids and step one is you have to dissolve the lipid in ethanol so to dissolve it bum on top shake it up and it is dissolved the next stage is you add distilled water and shake again positive result is it's white in color and it's an emotion so you would have to state both of those parts the color and the fact it's an emulsion there's no precipitate there's no solid that has been made it is just an emotion so in summary then the test for monosaccharides and the disaccharides with the exception of secrets is the Benedict's test the test for secrets which is our non reducing sugar would be after a- Benedict's test you would then go on to do acid hydrolysis which is boiling an acid neutralize an alkaline and then heat with Benedict's again and observe the color change the test for starch is iodine test lipids as the emulsion and protein - Bayete test now that is just a brief summary in an exam you would always have to state which chemical you're adding which is the reagent the conditions so that could be whether you have to heat it when if to boil it do you have to mix to dissolve and lastly the kind of change to indicate the presence so state the starting color and the positive color the result and that's what we're going to finish on just summarizing all of the positive test results so lipids was the white emotion proteins is this purpley lilac color starch you get blue black and reducing sugars you can get any color from the green yellow orange brick red the more dark red it is the higher the concentration of reducing sugar so we've got a dark orange in this case so that's it for the biochemical tests you need to know the method and the positive test result so that's it for our lesson today with learn a level biology for free with mrs. trick you can click on the link to go back to any of the biological molecules which were mentioned in this test just to learn the theory on them if you wish