hi everyone and welcome to miss estri biology and in this video I'm going through the a-level biology explanation of digestion and the absorption this is for AQA Al biology but it applies to most exam boards and one of the key things with this topic is that you need to be really particular with the keywords that you're using to make sure that you get those marks and I emphasize this throughout the video so you can make notes on just that but if you want that all done for you then don't forget that you can get hold of my AAL notes and my flash cards which cover all the key terms and key marking points using the link below straight to my website but for now I'll leave you to this lesson so just to go through the definition of digestion first of all it's where you have large insoluble molecules hydrolized into smaller soluble molecules which can then be absorbed across cell membranes and then into the bloodstream so we're going to go through digestion of carbohydrates lipids and proteins which are the three that you need to know for AQA biology in a level so the two enzymes that you need to know about are amasis and these are um all different types of amasis enzymes and membrane bound disaccharidases and you'll notice that pretty much all enzymes end in as e so if you do ever see a name end in in as e in biology it means it's an enzyme so amalay is produced in the pancreas which we can see um just a tiny bit of here in yellow that's the pancreas but it's also produced in the salivary glands which are up here and for that reason when they're produced in the salivary glands it's secreted into the mouth so that is where digestion of carbohydrates begins in the mouth and then once those um amales have started to hydr the carbohydrate polysac so for example starch into the disaccharides such as molos by hydroling glycosidic bonds that is then swallowed it goes into the stomach and then into the small intestines but it's this very first bit of the small intestine the duodenum which is where the next stage of digestion occurs and within the duodenum and the ilium this is where we have the membrane bound disaccharide AES and those then are able to hydr the um disaccharides into monosaccharides and for example you've got two examples of these membrane bound disaccharidases meaning it's an enzyme that can hydr a disaccharide and you can get sucr which can hydr sucrose into fructose and glucose and lactose which can hydroly lactose into galactose and glucose glucose and that will be occurring in the duodenum and then into the ilium as well proteins then there are three key sets of enzymes that can hydrolize the polymer which is proteins you can have Endo peptidases Endo meaning inside so endopeptidases are enzymes which can hydrolize the peptide bonds between amino acids that are within the center of the polymer chain you also get exop peptidases exom meaning on the outside so these are the enzymes which can hydrolize the peptide bond between the amino acids right at the end of the polymer chain now you'll also get to the point where you probably only have two amino acids still joined together and that's what membrane bound dipeptidases are hydroling and they can hydrolize the peptide bond between just two amino acids or a DI peptide just to point out where this is occurring then so the protein digestion starts in the stomach which is just here then all of that churned up and partially digested um protein material moves down into the duodenum or duodenum and into the ilium and that's where the remaining digestion of proteins occurs lastly then the digestion of lipids and this is slightly different because it does involve enzymes for chemical digestion but it also involves some physical breakdown as well using bio salts and we'll go on to that in a bit more detail in the next slide so the enzyme lipase or lipase is produced in the pancreas and that will then secrete that enzyme into the duodenum and into the ilum and LIPA is able to hydr the Ester bond in triglycerides and that's the bond which holds the glycerol and the Three fatty acids together so when it hydes those three Ester bonds that occur in triglycerides you end up with fatty acids and glycerol but actually you often get monoglycerides and um fatty acids so the next step then is um just referring into these bio salts now this actually occurs before the Lipa action um and bios salts are produced in the liver which is this large organ here gets stored in the galbladder and then through the bod duct it's delivered into the small intestines so the jenim first and those bile salts can emulsify the lipids meaning it splits large droplets into many many many tiny droplets and eventually those will then go towards making m cells so we're going to go through the lipids in more detail there is quite a bit more to say about them so I pointed out you have physical and chemical digestion physical is looking at the emulsification and Mel formation chemical is the action of the enzyme So Physical the lipids get coated in the bile salts um which are being released from the ghoul bladder where it was made in the liver those bile salts coat the lipids and it causes them to split up into tiny droplets and that's what we call an Emulsion you need to know why that is an advantage to digestion and AQA are very specific in their Mark scheme so it's the fact that you get many small droplets and that creates a large surface area however the reason that is an advantage is if you've got a larger surface area you'll get a faster hydris action by lipase because if you're providing a large surface area more of the enzymes can attach you get more enzyme substrate complexes and therefore faster action and that's the key idea you do have to point out you get faster action or faster hydrolysis and that's where it links to the chemical digestion the physical digestion provides the large surface area for that lipas to be able to hydroly lipid into monoglycerides and fatty acids so how this links then to the mels because we've gone through um how you end up these fatty acids and monoglycerides but how do we then get this next stage where those form the mels so firstly is what is a Mel so it is a sphere or a vesicle and it's made up of the fatty acids and monoglycerides that are produced from that hydrolysis or digestion but it's also incorporating in the bile salts so as well and these spheres or these mels they are able to deliver the fatty acids and monoglycerides to the epithelial cells in the ilen they'll then release the fatty acids and glycerol which can move into the epithelial cell by diffusion so that's it for the digestion next is how do all of those digested food molecules get absorbed and all of the absorption is happening within the cells lining the ilium which is part of the small intestines and the key thing and this is similar to gcsc you have these Villi which is the folding of that ilium surface and on the Villi they are covered in several micro Villi cells and zooming in we can see these micro cells they have even further foldings to increase the surface area for more rapid absorption but also it's not shown in this diagram but in the middle of these Villi there is a capillary Network and that enables the concentration gradient to be constantly maintained and also you have a very very short diffusion distance so if we go specifically through how each of the molecules are absorbed now monosaccharides which are the products of digestion of the carbohydrate Ates and amino acids which are the products of digestion of the proteins they are both absorbed in the same way and that is by Co transport now I'm going to link up here my full video on Co transport so I'm not going to go through it in this one just in brief here's some key information um so the glucose an example of a monosaccharide and the amino acids are absorbed as we said by Co transport which is a type of active transport now some will be absorbed by facilitated diffusion but you could get to the point where you have more sugar inside of the epithelial cells and inside of the blood compared to the Lumin and therefore you won't be able to absorb that sugar or amino acids and that's why co-transport a type of active transport is also essential the actual process as I said check out the video on that so the lipid absorption follows on from what we've already said so we've already gone through how you get the mels forming and then just to go into the extra detail so those mels are carrying the fatty acids and the monoglycerides and they deliver that to the cells line in the ilium or the epithelial cells and that delivers um the fatty acids and monoglycerides which can then simply diffuse through that plasma membrane and that is because um they have that non-polar nature meaning they are lipid soluble once those have then entered the cell they need to be formed back into triglycerides so they can be used within the body and that is what is happening inside of the GOI apparatus or the GOI body sometimes in the endoplasmic reticulum and that's what this diagram is showing us here we've got the fatty globules um are being processed and quite often when they're processed they are combined with a protein and if that does happen we then call it a kyom micron so when a triglyceride is combined with a protein that's our kyom Micron the kyom Micron is then released inside of a GOI visle which we can see here the GOI vesicle then moves towards the other end of the epithelial cell and it is released by exocytosis mean meaning is then just released from the cell the vle fuses with the membrane and that releases the contents how that then gets absorbed into the rest of the body is through this um lacal or sometimes it's called a lymph vessel and the lipids which have then been formed or Al kyom Micron are absorbed inside the lacal and they'll get transported around in the lymph and that does eventually drain into the the capillary system so those are the key things that you need to know about absorption and [Music] digestion