hi there everyone and welcome to learn a level biology for free weird miss Esther ik in this video I'm going to be going through the surface area to volume ratio and the importance of it in biology so to start then it's all to do with exchange surfaces in organisms and this is what explains how many exchange surfaces whether that's for gas exchange or absorption in digestion they have similar adaptations to try and make the transport across those surfaces more efficient so be looking at the maths behind surface area to volume ratio they will have a look at some examples of adaptations so it's all to do with as I said the relationship between the size of the organism because that is what determines the surface area to volume ratio or it could be structures within the organism which are adaptations to increase the surface area and that is to help significantly with either gas exchange or absorption after digestion so the maths first of all the surface area to volume ratio you could be asked to calculate this in GCSE or an a-level so we're gonna start with some uniform shapes with keeps so this one here is one centimeter by one by one so to work out the surface area you need to work out the area of one side of the cube which would be one times one and then there are six sides to the cube so times by six so the surface area is six centimeters squared the volume is timesing the width by the length by the height so 1 times 1 times 1 which is 1 centimeter cubed the final stage then surface area to volume ratio what that means is divide the surface area by the volume and in that case or this case it's 6 so then if we double the size of one of the lengths so in now instead of one centimeter we have two centimeters let me go through the same idea surface area so we need to work out the surface area of one side of the cube so two times two and then there's six faces to the cube so two times two times six gives us 24 the volume times in the width the length and the height which is two by two by two which is eight 24 divided by 8 is three and then same thing again I've done for three centimeters and what we can see from this is a key pattern the larger the objects in this case cube the smaller the surface area to volume ratio and that is of key importance in biology because if we were to substitute these cubes for organisms what that tells us is very very small microscopic organisms have larger surface area to volume ratios so they'll be able to really efficiently diffuse substances across their surface but as an organism gets bigger their surface area to one ratio drops therefore they can't just diffuse gases across their surface they have to have adaptations inside of them on the outside to help increase their surface area and that's the relevance of this maths in biology so one more example of the maths we've got our surface area of a cuboid this type and we need to work out the surface area of all six sides so to the sides our five by three to the sides are two by five and two of the sides are three by two add that all together our surface area is 62 centimeters squared the volume two times three times five and that comes to 30 surface area divided by the volume which is what the ratio is that comes to two point zero seven so that's one skill link to this topic you could be asked to calculate the surface area to volume ratio and this is what they're referring to the biology element then just to recap that smaller organisms say for example an amoeba naturally have a very large surface area compared to their tiny tiny volume so that means they already have a big enough surface to exchange substances without any additional adaptations and also there's a very very short diffusion distance from the outside to the center of the organism so as a result they don't have any additional adaptations and the way that organisms like amoeba get oxygen for respiration is by simple diffusion across their surface in contrast larger organisms so this would count as humans and you'll be learning about fish which I can link up here you'll be learning about insects and plants as well all as larger organisms and here we can see that larger organisms do have smaller surface area to volume ratios and that also means there's a bigger distance from the outside to the very very center of their body they'll also typically have much higher metabolic rates which means the speed of the chemical reactions and therefore there's bigger demands to remove waste but also to get enough oxygen and glucose to cells for respiration and that's because the bigger you are the more cells you have so as a result larger organisms will have adaptations to try and increase the surface area without reducing their volume too much to provide more efficient exchange surfaces for gas exchange or absorption so last thing then is looking at some of these adaptations so villi and microvilli we have folds here and the villi and the villi themselves are covered in these micro villi which also have additional folds now all of those folds significantly increase the surface area without reducing the volume too much so that increases the surface area to volume ratio for more efficient absorption of digestive feed alveoli and bronchioles so the fact that there are millions of alveoli in both lungs and the bronchioles branch as well increases the surface area and if you want to learn more about that I'll link the video on human gas exchange just sit so insects as well have adaptations to increase the surface area to volume ratio for gas exchange and that is all the spiracles along their abdomen and all of the branching trade keels and tracheal system and again here's the linked video to find out more about gas exchange in terrestrial insects gill filaments and lamellae in fish so yet again another example of adaptations and if you want to know more here's the link for extra details on gas exchange in fish plants also so larger plants do you have adaptations as well so the fact that leaves are really broad and thin that is going to increase the surface area to maximize gas exchange also and then another thing just a bear in mind is the fact that capillaries occur as capillary networks or capillary beds means that there's a very very large number of capillaries providing the large surface area for gas exchange at cells or at tissues so there's the adaptations that larger organisms have to overcome their small surface area to volume ratio to provide a larger surface area to volume ratio at exchange surfaces I hope you found that helpful today if you have give it a thumbs up and make sure you click the subscribe symbol to keep updating latest videos [Music]