welcome to another episode of igc biology revision today we're going to be looking at section six of the syllabus Plant Nutrition and now I've underlined some of the sections in green and um those are the practical components that I'll be covering in another video so I guess it's easiest to start off with the basics what is photosynthesis now photosynthesis is defined as a process by which plants make carb carbohydrates from raw material using energy from light now those that are undertaking The Core Curriculum then you just need to know the word equation for photosynthesis which is carbon dioxide uh plus water and uh with chlorophyll and light making oxygen and glucose now for those that are taking the extended curriculum you just need to know a bit more than that and uh know the chemical uh equations for that so it's uh 6 CO2 uh plus 6 H2O making 6 uh 602 and C6 h12 six which is uh which is glucose now uh the role of chlorophyll is to transfer light energy uh into chemical energy which is present in uh in glucose and uh once that is done glucose is converted into starch for storage inside leaves now I don't know if you've come across this term before but um the concept of limiting factors is a really important one in your core so by definition it's something present in the environment in such a short supply that it restricts life processes now I think this is a bit of a bit of a weird way to put it I think um an easier way would be uh to word it like a process like photosynthesis uh that requires several factors okay so we looked at light carbon dioxide Etc uh the factor in the shortest Supply is the limiting factor okay so if you don't quite get it then um I'll just give you an example here and hopefully that sums it up a bit so let's just say you're making sandwiches okay you're making sandwiches as far f as you can and the ingredients that you're using are bread lettuce and ham so um you're in charge of making the sandwich whereas you've got three friends uh and they're each in charge of one of the three ingredients and they hand you their respective ingredients as you make your sandwich all right so two of your friends uh in charge of the bread and lettuce are really really fast so um whenever whenever it is the bread and lettuce is always ready to go unfortunately uh the friend that is in charge of the ham is not as quick so even though you always have enough bread and lettuce to make the sandwich you can't exactly make the sandwich without receiving the ham so essentially no matter how fast the other two friends are the rate at which you make your sandwiches will be determined by how fast your slowest friend gives you the ham so in this case the ham is the limiting factor so some limiting factors of photosynthesis would be light carbon dioxide and temperature so you might be wondering why water is not a limiting factor even though it's one of the raw materials required for photosynthesis uh there's a good reason for this but uh you don't need to be concerned with this because it's not within the scope of your core so um we're just going to take a look at each of the grph one by one so uh we can see that as you increase the intensity of light the rate of photos rate of photosynthesis starts to increase okay so as it increases up to this point here where it Peaks this is when light is a limiting factor okay so light is the hammer in this case So the faster you give the faster your friend gives you the ham the faster you can make the sandwich as with light the more light you have um the faster the rate of photosynthesis because light is the limiting factor now when it uh kind of reaches a flat surface like this on the graph it means that no matter how much more light you have the rate of photosynthesis is not going to increase now that's when you can say that light is not the limiting factor now and another factor is the limiting factor you don't know what it is you just know that it's not light anymore same with carbon dioxide uh you have an increasing rate of photosynthesis with an increasing amount of uh carbon dioxide until a certain point where carbon dioxide is no longer the limiting factor and something else is uh temperature at really low temperatures uh molecules don't move really that quickly so the rate of photosynthesis is low and um so up to this PE care temperature can also be a limiting factor where um as you increase the temperature it goes more towards the optimal temperature of the enzymes used in photosynthesis and eventually reaches a peak now unlike the other two graphs this graph does not flatten out because the more higher the temperature the more likely you'll end up denaturing the enzymes um if you took a look at my previous video about enzymes so uh you can see that um if if the temperature if the temperature gets too high the rate of photosynthesis will uh decrease entirely back to zero because uh the enzymes will all become denatured and uh the plant will die now um I'm just going to really really quickly uh cover the structure of a leaf um so not only for for core uh for the Core Curriculum you just need to know how to identify the structures in a transverse section of a leaf but for those of you that are taking the extended curriculum then you need to understand uh the adaptations of the leaf and it structure es in order to maximize the efficiency of photosynthesis so just going from top to bottom we've got the waxy cuticle at the top of the leaf you have the upper epidermis made of epidermal cells you've got the pisan misil layer which is made of of pisan misil cells next you've got the spongy mopy layer made of spongy mopy cells and in the lower epidermis you've got um a line of epidermal cells once again but uh you also have something called guard cells which um has a gap in the middle and it it is able to control the size of this Gap and we call this Gap stomata now stomata is really important because for photosynthesis uh gas exchange is always happening so it for photosynthesis you the plants require carbon dioxide whereas it releases oxygen so um this the space is important for it to uh kind of like take in the carbon dioxide and let out the oxygen that it makes from photosynthesis uh the spongy misil there you can see that it is really really loose compared to the palis mopy layer and that is also in order to maximize gas exchange so you need a space uh for the gas to kind of diffuse into and diffuse out of and that's really really good at doing that and um not only that spongy mophy cells Al also actually have chloroplast and chlorophyll in them as well so they can use it to kind of uh photosynthesize directly too and of course the pet mopy layer is a very probably the most important layer when it comes to photosynthesis and I've covered their adaptations in um another video of uh syllabus 2.3 levels of organization so um if you haven't watched that then I suggest that you check it out and finally we have um the mineral requirements that uh plants need in order for survival so you've got nitrate ions which is used to make amino acids and we talked about how how amino acids are um are made to make protein so without protein uh nitrate deficiency will lead to slow growth and uh so the stems become weak and the lower leaves become yellow whereas the upper leaves become pale green now magnesium is made um is is Ed for making chlorophyll so um if you don't have chlorophyll the leaves will turn yellow because uh chlorophyll is what makes the leaf green in the first place so the leaves turn yellow and the plant growth will slow because there's not as much photosynthesis going on so thank you for watching and um I'll see you next episode