so in the previous video we talked about the light dependent reaction where we looked at the two processes that happens during the light dependent to reaction which are noncyclic photo phosphorilation to produce ATP and reduced NP and also cyclic photo phosphorilation where only ATP is produced but no matter what these products will need to be used in the light independent reaction so if you remember light independent to reaction is where two very important things need to happen where with the help of carbon dioxide ATP and reduced NP there must be the formation of carbon carbon bonds and carbon hydrogen bonds to form the organic molecules another very important thing to know about the light independent reaction is it can also be referred to as something called the Kelvin cycle so if you see the word Kelvin cycle in the exam just know that they mean the light independent reaction those two terms are used interchangeably so don't worry about that now what is very important to know about light independent reaction or the Kelvin cycle is that this process happens in the stroma of the chloroplast just showing you a diagram of the chloroplast here the stroma is the space that I've highlighted in blue and the purpose of the light independent reaction is for the formation of organic molecules for example sample glucose but uh Kelvin cycle can also form other things such as fructose amino acids even phospholipids and fatty acids as well and we will see how this process how this happens what I need you to understand about light independent reaction here before we begin is as follows you don't have to memorize this part so you can skip this part if you want to now I'm showing you three carbon dioxide molecules here and remember light independent reaction carbon carbon bonds have to be formed because we want to make the organic molecule but here's the thing it is impossible for the plants to directly join the carbon dioxide molecules together the reason why is because carbon dioxide is extremely stable and if you wanted to join carbon dioxide to another carbon dioxide to another carbon dioxide the amount of energy needed by the plant is insurmountable it is just impossible to reach that level of energy so what plants do is plants decide to take a slightly more complicated approach to form the carbon carbon bonds okay I going to show you a very detailed explanation of the light independent reaction I don't need you to memorize this part of the video but it helps us understand the Kelvin cycle or the light independent reaction in detail so I would recommend that you watch this part of the video as well now I know we want to make glucose molecules and glucose is made up of six carbon but for the sake of Simplicity let's just start with three carbon dioxide molecules which are represented in those black dots so each dot represents one carbon dioxide molecule now in this troma of the chloroplast there will be another molecule called r ubp ribulose bisphosphate in the exam you can just call it rubp that's okay and if you look at the rubp they are a five carbon molecule represented by those five orange circles joined with each other so one molecule of rubp is made up of five carbon all right what needs to happen first is because the carbon dioxide molecules cannot be joined directly with each other as I've mentioned earlier the plants have evolved where they take one of the carbon dioxide and join it together with one of the rubp and that process is known as the carox of rubp carox just means adding carbon or a carbon dioxide molecule in this case and it is very important that you need to know it uses an enzyme and the name of the enzyme is called rubisco now some students will go that's a very weird name for the enzyme right if we were to explain rubisco's full name the name the full name of rubisco is ribulose bisphosphate carox so it's too long so what scientists have done is they have just basically uh shortened it and they say that the name of the enzyme is called lisco you need to know the name of the enzyme by the way because this enzyme is one of the most common enzymes found in the world because every plant or every photosynthetic organism has this particular enzyme okay now once the rubp and one carbon dioxide molecule have been joined it forms another molecule over there which is how many carbon six carbon as you can see there but remember you still have another two carbon dioxide molecules which have not been involved in the process so what needs to happen is the plant needs to have three rubp molecule so each of the rubp can join to one of the carbon dioxide and therefore they form the six carbon molecule now when they form the six carbon molecule the important thing to understand here is it is unstable okay it is just an intermediate that is very unstable and what will happen is it will spontaneously break down but it doesn't break down in the way you think it does where it just removes the carbon dioxide no it breaks down right in the middle okay splits equally and it becomes this three carbon molecules these are all the three carbon molecules and in this case over here these three carbon molecules are called glycerate phosphate and in the exam you can just mention GP or some books will call it phosphoglycerate or they can just shorten it to become PG yes in the exam you can just put the word GP or PG that's fine right now what's interesting here is technically you have already formed the carbon carbon bonds now you didn't join each of the carbon dioxide with each other yes but but you have formed a three carbon molecule indirectly so that's how plants bypass that earlier problem of the stable carbon dioxide molecules so once the formation of carbon carbon bonds have happened the next thing that needs to happen is the formation of carbon hydrogen bonds okay so where's the hydrogen going to come from because the GP or the PG require hydrogen who is going to give the hydrogen you guessed it it has to come from the reduced nadp so the Second Step that needs to happen is the reduction of GP or PG why reduction because they have to receive the hydrogen and the hydrogen will be provided by reduced NP where the reduced nadp as you can see here they will release the hydrogen and as they release the hydrogen the nadp is then regenerated and the hydrogen is accepted by the GP orpg so to simplify this we just have to say reduce NP becomes NP and for the hydrogen to be attached to those molecules GP or PG they require ATP because ATP provides the energy for the carbon hydrogen bonds to form and after ATP provides the energy becomes ADP and phosphate and the GP is now converted into something called trios phosphates so comparing GP and trios phosph pH Fates or TP trios phosphates have the carbon carbon bonds and the carbon hydrogen bonds as well now here's the interesting thing what exactly is trios by the way when you see the word TR it is three carbon o is just basically sugar so guess what you've already made some organic molecules yes it's not glucose but who cares we've made some organic molecules and the organic molecule in this case is a three carbon sugar now here's where it becomes very important I want you to see in a cycle whatever you begin with you must get it back again what I mean by that is you begin the cycle with three rubp molecules okay the most important thing in a cycle is if you begin with three rubp you need to get those three rubp molecules back okay now I want you to look at those three rubp molecules and I want you to count how many carbon are there in total you can see a total of 15 carbon where five carbon in each rubp multiped by 3 equal 15 carbon now look at the trios phosphates I have six trios phosphates over here my question to you here is as follows how many trios phosphates are required to regenerate three rubp in this case I only need five of the thos phosphate molecules why five of the trios phosphate molecules because if I just basically Encompass the five trios phosphates how many carbon are there in total 3 6 9 12 15 so I can use those five trios phosphate molecules to regenerate the rubp okay where the trios phosphate will be broken down reformed broken down reformed broken down reformed and I'll regenerate my three rubp molecules but this process requires ATP that's why in the light dependent reaction when we talked about light dependent reaction earlier extra ATP needs to be produced so that the Regeneration of rubp can happen now you only used five of the trios phosphates to regenerate the rubp you are still left with one phos phosphate what do we do with that well that is the organic molecule and that organic molecule will be used to make your glucose amino acids or whatever so the steps in light independent reaction or kelvin cycle are split are divided into three where the first thing is carbox of rubp using the enzyme rubisco second reduction of GP or PG and third the Regeneration of rubp to simplify this for the exam okay this is what you just need to know for the exam rubp which is a five carbon molecule is carboxilate with well carbon dioxide catalyzed by the enzyme rubis scope it forms a six carbon unstable molecule which splits to become PG or GP PG or GP under go reduction but for the reduction to happen where they receive the hydrogen to form the carbon hydrogen bonds that process requires ATP and also reduced NP then you get something called trios phosphate or TP you can just put the word TP in the exam don't worry about that and some of the TP have to be regenerated back into rubp and that process requires ATP in my in my video here I didn't write the fact that it requires ATP so could you please add that as well all right now but not all the trios phosphates will be used to regenerate the rubp the excess trios phosphates that you get will be used to synthesize organic molecules such as hexo sugars examples of hexos sugars six carbon sugars will be things like glucose fructose and such so some of the glucose can be converted into cellulose beta glucose converted into plant cellulose which is the part of the plant cell wall some of the hexo sugars can be condensed together to form sucrose where they can be translocated to the sink through the flm some of this glucose can be converted into starch to be used as energy storage one very important thing to also know is some of the organic molecule the trios phosphates can be added together with ammonium or nitrate which contains nitrogen and when they added with ammonium or nitrate they can form amino acids so remember photosynthesis is not just to form glucose it's to form all the other organic molecules as well okay in fact here's the weird thing sometimes the phos you don't have to memorize this but sometimes the phosphoglycerates or the GPS uh pgs or GPS which I've highlighted in pink they can be directly converted into fatty acids and glycerol which can be used to make your phospholipids and tri glycerides so you don't have to memorize the ones where I have uh talk where where I'm talking about fatty acids and glycerol but you do need to know that some of the thos phosphates can be converted into glucose which becomes starch cellulose or sucrose or some of them have to be added together with ammonium or nitrate to become amino acids that part is very important so that's basically what we have to know about the Kelvin cycle or light independent reaction