[Music] we'll have a look at the first stage of photosynthesis which is the Z scheme or the light dependent stage now as the name implies it is the light dependent stage so it needs light basically and it happens in the follicle membrane as we mentioned in our previous video and I also said that in the follicle membrane there are structures called the photosystems and they are the structures that absorb the lights energy from the Sun from the lamps to do reactions so first of all actually we'll start off with the photosystem 2 now what happens first of all is that water is absorbed from the roots and it travels up to the leaf and then it goes into the follicle membrane and the water is first of all at the photosystem 2 let's say light from the Sun hits photosystem 2 and that light energy is first of all used to brick this water molecule down a half of a BOTY molecule has been released and the other bit will be the hydrogen vents and then finally we also got our electrons being released and these electrons go into the photo son too and they get excited because of the light energy and that's the first step we'll come back to the protons later on we call this entire process photolysis because it's using light photo lysis which is breaking down now these two electrons are actually transferred into structures called that cron carriers so these are electrons once they got released they get carried by the electron carriers and it gets excited and what happens is that the electron carriers will take these electrons with them and go through an electron transport chain for more information on that specific bit I would recommend that you go to see that particular video in the respiration a list but what happens is these electrons eventually lose their energy and they go along the electron carrier and they arrive at photosystem 1 and in the process they will make ATP so they release energy at this point which a system one also absorbs energy from the Sun so they get the light energy and again the electrons gets excited as well at this stage the electrons have a choice they can either go back down to photosystem 1 to release more energy or they can continue on with the cycle and if this stage it really depends on what the core process actually needs over the plants needs so if the fun is lacking energy then they will go into this process which is what we call the cyclic photophosphorylation so they go for the same process as before to go through the electron transport chain again so this is cyclic photophosphorylation because it's a cycle or the electrons will then travel somewhere else so they then arrive at a particular enzyme called an ADP reductase the NADP will receive the two electrons from the scheme here and also a receives two protons that was previously released and these two things combined together will reduce nad p to become reduced any DV be very careful not to be confused with any D which is the coenzyme involved in respiration there are two different things even though they have very similar names now in the process of the protons going to the NAD P reductase they were also passed by another enzyme which is ATP synthase and actually it's the same scenario for these that here it's basically the electron transport chain so imagine that there are also protons being pumped across the membrane in these areas as well as they go through the ATP synthase energy is being released in the form of ATP so if the electrons go in this cycle we call this pot the noncyclic photophosphorylation the reason why we call it phosphorylation is because of the production of ATP in this case where ADP is being phosphorylated make ATP or energy but rather than this is cyclic which is you know as you can see it's repeated whereas this but it goes somewhere else so is a non cyclic and there you have it this is the process of Lisette scheme on the light dependent stage three tap so what water arrives at photosystem two where it absorbs the sunlight to do photolysis meaning using light to break down water in this case it releases an oxygen active and then two protons for truffles elsewhere and also two electrons which gets into the photo two gets taken up by the electron carriers and it gets excited as well as they travel through the electron transport chain they lose the energy by pumping protons across to make ATP 2 and then finally they arrived at photosystem 1 in this case lights gets absorbed again the electrons get excited again they can either go into cyclic photophosphorylation so meaning go back into a net transfer for change to make more ATP or they go into noncyclic photophosphorylation where they meet up with the protons that were previously released at NADP reductase to reduce any DP in the process same thing here this is the electron transport chain same as that but as you can see from this stage we can get a ATP and reduced nad p as the true products and these two will then go on to the Calvin cycle which is the next stage to actually make glucose and we'll have a look at that and see how they do that in the next video