this is a summary video on photosynthesis it's geared towards the Irish Leaving Cert boundary course it's made to help my class revise so please be aware that it is a very much summarized version of this topic so just a little piece of advice generally if you don't know about NADPH and ATP those two molecules you will find photosynthesis extremely difficult go back and revise them first photosynthesis is the process by which green plants could make their own food using light energy and it's one of the reasons why we refer to plants as being autotrophs their ultra trophic capable of making their own food and it's also the reason why plants are always found at the bottom of the food pyramids in ecology they are the producers so one of the other things you have to know about photosynthesis is that it's a biological process where light energy is converted to chemical energy by the plant there are four factors necessary for photosynthesis carbon dioxide water chlorophyll and light and if any one of these four factors is missing well then photosynthesis simply will not happen this is the equation that you need to know for your exams it describes what's going on in the process of photosynthesis and it helps you understand what's happening carbon dioxide diffuses into the stomata of the leaves water enters the roots by osmosis and goes upwards to the leaves light gets trapped by chlorophyll in the chloroplast of those plant cells and at the end of the process glucose is produced and so too is oxygen the process mostly happens in the leaves of plants and the reason for this is because the leaves are so well adapted for photosynthesis how well firstly the leaves are thin flat lamina being very thin is good because it allows for the rapid diffusion of carbon dioxide into those cells and the rapid diffusion of oxygen out of the leaf and being flat means that it's very good because it increases the surface area for absorbing all of that sunlight so that's just some of the adaptations of the leaf but be aware that there is a separate video and you have to know the internal structure of the leaf very well so I would watch that later on so let's go into the specifics of what happens in photosynthesis and the trick to this is knowing the structure of the chloroplast really well plant cells you know have the structures known as clear applause and this is where photosynthesis takes place inside the chloroplast you see these green dislike structures flat structures and they're called Tyler codes they're usually stacked in two groups or bundles known as a Granum and when you have a few Granum it's referred to as grana so it's inside these thylakoids are these grana that you find the chlorophyll pigment so chlorophyll and all the other pigments are found in the membrane of the thylakoid so you can see here this is one single thylakoid and remember that they're usually arranged in two Granum photosynthesis is taking place in the chloroplast and specifically we're now looking at the membranes of the thylakoids inside the chloroplast where we find these substances known as pigments these are capable of absorbing different wavelengths of light energy the most important is chlorophyll but there is chlorophyll a and chlorophyll B and many other types of pigments too light is made up of a spectrum of seven colors which represent different wavelengths of light energy chlorophyll the various types of chlorophyll are very well suited to absorbing light energy at either end of the spectrum so they absorb most of the colors of white light except for green and yellow which are reflected to ensure that light is harvested in a very efficient way the pigment molecules are arranged into these structures known as photo systems in the thylakoid membranes photo systems are basically the chlorophyll molecules and the other pigments arranged next to proteins and at the center of which is this reaction center which contains special chlorophyll molecules and an electron acceptor that can accept the electrons that are going to be excited when they absorb all of that light energy so there are two photosystems of note there's photosystem ii and photosystem one photosystem one was discovered first and photosystem ii was discovered second they're basically the same except that their arrangement is slightly different in that one can absorb different wavelengths of energy so the first part of photosynthesis is the light dependent stage and there are two pathways there is pathway one and pathway two let's start with pathway one it's known as the cyclic pathway and it's happening in the thylakoid membranes inside those chloroplasts and it involves only photosystem one so light energy gets absorbed by these pigment Jews that are arranged this photosystem one the light energy is passed from pigment molecule to pigment molecule until it reaches a reaction center chlorophyll this results in electrons being energized and are passed to an electron acceptor molecule energized electrons then get passed over an electron transport chain losing a lot of their excess energy and resulting in the formation of ATP eventually those now low energy electrons return back to chlorophyll in photosystem one so now let's go onto pathway 2 which is known as the non cyclic pathway and you can see from the diagram here that it involves two photosystems photosystem 2 and photosystem one so pathway 2 begins in much the same way as pathway 1 except it begins with photosystem 2 where the pigment molecules absorb their light energy it gets passed from molecule to molecule until it reaches the reaction center chlorophyll here energized electrons then are picked up by the electron acceptor molecule and they are eventually passed over an electron transport chain where ATP is generated the electrons continue on to photosystem 1 so you can see what has happened so far in pathway to basically the electrons have been energized they've passed over an electron transport chain generating a bit of ATP in the process and now they've been passed into photosystem 1 so we're halfway true pathway to energized electrons have so far left chlorophyll in photosystem 2 and gone to photosystem 1 so electrons are now needed to replace those lost by the chlorophyll in photosystem 2 so this is when photolysis of water takes place this is using light energy to split water molecules and it's really done to replace those electrons photolysis of water produces three very important products electrons protons and oxygen the electrons go to replace those lost by chlorophyll in photosystem two the protons go into a proton pool and will eventually be transported by NADPH to the dark stage reactions or the Calvin cycle and the oxygen either gets used internally by the plant cell for respiration but most of it gets released to the atmosphere through the stomata so let's recap energized electrons left reaction Center chlorophyll in photosystem 2 they were picked up by an acceptor molecule and passed over an electron transport chain this resulted in the generation of ATP they then made their way into photosystem one which is now going to absorb more light energy and results in electrons being energized the electrons are now going to be passed by that acceptor molecule to a new molecule and ADP and this is where they're trapped so basically then you have this molecule called nicotinamide adenine dinucleotide phosphate and you have to know its full name it's otherwise referred to as nadp+ it's going to combine or trap two electrons and a proton those protons from the proton pool remember and it's going to form NADPH NADPH is a carrier molecule it's going to carry those electrons and that proton to the dark stage of photosynthesis or the Calvin cycle so the products of the non cyclic pathway are ATP and NADPH the oxygen was produced it was produced as a result of photolysis of water so be very specific so with the light stage completed we're now on to the light independent stage it's so called because it does not use light or need light however it does need the products that were formed in the light stage that ATP and NADPH so it's otherwise referred to as the Calvin cycle or the dark stage reactions the calvin cycle or the dark stage reactions they take place in the stroma of the chloroplast you can see here in the diagram this contains many enzymes and so all the factors that affect enzyme controlled reactions such as temperature and pH they can impact the reactions of the calvin cycle also bear in mind that the reactions of the light stage that the light dependent reactions these happen too quickly are too fast and so are not enzyme controlled so let's get back to the Calvin cycle carbon dioxide which has diffused into the stomata of the leaves is basically going to combine with those electrons and those protons that will be transferred to the stroma by the molecule NADPH once it transfers those electrons and the proton it reverts back to being nadp+ and it goes back to the light dependent stage to do more work so in the calvin cycle then carbon dioxide combines with the electrons and the protons to give glucose that carbohydrate and the reactions are all fueled by the breakdown of ATP which was formed in the light-dependent stage and you know that when ATP breaks down it gives rise to adp and a phosphate and that goes back to the light-dependent stage to generate some more ATP so this diagram is excellent for helping you review just what's gone on in photosynthesis so you know that the whole process takes place in these organelles known as chloroplasts found in plant cells it involves two types of reactions light dependent reactions and light independent reactions so the light stage or the light dependent reactions happens in the Granum or the grana the stacks of thylakoids and it involves the photo lysis of water so that's very unique to the light stage important products such as ATP and NADPH are formed as a result of the light stage reactions are the light dependent reactions and because of photolysis of water oxygen is also formed then the second stage of photosynthesis is known as the calvin cycle sometimes referred to as the dark stage reactions it happens in the stroma of the chloroplast so the liquid part of the chloroplast and it involves the two products made in the light dependent stage ATP and NADPH so NADPH is going to bring electrons and protons which will then combine with the carbon-dioxide to produce glucose and all of their reactions are fueled by the breakdown of ATP that was photosynthesis I hope the video has helped in some way with this topic because I know it's tricky so the very best of look make sure you go on and do pass papers now and you go and use your textbook please be aware that I do include a lot of detail about photosystems they're not on your course I just include them so that if you want to go and look at other videos such as kadek atom II which is amazing and you'll be able to understand them better if you know about photosystems so best of luck and please be aware that these videos are not intended for commercial use and they're not made for monetary gain good luck