[Music] the calvin cycle is the second set of reactions in photosynthesis and occurs after the light dependent reactions sometimes the calvin cycle is called the light independent reactions or even the dark reactions because light is not directly needed to make the calvin cycle happen nevertheless two key products from the light reactions are needed to make the calvin cycle work atp and nadph you may recall that both atp and nadph were made during the light reactions at the thylakoids the calvin cycle takes place in the fluids surrounding the thylakoids known as the stroma atp provides the energy and nadph provides the electrons and hydrogens that are needed to reduce carbon dioxide to build sugars in the calvin cycle here's how it works phase one carbon fixation an enzyme called rubisco takes co2 from the air and adds it to a five carbon compound called ruvp this is called carbon fixation this makes a six carbon compound that immediately splits in half to make two molecules of three phosphoglycerate notice that we did carbon fixation for three molecules of co2 you will see why soon phase two reduction in the reduction phase atp from the light reactions provides energy to make an intermediate compound this reactive intermediate can then be reduced or gain electrons and hydrogen the electrons in hydrogen come from nadph and are used to reduce the intermediate compound to make glyceraldehyde 3-phosphate more commonly called g3p or sometimes trios phosphate g3p is the key product of the calvin cycle that can be used to make sugar notice that for every three molecules of co2 brought into the calvin cycle there's a net gain of one g3p three carbons in three carbons out makes sense right phase three regeneration notice in our model that only one g3p is removed from the cycle but five more remain these five g3p molecules get converted back to our starting compound ruvp remember the calvin cycle is a cycle so we need to make our starting compound again to keep the cycle going now i'm going to give you a moment to think if we have five g3p molecules and each one has three carbons how many carbon atoms do we have now that you have the answer how many five carbon rubp molecules can we make using those carbon atoms i'm guessing that you figured it out we can make three rubp molecules to do this energy is required can you guess where that energy comes from if you said atp you are right let's watch now that we've completed the calvin cycle for three carbon atoms let's go through the process again so that we can make glucose remember our overall photosynthesis equation has six carbon dioxides being used to make one glucose molecule with six carbons with this in mind how many g3ps are needed to make one glucose if you said two you are correct now you have seen how the calvin cycle is used to make glucose and how like dependent reactions provide the nadph and atp that were needed to make the calvin cycle work the glucose and other organic compounds made as a result of these processes in photosynthesis are what allow plants and algae to grow and support practically all life including you to become an expert on the calvin cycle by doing it yourself play photosynthesis interactive at bioman biology [Music]