 So in this video I want to talk about primary productivity. All organisms on earth are composed of organic compounds, organic molecules, and the primary productivity is the biological process of going from abiotic carbon, for example carbon dioxide, to organic molecules to make up the bodies. So I'll draw on an example, organic molecule of acetic acid, and this process of going from inorganic carbon to organic molecules requires adding hydrogen atoms and electrons. If we look at the oxidation state of carbon in CO2, it's plus 4, whereas in organic molecules it averages about zero, sometimes a little bit more negative depending on the organic molecule. So the basic process is to go from CO2 and then add protons and add electrons to produce organic matter. So we will just do a simple one here, which is half of an acetic acid. So I'll actually, I can put down this acetic acid, I can make this a 2, this a 2, and then this would need to be 4 hydrogens. So if we're going to balance this out, we have another oxygen on the side, because we have 2 on the side and only 1 so far. And so we can make water as the easiest option here. So this would require 4 protons and 4 electrons to make it charge balance. So the basic process for an organism to convert carbon into a useful organic molecule from carbon dioxide is to add protons and electrons. So the organism has to get those protons or electrons in some way. And the most common way that on earth for these to be produced is through photosynthesis. So we have oxygenic photosynthesis. Photosynthesis produces oxygen and that's the one we're familiar with. It takes water plus light and it converts that into 4 protons plus 4 electrons, 2 waters to do this, plus molecular oxygen. So it takes 2 waters to get the molecular oxygen. These protons and electrons are supplied to the reduction of the carbon in CO2 to produce the organic molecules. The other types of photosynthesis, for example, photosynthesis can oxidize sulfide and in this particular case sulfide plus light goes to elemental sulfur plus 2 protons plus 2 electrons. So that's half as many in that process. There are also chemical reactions that can provide protons and electrons and if it doesn't involve light, we call it chemo synthesis, chemical synthesis, and chemical synthesis can work, for example, with hydrogen and through various processes this can break down into 2 protons plus 2 electrons, again producing those protons and electrons to reduce the carbon in the same way. So the key point is that life needs to have these protons and electrons to create the organic molecules which are the building blocks for life. Thanks for watching.