 So in the prior video we were talking about the structure of bacteria and archaeal cells versus eukaryotic cells. So I want to talk here about photosynthesis in cells. There are a couple types of photosynthesis. The one that's most common produces oxygen from water. There are also ones that produce that sulfite, sulfate from sulfide and oxidize iron 3 plus from iron 2 plus and can oxidize organics. But what I'm going to talk about here is what we normally think of photosynthesis that actually produces oxygen. And this does not happen in archaea. It happens in bacteria and in particular cyanobacteria are the ones that invented oxygen producing photosynthesis. So the structure of cyanobacterial cells is very similar to that of other bacteria. But in addition they have these extra membranes called thalacoids that hold the photosynthesis apparatus. So the photosynthesis occurs in these extra membranes and the cyanobacteria still have all the DNA and the ribosomes and all of those other components. So the photosynthesis of course allows the organism to take carbon dioxide, water and light to make energy and oxygen. And that energy goes to make organics. So the process where this conversion of the CO2 and energy and light occurs in a different place from the membrane. It occurs in the carboxosome. So it's in the carboxosome that this reaction takes place. And so what happens is the energetic molecules are created. The ATP are created in the thalacoid membrane and those make their way to the carboxosomes which is where the organics are actually created. If we look at eukaryotic cells, so these ones that are photosynthetic are of course plants and algae. In all cases they're doing their photosynthesis in these capsules that are called chloroplasts. And these chloroplasts have a membrane around them and then they have the thalacoid membrane inside and they have a little bit of DNA in them as well. And much like we see for the binocondria that have DNA, this DNA when we actually look at it and compare it, it's really closely related to the cyanobacteria. So the similarity of the process and the enzymes plus the characteristics of the DNA demonstrate that these chloroplasts are the descendants from cyanobacteria. And so this, like the mitochondria, is another case of endosymbiosis with the host cell providing a consistent environment for the ancestor of the chloroplast and the ancestor of the chloroplasts providing energy to that ancestral host cell. So again it's a mutualistic process that allowed plants and algae, the ancestors of plants and algae to become autotrophic to actually not have to eat but to basically be able to take the carbon dioxide from the environment and convert it into a combination of energy and organic matter. And so one of the interesting things about photosynthesis is that it's such a valuable process that has been co-opted by the ancestors of plants and algae. Similarly with the mitochondria, they're so useful that they have been co-opted and integrated into eukaryotic cells. So one of the things that's really special about eukaryotes is the fact that there are these merger of organisms of different ancestry. We have the ancient eukaryotic ancestor that then adopted a bacterium that reacted organic matter with oxygen and some of the ancestral eukaryotes also adopted cyanobacteria to be able to perform photosynthesis. Thanks for watching.