 So one of the major mechanisms for the transfer of energy from the Sun to the surface of the planet is photosynthesis. So I'm just going to talk about photosynthesis a little bit more. And photosynthesis is the domain of green plants, typically green plants, and what the story is is that the internal makeup of the cells of plants has a mechanism that allows the plant to transfer energy from the Sun, light energy from the Sun into food, if you like, glucose. So the process whereby it does that can be written as a word equation. So the word equation is that the plant takes in CO2 plus water and in the presence of light energy generates glucose and oxygen. So this is the photosynthesis equation and it's really quite important to us and other organisms in the biosphere because the generation of glucose at this point brings in food, which is a kind of chemical potential energy. So that's what food is. It stores energy in the form of sugars and then at some point something can consume that and use it to generate energy. But while we're talking about plants, I want to talk about something a little bit more specific to do with the cells and plants. And there are three main ways that the cells differ in plants, differ from the cells in animals. So there's a very good reason for this. Now one of the ones, I'm just going to label the nucleus because every cell has a nucleus and there are other cellular organelles in there. But the ones that are of particular interest, and I don't know if you can see this old label in blue as well, are the chloroplasts. Now the chloroplasts contain chlorophyll and chlorophyll is often the green material that imparts the green coloration in leaves. I know there are some variations where leaves can be goldy colors or red colors, but typically they're green. And it's this chlorophyll in the chloroplasts that is the engine house if you like for converting energy from the sun, light energy from the sun into glucose. The other things while we're here that are characteristics of plant cells that animal cells don't have are a large fluid filled vacuole. You can have vacuoles in animal cells but they're not as large as these ones and this is significant for a reason I'm about to explain. And then they also have very rigid cell walls. The point about the fluid filled vacuole and the rigid cell walls is that plants don't have skeletons to hold them upright. And so even though we're busily talking about energy systems, the other things that plants need to do at the cellular level is have a mechanism for holding the plant upright. And so what happens is there's a combination of things here where the rigid cell walls generally hold the cell quite stiffly and then filling the vacuole makes the cell rigid. That is makes it rigid because it's filled with water and our plant stands upright. And you'll know yourself that if you forget to water your plant, i.e. the vacuole is not filled with water, then the whole thing kind of, you know, wilts and doesn't look too good. But if you put water on it, it goes again. So that's a sort of a separate thing but you can't really talk about the nature of plant cells without talking about those things as well. So getting back to this photosynthesis equation. One of the things that's really cool about this is that if you learn this even as a word equation, although we can also do it as a chemical equation and we probably should do that. So one of the things that's important about the photosynthesis equation, and here I've written it as a word equation but we should be able to write it as a chemical equation as well, is that if we reverse it, that is if we follow it back the other way, then what most organisms do is consume this breathe in oxygen, consume food or glucose and when we do that, going back this way, we generate energy for us to, you know, go for a run or do the things that we do and we breathe out CO2 and water vapor. And so the process back the other way is the process of respiration in organisms like you and me. So that's quite a nice balance there. So I kind of like it too because if you learn one equation, you kind of get two concepts for the price of one. So that's one of the main mechanisms for getting energy from the sun to the surface of the Earth and particularly how it influences the biosphere.