 Let's look at the types of nutrition. The way we get food based on the way we get food. There are two kinds of organisms. We have the autotropes and the heterotropes. Autotropes are the ones that make their own food, mostly using photosynthesis. So this is mostly your plans and vegetation. Heterotropes on the other hand, they cannot create their own food. They cannot photosynthesize, which means they rely on eating others. They will either eat other autotropes or they will eat other heterotropes. So let's dig deeper into both of these. Let's start with photosynthesis. Well, to photosynthesize, plants require carbon dioxide, which they get from the air. They also need water, which we get from the rain and when we water the plants and all of that. And they also require sunlight. It's crucial. You cannot photosynthesize without sunlight. And another important component is chloroplast. This is why you and I and donkeys cannot photosynthesize because we don't have chloroplast, even though we have access to carbon dioxide, water and sunlight. You need chloroplast. But what does chloroplast do? Well, chloroplast absorbs the sun's energy and then uses it to split water. So when you split water, you get hydrogen and oxygen. So the oxygen is thrown out as O2. This is why we need plants because they give us oxygen. And then within a series of steps, it is able to convert carbon dioxide into sugars, which is the main source of food. So sugars, what's the formula for that? It is C6H12O6. Now this is not a balanced equation. Can you pause the video and see if you can balance it on your own first? All right. I start by looking at carbon six. There are six carbons and there's only one carbon over here. So clearly this needs to go to six. And then I also see there are 12 hydrogens but there are only two. So this goes to six. And now finally I can see there are 12 oxygens. I have only six oxygens over here. This is six over here. So to balance, I have to put in the six over here. But plants need one more thing. How do they absorb carbon dioxide from the air? And how do they throw out oxygen back into the air? Ah, to do that, they have small openings in their leaves. These openings are called stomata. So stomatas are basically tiny openings or tiny pores. But there's a problem with from these openings plants can also lose water. And if plants lose a lot of water, they can easily die. So what we need is a mechanism in which these openings stay open only when there's enough water but they stay closed when there's not much water. So how do you achieve that? Well, you achieve that by having a couple of balloon shaped cells called gar cells on top of these stomata. Now when there's not much water, they are shrunk and they pretty much close the opening. But when they photosynthesize, they also have chloroplasts. So when they photosynthesize, there's a lot of water inside of them. So they puff up and they tend to elongate. But the important thing is they are fixed at the ends. So they don't have space to elongate and therefore they end up bending away when they puff up, exposing that opening, exposing that stomata. And so notice you achieve what we wanted when there's a lot of water, automatically this pore opens when there's not much water, the pore stays closed. Beautiful, isn't it? Now let's talk about heterotropes. You may wonder what's there to talk about them. They just eat others, right? But wait, Yumi and donkeys can eat others as whole food because we can digest food inside. We have a digestive system. So such animals like Yumi, donkeys who can digest food inside, we call them holozoic animals because we eat whole food. And this is most animals that we think of. But what about bacteria and fungi? They don't have a digestive system. They can't digest the food inside. So you know what they do? They digest the food outside and such organisms are called saffrofites, mostly bacteria and fungi. How do they digest the food outside? Well, they spit some chemicals on the food which actually breaks them down and that starts digestion. And that's what causes rotting. All the rotting is basically saffrofites trying to spit chemicals and digesting the food outside. Saffro basically means rotting. But what about organisms that can neither digest the food inside nor outside? What will they do? Well, they are called parasites. They will just steal the nutrients, the digested nutrients from their hosts. For example, leech, suck our blood and just directly steal the nutrients from us. We become the hosts for them. Similarly, tapeworms and lices, they do the same thing. I used to think that parasites try to kill us but no, they want us. They're alive because they want us to digest food so that they can steal from us. And I find it so fascinating that if you just consider the way we get our food, there is so much diversity in nature.