 Let's explore tropic levels and how energy flows within them. So a tropic level is a diagrammatic representation of how we all get our food. At the bottom, we have the producers, which is basically plants and vegetation. They're called so because they produce their own food from sunlight. Then comes your primary consumers, like the deers, rabbits, insects and so on, which are basically herbivores. They get their food from the producers. They eat the producers directly. That's why they're called primary consumers because they eat them directly. Then you have secondary consumers. How do they get their food? Well, they eat the primary consumers. You can think of them as carnivores animals, but usually these are smaller carnivores in the sense that they are not at the top. There are other animals that can eat them as well. And then that finally brings us to the tertiary consumers. Think of them as a large carnivores. They are at the top of the food chain. They are the apex predators. It's like Yumi humans, tigers, eagles and so on. These are also called as tropic levels. So you can think of this as level one, level two, level three, this is level four. In some cases you can have more levels. You can have up to five levels or six levels maybe sometimes, but it usually doesn't exceed that. And we also see that the bottom of the tropic level, the producers, they are usually the maximum in numbers. You have the most number of individuals over here. However, if you, as you go up the tropic level, the number of individuals reduces. And that's why we have a pyramid over here. So you have the minimum number of apex predators, tertiary, the top of the food chain, minimum number of tertiary consumers. But why is that? To answer this question, we need to look at how the energy flows. Now before I talk about the energy flow, let me talk a little bit about the food chain and the food web. So in reality, things are not so straightforward. We have something called as the food web. It's called so because it actually, if you try to map out who it's whom, you will see it's actually a web, mainly because, you know, animals can eat multiple things. Like for example, snakes can eat frogs, they can eat tiny birds. The reason why things get a little bit more complex. But you still see the levels. You see the tropical level one. You have the producers. You have the primary consumers, the herbivores. You have the secondary consumers, the small carnivores. And then you have these apex predators. You have the large carnivores. You have the tertiary consumers. The second complication is that there is another class of organisms called the decomposers. Let me just shift this a little bit up. Okay. The decomposers, we don't put them over here because these are the ones that eat dead things, all of them. They eat all of them once they're dead. These can be your mushrooms, your bacteria. So they're also a part of our ecosystem, but they don't fit anywhere in the topic levels. And finally, some animals are both herbivores and carnivores. We call them omnivorous animals. For example, human beings. We eat both vegetables and meat. So doesn't that mean that we should also be a primary consumer? So human beings should also come over here, right? But of course, nobody eats us and therefore it doesn't make sense to bring us over here. All this is to tell you that this is not so straightforward. There will always be exceptions. Yes, we are sort of doing classification because we need to classify to make sense of everything, but it's not so straightforward. Things will, there will always be exceptions. A lot of things will not fit. So remember that for the rest of the video. Anyways, coming back to our main question. Why do we see most individuals here and less over here? And why do we see only four to five levels and not more than that? So it has all got to do with energy. Let's think about energy. See, the reason we eat food is because we want energy. So where do producers get their energy from? Well, they get their energy from the sun. So the producers get energy from the sun. Photosynthesis, and that's how they store their energy. What about primary consumers? Well, they get the energy when they eat the producers, right? But here's the thing. They don't get all the energy over here. In fact, studies have shown that they get only about 10% of the energy. When they eat only about 10% of the energy they're able to store, where does the rest of it go? Well, the rest of it is wasted. It goes as a heat into the environment. And that heat is generated at multiple levels. For example, when you are digesting food, you get heat. When you are doing respiration, you get heat. And so a lot of energy gets wasted. And guess what? The same thing happens when secondary consumers eat them. It turns out now only 10% of their energy gets transferred. So that means even less energy gets transferred. Only 10% of their energy goes. And similarly, when third-gen consumers eat them, only 10% of their energy goes over there. So you can see the amount of energy keeps reducing as we go up the tropic level. And after a point, we'll just not have enough energy to sustain life. And that's the reason why we only have about four to five levels, max, not more than that. And this also explains why you have less number of individuals over here. Because if you have the least amount of energy coming in over here, then it's very hard to get that food. You need to eat a lot of food. And so naturally, it's hard to evolve to apex predators. And that's why we have the minimum number of these individuals. Well, over here, they get directly energy from the sun. It's very easy to get that energy. And therefore, you have the maximum number of producers. But there's one more thing to consider when we think about tropic levels. And that is called biological magnification. This is where as we go at top of the food chain, top of the tropic levels, the harmful substances like pesticides and stuff, their concentration increases. Let's see how. So we directly spray pesticides over here. So that's how they get them, how that's how the producers get them. And then these primary consumers eat them and that's how the pesticides goes inside them. But guess what? Remember, these can also eat other producers, right? And so they might get more pesticides from them as well. And therefore, the amount of pesticides actually starts increasing. And now as the secondary consumers eat them, they will have even more pesticides. Because again, remember, they eat multiple things. And so you get even more pesticides. Let me just use black to show that now. Even more pesticides. Then finally, as the apex producers eat them, they will have even more pesticides. And so can you see that the amount of pesticides, the concentration of the pesticides has now increased in our bodies. And so that concentration has become magnified. And this is why we call it, we call biological magnification. So the amount of harmful stuff that goes into our body, that's not good for life, that also keeps increasing. And also another reason why we don't have a lot of traffic levels, also the reason why we have a lot less of these individuals.