 trophic structures, the consumers, first the contents, definition of consumers, then primary consumers, secondary consumers and the tertiary consumers. So first the consumers, students actually consumers are those organisms which are unable to synthesize their food from inorganic compounds. We have such organisms in the ecosystem which cannot synthesize their food from inorganic compounds. The simple meaning of this is that if we leave the plants, leave the green plants, or leave some extreme bacteria, or leave all the other organisms, they are all the consumers. That is what we will get in the cashmere. So consumers actually utilize the living organic matter from the other organisms. What we will do is that the other organisms utilize the organic matter from inorganic compounds. So normally they eat the other organisms. What we will do after eating the other organisms? We will harvest our food or nutrition. So all the animals, they are consumers. All the animals will come to consumers. So we divide consumers in different categories. We divide them on the basis of their method of nutrition. We divide them in different categories. So primary consumers are those consumers which feed on green plants. So primary consumers take their food on green plants. Now we have if some animal is eating grasses, that is primary consumer, if some animal is eating seeds, that is also primary consumer, like birds, primary consumers will come. If some animal is eating fruits, if some animal is eating monkeys or other animals are eating fruits, then what will happen is that it will come to primary consumer. So any product of the plant will be utilized, that is the primary consumers. We call primary consumers as herbivores in general terms. Herbivores means the plants that they utilize. So primary consumers, they make the second trophic level. Producers first trophic level or primary consumer, they are actually the second trophic level. Then secondary consumers. After primary consumers, we will have secondary consumers. So secondary consumers are those consumers which are obtaining their nutrition from the primary consumers. So secondary consumers will take their nutrition from the primary consumers. How will they take it? By eating them. What will they do by eating them? They will take their nutrition from it. So with this, secondary consumers are also called carnivores in general terms. So what do they do? They eat carnivores, they eat herbivores. So with these examples, we have those who are eating primary consumers, like if insects are eating frogs, that is the secondary frog is the secondary consumer. So if a zebra is eating grass, is it a zebra or is it a primary consumer? But if a zebra is eating a lion or a tiger, that is the lion and tiger, they are the secondary consumers. So with this, when a secondary consumer eats a primary consumer, then the energy from a primary consumer will travel from the second trophic level to the third trophic level. Because the secondary consumer, they make the second trophic level. So tertiary consumers, tertiary consumers are those consumers which eat the secondary consumers. Now every secondary consumer does not have food. But if we talk about the lion, then the lion does not eat anything. So now in this case, if we talk about the frog, then the frog, since it ate insects, then the frog is a secondary consumer. Now if the frog eats a snake, then the snake will be the tertiary consumer. So the snake will be the tertiary consumer. So the tertiary consumer is the secondary consumer which eats the secondary consumers. So the secondary consumers will be the tertiary consumers. Another example is that if a jaguar is eating a secondary consumer, for example, if we talk about the primary consumer, if we talk about the herbivore, if we talk about an animal, a zebra or any other animal, when it will pass through the water body, then normally the crocodiles are there. So crocodiles are the ones who hunt big animals and eat them. So this means that the zebra who tried to cross the water body was the primary consumer. The crocodile has eaten it, that is the secondary consumer. So if the crocodile hunts or eats a jaguar, then this means that the jaguar will be the tertiary consumer since it has eaten the secondary consumer. Now interestingly, the trophic levels, now the tertiary consumers will make the fourth trophic level. In this rare case, there can be a quaternary consumer as well. For example, if the frog ate an insect, then the frog was the secondary consumer. If the frog ate a snake, then the snake is the tertiary consumer. If the snake eats a hawk or a bird, then the bird that will be the quaternary consumer will go to a further trophic level. Now some animals in the ecosystem can change their trophic levels. For example, I have given you an example of a jaguar. If a jaguar hunts a small herbivore, a deer or any other animal, then this means that it is the secondary consumer. But if a jaguar hunts a crocodile, then it is the tertiary consumer. So what are the animals that can change their trophic levels? For example, a monkey or a human. When a human eats fruits, then it is the primary consumer. But when a human eats a flesh or another animal, it will be the secondary consumer. So what will animals do on their trophic levels? They can change their trophic levels according to their needs. But there are many animals in the ecosystem that cannot change their trophic levels. For example, plants cannot change their trophic levels. They will always be on the first trophic level. The next thing is the decomposers. We do not mention decomposers anywhere in the food chain and food web. But virtually they are present at all trophic levels. They are present on every trophic level. Because plants have to decay. They will use a decomposer. They will use a decomposer. They will use a secondary consumer. They will use a decomposer. They will use a tertiary consumer. They will use a decomposer. So decomposers take their food from every trophic level. So we say that decomposers are present at all trophic levels.