 Assalamu alaikum. Today we are going to talk about food chains and the food webs. Food chains are actually the flow of energy or flow of food from one level of the biotic factors to another level of the biotic factors. Food chain is we can say a one-way flow of energy in the form of foods. Food webs are the networks of feeding relationships. The relationships between different traffic levels and the relationships between within different traffic levels. A network of eating and being eaten is present inside an ecosystem. So, we are going to talk about the food chains and food webs. But before going to the food chains and food webs, we have to look at the ecosystem and its biotic components briefly. Then we will talk about the food chains and food webs. Ecosystem is an area in which the biotic factors, the living organisms are present in interaction with each other. And in interaction with their surroundings, with their non-living surroundings. We call it an ecosystem. Biotic factors, the living organisms which are interacting with each other and which are also interacting with their physical and chemical surroundings. Ecosystems, there are of many kinds of ecosystems. We widely divide them into two major categories. The aquatic ecosystems and the terrestrial ecosystems. Aquatic ecosystems. Ecosystems present inside the water. Terrestrial ecosystems. Ecosystems present on land. So, ecosystems could be present in water. That is organisms living in water interact with each other and they interact with the water and they interact with their physical surroundings. Organisms living in terrestrial ecosystems of different kinds and they are also interacting with each other. And they are also interacting with their physical surroundings and their chemical surroundings. We call them ecosystem. Ecosystems have biotic factors. We are talking about only biotic factors. The ecosystem consists of biotic factors and the abiotic factors. Biotic factors, the living factors. The living parts of the ecosystem. The plants, animals, bacteria, fungi, viruses. All of the living components of the ecosystem. The abiotic factors though are equally important because biotic factors, the living organisms depend upon the physical factors. The abiotic factors like sunlight. As we know that sunlight is the only source of energy in the ecosystem. And all of the energy which is circulating inside the biosphere is coming through sunlight. Water. Water is also an abiotic factor but we know that this is extremely important for the living life forms. Because no life can exist without water. Rain is a very important physical factor. Soil is a very important physical factor because soil supports living organisms. The trees, the plants, they grow and exist in the soil. So abiotic factors are equally important than that of biotic factors. But because we are concerned here with food chains and food webs. So we will concentrate more on biotic factors. The biotic factors consist of living organisms. We categorize them according to their feeding levels or the trophic levels into producers, consumers and the decomposers. Producers, the plants, algae, photosynthetic bacteria, phytoplankton, all of the living organisms that have the capability of utilizing sunlight as energy source and converting that sunlight energy into the chemical form of energy called the adenosine triphosphate ATP. And also through a process called photosynthesis and also through another process called galvancyl to produce carbohydrates which are the first organic carbon molecules inside an ecosystem. Because all of the other life forms, the animals and the other organisms they depend upon that organic carbon. Then comes the consumers, the second part of biotic factors which eat upon and they get there or acquire their energy mainly or primarily from eating plants. They are called consumers because they can consume plants initially or then other animals consume animals or we say eat animals but those animals which are being eaten are actually eating the plants. So ultimately they have to consume animals and then plants. Consumers consist mainly of animals, consumers have their own types the herbivores, the carnivores and the omnivores, then the decomposers. Decomposers also have extremely important role because these are the organisms who have to break down the dead organic matters that is the decompose the dead organic matter and convert it into very small molecules and compounds and these compounds are taken up or we can say eaten up by the plants and plants then use them for their life processes. So energy which was coming through plants come to the consumers come to the decomposers and then go back towards the plants. Biotic factors they are in relationship with each other. Biotic factors are also interaction with the abiotic factors. The feeding relationship between the biotic factors is called a food chain. If there is a straight feeding relationship we call it a food chain. If there is a complex feeding relationship we call it a food web. So there are three major trophic levels. Producers, the plants, the algae, the photosynthetic protista, unicellular organisms, photosynthetic bacteria, the consumers which consist of different types of animals, plant eating animals, the meat eating animals, then the decomposers, the third level which are fungi, different types of bacteria and some different types of worms like earthworm. So trophic level consist of producers, consumers, decomposers. We also briefly talk about pyramids in an ecosystem. When we are looking at trophic levels we always make pyramids. Pyramids are actually conical diagrams which shows the relationship between different feeding levels. The producers always come at the base, they are maximum in numbers, they produce energy and they produce carbohydrates for all other life forms. Then comes the consumers, less than in number than producers because they have to consume the producers. Then the decomposers which have to decompose both the producers and the consumers, the bacteria, the fungi, they are usually more less, in terms of numbers, more less in comparison to producers and the consumers.