 Assalamu alaikum. Today we are going to talk about ecology, environment and the organisms. Ecology is the study of interaction between organisms and their environment. What is an environment? Environment is the surroundings in which an organism is living. An organism is never living in an isolation. It has to interact with the organisms which are surrounding it, with the physical factors which are present around it, with the chemical factors which are present around it. So, environment consists of other living organisms, water, the air currents, the soil, maybe the roads, the cats, the dogs around us. For example, if I am an individual, organisms have to interact with their environments. For example, if I am living in an area, there are various plants present in that area. There are other human beings present in that area. There are cats and dogs. There may be microscopic organisms, the bacteria which can spoil my food, which can even make some foods for me. For example, we know that yogurt is produced by the bacteria from the milk. Every organism has to interact with its surroundings, both living surroundings and non-living surroundings. Environment provides the organism all those things which are required to live. That is food. Every organism gets food from the environment, shelter. Every organism has to get the shelter protection from the environment. For example, the human beings, which are the most advanced organisms, lives in houses. The cats and dogs, they have their own places on which they live. For example, a street. Birds live on the trees. Sometimes for bringing up their kids, they have nests. The bears and the lions have their caves in which they live. Organisms also have to interact with other organisms, which are present in the environment. So, environment is everything present in the surroundings of an organism, which is providing us, providing the organism with food, with shelter and with relationships. Environment is always changing. We know that even in a day, in a single day, temperature may change. In the morning, temperature is lower. When sun is, sun just has a rise in. When sun goes up, temperature rises up. When sun again goes down, then the temperature raises down. At night, temperature may be more different. Seasons change. Seasons winter comes, summer comes, harsh winter comes, spring, fall. Environments are always changing, even sometimes, disastrously. For example, after a flood, the environment of the area may be totally, entirely changed. After a flood, this is possible that all of the trees in a specific area are just fallen down and all the birds which were living on those trees are now homeless, just like the people of that area. So, environment sometimes may be very favorable. Sometimes it may be very hostile. That is unfavorable. What is the strategy of organisms? Organisms have to adapt to the situations. Different organisms have different properties. And according to their characteristics, their properties of life, they can survive in different types of environments. Organisms are best fit for their environment. There are different types of organisms and there are different types of environment. Every organism lives in that environment to which its characteristics are best fit. Otherwise, it will not be able to compete with other organisms of maybe the same species, maybe the different species and it will die. Or maybe it have to migrate from that area. So, each organism is best fit to its surroundings, to its environment. Every organisms always select to that environment in which its characteristics allows it to live. Otherwise, other organisms may compete with it and either it have to die or it have to migrate. Now, environment consists of two types of factors. If we generally divide them according to the living and non-living condition, we call them biotic factors and abiotic factors. Biotic factors are those factors which are living. In other words, biotic factors are the living organisms present inside the environment. The abiotic factors are all the other factors which are non-living part of the surroundings or the environment. The abiotic factors includes animals, plants, all those small animals, the small plants, the trees, the herbs, the shrubs, the shrews, the moles, very large arephans and the abiotic factors. They consist of light, air currents, the atmosphere, water, even temperature, pH, soil, all the other things present inside the environments which are non-living. The living factors or the living part of the environment may be microscopic like bacteria, viruses, which are living in the environment but they are not visible to our eyes because they are very small. But the human being can see them using a microscope just like our very small cells. So the environment consists of the biotic factors and the abiotic factors. Biotic factors are the living factors, the living organisms. Abiotic factors are all the non-living things or all the non-living surroundings. What is ecology? Ecology is from a cause and a logic. Ecology is the study of interactions of organisms with each other and with their non-living surroundings. So in ecology we study the interactions of organisms with other organisms, maybe similar organisms, maybe very different organisms and also their interactions with their non-living surroundings. For example, if a deer is living in a specific area then it have to take its food from the environment. The grasses may be the small plants whose leaves it can eat but it have to interact with the organism of same species like the other deers because in a specific area grass may be limited. If there are too many deers they have to compete with each other for food and the one who is more strong can get that food and other either have to migrate or may be die out of starvation. Those deers also have to interact with the tigers present in their area if they are present because tigers are the predators which can eat upon the deers. A deer which is living in an environment have to protect itself from the tigers or the other predators. For that it have to adapt some strategies. This also have to interact with some other animals which may be large or small. It have to drink water. If there are few water bodies and if there is a less amount of water then it have to compete even for water with other organisms. The organisms have to compete for each and everything. Their food, their shelter, for the interaction with other organisms for each and every resource which is present inside the environment. Organisms also have to interact with their abiotic factors. Like for example if temperature is so high then the organism have to protect itself from temperature. Maybe they have to find shadows, shadows of the trees if the trees are present. If the trees are not present maybe they have to find out the caves if they are present or some other type of shade or maybe they have to adapt some other strategy. So every organism have to interact with the biotic factors and the abiotic factors present in the environment. Now the biosphere. Biosphere is the whole part of earth, the planet earth which is covered with life. We say the bio, life, sphere, part of the earth, the whole part of the earth on which the living organisms are inhabiting. There are different types of areas on the earth on which the living organisms can inhabit. In water, on land and even in the air like birds. Look at a diagram. It shows that the biosphere consists of three further spheres. Actually these are not spherical but these are just for an example. These are various parts of the world of our planet earth. The atmosphere, the hydrosphere and the ecosphere. The atmosphere, the air, the hydrosphere, the waters, the ecosphere, the ecosystems. Air or atmosphere is actually part of almost all of the ecosystems. Hydrosphere or the waters, they are also parts of the ecosystems. Now what is an ecosystem? Look at another diagram. It shows various organisms in interaction with their environment. You can see a big water body on which a man is rowing a boat. On the other side, there is a large fish. You can also see various small fish. You can see various plants which are submerged in that water. Submerged means some part of them is inside the water and there are few which are totally submerged, which are totally present inside the water. There are lot many plants on the sides. There are rocks, there is an atmosphere, the air, there are clouds, there are trees. Areas like this in which different types of organisms, the animals, the plants, the bacteria, the fungi, the algae, the other organisms, they are living with their abiotic surroundings. Water, atmosphere, rocks, soil, a system in which all of these organisms are living. That is all the biotic factors are living in interaction with their abiotic factors and in interaction with each other is called an ecosystem. So ecosystem is an area in which the living organisms are living, are inhabiting in interaction with each other and with their non-living surroundings. Have a look on another diagram which also shows a mountain, a small hill with different types of trees, then there is a water body and then the big water body making a lake, then there is a stream, then there are more trees, there are different types of animals present in it and of course there is soil, there are rocks, there is an atmosphere, there are animals and there are plants. So this is an example of another wetland ecosystem. Pakistan is rich in wetland ecosystems. We have various wetlands which are very important part of Pakistan because they have diverse organisms. We say that they have a biodiversity. There are diverse forms of life present inside these ecosystems and these organisms, this biodiversity actually gives a stability to the ecosystem. They make the ecosystem stable.