We have already discussed in last module about the natural resources and the flow of energy and environment. We shall now discuss in lesson 1 about our environment in more detail. The earth planet in the solar system supports life and our environment all around us affects our life every moment. This is why it is important to learn and understand in detail about our environment. All of us wish to live in a healthy ‘environment’ and we need to reflect on what we can do at our end to create a healthy environment. Global summits all over the world are regularly organized to discuss ‘environmental’ concerns.
You would be able to appreciate the significance of our environment from the fact that Dr. Rajendra K. Pachauri and his team of environmental scientists received in 2007 the Nobel peace prize for their findings on global warming and other climatic changes. Since all of us are an integral part of the environment, changes in the environment affect us and our actions affect the environment.
Our environment sustains life and as such environment consists of living forms as well as non-living factors like air, water, soil, etc. So, if you and I want to understand environment and want to preserve life on this planet Earth, we must first understand our environment and the relationship between the living and non-living factors of the environment. Next we need to reflect and act on the ways to make our environment better.
Before you start reading the objectives and other parts of the lesson, our suggestion is that you keep some, say 10, sheets of paper to complete writing parts of Activity sections of the lesson. Also prepare yourself to visit a nearby garden and a pond to observe and inquire about these ecosystems as directed in Activity sections.
It is expected that after reading lesson 1, you would be able to
The conditions that surround our surroundings are our environment. The combination of external physical conditions that affect and influence the growth, development, and survival of organisms and the complex of social and cultural conditions affecting the nature of an individual or community define our environment. So a. (All organisms like plants, animals, micro-organisms and humans etc) and b. (All non-living factors like wind, rainfall, temperature, soil and minerals etc) and their healthy or unhealthy status together define our environment. We will now discuss the focus of lesson 1.
In lesson 1 we will focus on the interaction between living and non-living components of our environment so that we are able to grasp the processes that affect its status. The relationship between the living forms and non-living factors of the environment signifies an ecosystem. In other words, you can say that ecosystem is the outcome of the interaction between environmental factors or between a. (all the living organisms) and b. (their physical surroundings).
All organisms (like plants, animals, micro-organisms and humans) and the physical surroundings interact with each other and while doing so maintain a balance in nature and thereby sustain a healthy environment. All interacting organisms in an area along with the non-living parts of the environment make an eco-system. You may like to know that the British ecologist Sir Arthur George Tansley coined in 1935 the term ecosystem and he described natural systems in “constant interchange” among their living and nonliving parts.
The ecosystem concept fits into an ordered and balanced view of nature. Scientists developed this view to simplify the study of the relationships between organisms and their physical environment. The name of this study is ecology.
As you have already learnt in an earlier module, at the top of the hierarchy is the planet’s entire living environment, known as the biosphere. Within this biosphere are several large categories of living communities known as biomes that are usually characterized by their dominant vegetation, such as grasslands, tropical forests, or deserts. The biomes are in turn made up of ecosystems. The living, or biotic, parts of an ecosystem, such as the plants, animals, and bacteria found in soil, are known as a community. The physical surroundings, or abiotic components, such as the minerals found in the soil, are known as the environment or habitat.
Let us now discuss in detail about the components of an eco-system.
An ecosystem is a system where biotic populations of species group together into communities and interact with each other and the abiotic environment. So you can say that
an eco-system comprises two components, namely, biotic and abiotic.
Biotic components are basically living organisms such as plants, animals and various kinds of microorganisms.
Abiotic components include physical factors like air, water, soil, mineral, temperature and rainfall etc.
In simple words you can say that abiotic factors are all the non-living factors while the biotic factors are all the living factors. These two components share the relationship of being dependent on each other and in this sense they constitute an ecosystem. In order to better grasp the abiotic and biotic components of an eco-system, you can carry out activity 1 before proceeding to learn about groupings of organisms.
Let us also complete Check Your Progress 1 before moving on to section 1.2.
1.2 Grouping of organisms
It is easy to see how we can categorize animals, plants and the microorganisms in the ecosystem and how do they depend upon the non-living and physical surroundings. We can group organisms as i) producers, ii) consumers and iii) decomposers according to the way they get sustenance from the environment.
With the help of sunlight, carbon dioxide, water, and minerals as well as a very unique pigment called the chlorophyll; green plants prepare their food by the process of photosynthesis. Green plants prepare food by utilizing the above-mentioned natural resources (sunlight, carbon dioxide, water and minerals) by the process of photosynthesis. So the producers of the food on the planet of earth are the green plants and certain blue-green algae. They produce food by making organic compounds like sugar and starch from inorganic substances using the radiant energy of the sun. The green plants and blue-green algae are the sources of food for most animals. Most organisms depend directly or indirectly on the producers for their sustenance. You can categorize the green plants and the animals in the different categories depending on their relationship. Green plants are in the group of producers. They produce the food for the entire population.
Animals, that eat the green plants or producers, are in the group of consumers. Organisms that get their energy by consuming organic substances are called heterotrophs. Heterotrophs include herbivores, which obtain their energy by consuming live plants; carnivores, which obtain energy from consuming live animals.
You can also classify consumers into groups such as herbivore (who lives by consuming green plants and grasses only), carnivore (who survives by eating meat only), omnivore (surviving on both green plants and meat) and parasite (living in or on another organism and getting its food from that organism). Depending on the kind of food they feed on you can divide consumers into a) primary consumers, b) secondary consumers and c) tertiary consumers and so on.
c) Tertiary consumers are those who feed on secondary consumers. For example, snake.
On death of an organism begins the process of decomposition in which the microorganisms, comprising bacteria and fungi, breakdown the dead remains and waste products of organisms. These microorganisms are the decomposers. Detritivores, scavengers and decomposers consume dead biomass.
The decomposers breakdown the complex organic substances into simple inorganic substances and these substances get mixed into the soil. Once in the soil, plants use them once more to produce food. This is how the cycle of production, consumption and decomposition goes on to sustain life in our environment. You can describe the cycle better in terms of the series of food chains and webs.
Food chains and webs or food networks describe the feeding relationships between species to another within an ecosystem. Organisms are connected to the organisms they consume. Please note that typically a food chain or food web refers to a graph where only connections are recorded, and a food network or ecosystem network refers to a network where the connections are given weights representing the quantity of nutrients or energy being transferred.
Let us also complete Check Your Progress 2 before moving on to section 1.3
A food chain is the flow of energy from one organism to the next. Let us now see whether we can draw a relationship between the producers, consumers and decomposers, in order of who eats whom. Yes, we can draw a relationship between producers and consumers on the basis of who eats whom. This is called a food chain. What is a food chain?
Food chain is a relationship between various components of an ecosystem on the basis of who eats whom. For example, you may have noticed that grasshopper eats green plants and frog consumes grasshopper and snake eats frog and bird finally eats snake. Can we categorize this food chain in terms of producers and consumers? Yes, we can do so.
You can call green plants producers while insect (grasshopper), frog, snake and bird, all fall in the category of consumers. Insects since they feed directly on the producers are primary consumers and frogs are secondary consumers and similarly, snakes are tertiary consumers and birds are quaternary consumers. This is an example of a relationship between various biotic components of an ecosystem. This relationship represents a series of organisms feeding on one another. Organisms taking part at various biotic levels compose a food chain. Figure 1.1 shows you a food chain in nature, a) in forest and b) in grassland.
On the basis of this figure, in your Activity 2 you can make a figure to show a food chain in a natural pond.
In the ecosystem we have just discussed examples of three food chains. There can be many food chains existing in the ecosystem and these food chains may be interrelated, that is, at producer level there are similar plants that may be eaten at one level by many consumers. That is, plant is the same, but the consumer levels are different. At the top consumer level we find the similar consumers can be part of many food chains, which are interrelated in their intermediate levels of the primary consumers and secondary consumers. Such interrelated food chains may find the common producer and the common topmost consumer, forming a food web. So many food chains are interrelated in the ecosystem and their interrelationships make a food web.
In order to understand in detail the formation of a food chain, we need to talk in the sub-section 1.3.1 about each step of this process.
Let us also complete Check Your Progress 3 before moving on to section 1.3.1
1.3.1 Trophic levels
Organisms in a food chain are grouped into trophic levels — from the Greek word for nourishment, trophikos — based on how many links they are removed from the primary producers. Trophic levels may consist of either a single species or a group of species that are presumed to share both predators and prey. They usually start with a primary producer and end with a carnivore.
Each step or level of food chain forms a trophic level. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second level. Small carnivores or the secondary consumers are at the third level while larger carnivores or the tertiary consumers come at the fourth trophic level. Finally, the fifth trophic level consists of the decomposers, organisms such as fungi and bacteria that break down dead or dying matter into nutrients that can be used again.
It is often the case that biomass of each trophic level decreases from the base of the chain to the top. This is because energy is lost to the environment with each transfer. Graphic representations of the biomass or productivity at each trophic level are called trophic pyramids.
can better understand the various trophic levels by looking at the Figure.
On the basis of your understanding of series of food chain so far learnt in this lesson, carry out Activity 3 before reading more about food chains in different ecosystems.
You know that the food we consume works as a fuel to give us energy to do work. In other words, the interactions among various parts of our environment make possible flow of energy from one part of the system to another. You have learnt above that the plants or autotrophs capture the energy available in sunlight and convert it into chemical energy. This energy provides support to all the activities of the living-beings. From autotrophs or plants, the energy goes to the consumers and decomposers. You have already learnt in an earlier module that when one form of energy turns into another, there occurs loss of some energy to the environment in non-usable forms. It means that it is not possible to have a very long food chain.
Let us also complete Check Your Progress 4 before moving on to section 1.3.2
As you know that in the food chain a very important process takes place, that is, the transfer of food from one level to another. The transfer of energy takes place from one food level, that is, one trophic level to the next trophic level. So what happens as per the rule of the thermodynamics (or the relations between heat and other forms of energy involved in physical and chemical processes), the transfer of energy is never efficient, that is, whenever energy is transferred from one system to another, that is, from one trophic level to another, hundred percent transfer is not possible because large amount of energy gets wasted. Some energy and/or biomass is lost at each stage of the food chain as; faeces (solid waste), movement energy and heat energy (especially by birds and mammals). Therefore, only a small amount of energy and biomass is incorporated into consumer's body and transferred to the next feeding level, thus showing a pyramid of biomass
Only a very small amount of energy, calculated as ten percent energy, is transferred from one to the next trophic level. As mentioned above, when primary consumers eat green plants, there occurs a loss of energy as heat to environment, some amount goes into digestion and in doing work and the rest goes in growing up and reproduction. So only an average of ten percent of the food consumed stores in one’s body and the next level of consumers can use only this amount of energy. You can take this ten percent energy as the average value for the amount of organic matter that the next level of consumer can receive at each step of transfer of energy. So you can say that on average, only ten per cent of the organism's energy is passed on to its predator. The other ninety per cent is used for the organisms life processes or is lost as heat to the environment.
So, if we go as per the ten percent law, we find that whatever the energy is transferred, from that only ten percent gets transferred and as it happens, by the time the energy reaches the last trophic level the amount of energy which is left for the last consumer is so less that it is absolutely negligible. That is why nature does not allow a very long food chain. The maximum it can have is seven levels or generally it has four or five levels. The loss of energy is really so much that very small amount of usable energy remains available after four trophic levels.
There are usually a greater number of individuals at the lower trophic levels of an ecosystem. The greatest number in an ecosystem consists of the producers.
Food chains are overly simplistic as representatives of what typically happens in nature. The food chain shows only one pathway of energy and material transfer. Most consumers feed on multiple species and are, in turn, fed upon by multiple other species. The relations of detritivores and parasites are seldom adequately characterized in such chains as well. Usually the food chain has a producer, consumer, herbivore, carnivore, omnivore, and decomposer.
This is why it is easy to make that the length and complexity of food chains vary greatly. Two or more other kinds of organisms eat an organism and in turn several other organisms eat them and instead of a straight-line food chain, the relationship among the organisms is generally a series of branching lines. We call this series a food web.
A food web extends the food chain concept from a simple linear pathway to a complex network of interactions. Victor Summerhayes and Charles Elton in 1923 and Hardy in 1924 published the earliest food webs. Summerhayes and Elton depicted the interactions of plants, animals and bacteria on Bear Island, Norway, while Hardy's food web showed the interactions of herring and plankton in the North Sea. Figures 1.3 shows you a food web of many food chains. Food sources of most species in an ecosystem are much more diverse, resulting in a complex web of relationships than shown in the figure below.
Energy enters the food chain from the sun. The flow of energy is unidirectional. It means that the energy captured by the autotrophs or green plants does not revert back to the solar input and the energy which herbivores or primary consumers capture does not come back to green plants or the producers. As the energy moves progressively through the various trophic levels, it is no longer available to the previous level. Figure 1.4 illustrates the unidirectional mode of energy flow.
Figure 1.4 Energy Flow
Let us also complete Check Your Progress 5 before moving on to section 1.4
1.4 Disturbances in food chains or impact of human-made activities on our environment
With the increasing industrialization and with the needs of the expanding and increasing population, human-made activities disturb the food chain somewhere or the other. Yes, many human-made activities are negatively affecting the food chains in one or other way. Let us now look at the ways by which human-made activities are disturbing the food chain.
Take the example of the excessive use of pesticides by the farmers. This is a human-made activity, affecting ecosystem as well as the environment. Let us describe how increasing or excessive use of pesticides is disturbing the life or food chain in the ecosystem. This is resulting into a phenomenon, called biomagnification.
1.4.1 Process of bio-magnification
Through the process of bio-magnification unknowingly some harmful chemicals enter our bodies through food chain. These chemicals wash down into the soil or into the water bodies. From the soil, plants absorb them along with water and minerals, and similarly, from the water bodies aquatic plants and animals consume these chemicals. This is one of the ways in which chemicals enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. Then the amount of pesticides or chemicals increases in each of the trophic levels. This process is known as bio-magnification.
Bio-magnification is an increased amount of the pesticides at each successive trophic level. The process may end in a lethal level to the consumers. When farmers are using pesticides in their field, the excessive pesticides may be washed away with the water and may go into other water bodies and may mix with the water and contaminate the water. This water may be used by the phytoplankton in making their bodies through their food. So, the contaminated pesticides enter in their body. Suppose two to three small fish eat ten to fifteen phytoplanktons, the entire accumulated amount of ten to fifteen phytoplanktons would reach in the body of the two or three small fish. If big fish eat the small fish and in turn the birds eat the big fish, then ten to fifteen phytoplanktons, consumed initially by the small fish would enter the body of the topmost single consumer. This may result into an increased amount and prove to be lethal limit and cause the death. This was the process, observed long back in the case of pelican birds in the Michigan Lake. They died because of the increased concentration of the pesticide. This pesticide was DDT and pelicans died because of the process of bio-magnification of DDT in their bodies. The increase in the amount of the pesticides in the water sample is biomagnification or bioaccumulation. Because of this process, we find that our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues. We cannot always remove these residues by washing or other means.
Let us also complete Check Your Progress 6 before moving on to section 1.4.2
1.4.2 Process of desertification
Another effect of human-made activities on our environment is desertification. Desertification occurs when there is some disturbance in food chain at any of the trophic level. If in any food chain primary consumers eat green plants and secondary consumers eat primary consumers and so on and this goes on without application of a judicious system of usage, the result will be that the green plants will become extinct. You know that people are cutting trees at an alarming rate for making room to build houses, factories and offices. Cleaning up of the land by cutting the green plants will mean that there will be no producers any more. In that case primary consumers will not get any food because of the extinction, cutting away of the green plants. Consequently secondary and tertiary consumers will also not get any food and eventually they too will die or become extinct. All this will occur due to a disturbance in food chain. Gradually the area, which was a green lush area, will become a kind of a desert. Desertification will clearly be the effect of man-made activity.
So far you learnt about what goes on within the world of living-beings. But we have not yet explicitly talked about the role of abiotic components of an ecosystem in birth, growth and survival of the various organisms. Without understanding this process, understanding of our environment remains incomplete.
Any given place may have several different ecosystems that vary in size and complexity. A tropical island, for example, may have a rain forest ecosystem that covers hundreds of square miles, a mangrove swamp ecosystem along the coast, and an underwater coral reef ecosystem. No matter how the size or complexity of an ecosystem is characterized, all ecosystems exhibit a constant exchange of matter and energy between the biotic and abiotic community. Ecosystem components are so interconnected that a change in any one component of an ecosystem will cause subsequent changes throughout the system.
Abiotic components play their role in the process when biotic components like green plants prepare food by drawing energy from abiotic sources. That is the green plants prepare their food with the help of carbon dioxide, water, minerals and chlorophyll. These you can say are abiotic factors coming into play. Green plants prepare their food by utilizing the abiotic factors and once they become the producers they serve as the source of the food for the next trophic level of the food chain and this way the food chain functions.
After these producers and consumers die, another set of organisms called the decomposers play their role. After the death of insects, birds and snakes (whatever category they belong to) decomposers feed on the dead bodies and then release minerals and chemicals from their body. This is how they play a very important role in regulating biogeochemical cycle.
Biogeochemical cycle as the name suggests is the bio, geo, and chemical cycle. Bio pertains to living, geo pertains to the earth and chemicals refer to the minerals. So, biogeochemical cycle means all the minerals, which are used up by the green plants in making up their body.
All the chemicals that the green plants use in making their body from the natural resources go back again to mineral pool of the earth but in a cyclic manner. As we learnt earlier in the lesson, the plants or producers, when they are eaten up the consumers and when the consumers die, they are decomposed by a set of organisms which are called as decomposers. Decomposers utilize the decomposed organic substances of a consumer’s body and then they release the minerals or chemicals that go back to the mineral pool, where the plant grows. The new plants can utilize these chemicals to make up the new body, and its new body once again gets into the cycle.
This is the way you can comprehend the nature of relationship between biotic and abiotic components of the ecosystem.
As mentioned earlier, we need to reflect on the ways to create a healthier environment for our next generation and us. Section 1.4 of this lesson included details on how human-made activities affect our environment. There we mentioned only negative impact of human-made activities on the environment. Surely, there can be ways to improve the current status of our environment by carrying out certain positive activities to improve and make it healthier to live in. This is a vast subject and many environmental scientists are busy in finding out more and more ways of reducing the negative impact and promoting the positive attitude and practices to save our environment. Here, we will touch upon only those steps that we can take at our end in both reflecting and acting in positive ways to better manage and preserve our environment. Contribution of every single person will go a long way in making our environment healthy.
We can begin with our homes. For example, you can try to follow the practices listed below.
Recycle everything: newspapers, bottles and cans, aluminum foil, etc.
Store food in re-usable containers.
Let us look at the amount of waste we generate in our homes and schools and then find out about the prevailing system of waste collection. Then the question would come up if there is any mechanism to sort out bio-degradable matter and non-bio-degradable matter in the total body of waste material. The next question would be to look for a mechanism to treat the two types of waste material separately. These are not very easy tasks to undertake but if you have fully understood the learning points of lesson 1, our expectation is that you will at least reflect on these questions and then take some concrete actions to address them at a concrete level.
Since environmental concerns touch all of us, it is always a good idea to form a group to work on environmental problems. If your individual actions are part of a wider movement to create a healthier environment, even your tiny efforts will bear more fruits in terms of their visibility and deeper impact.
If as a user of innumerable consumption items you take care to purchase only environment friendly goods and avoid anti-environment items like a bad virus, you will protect our environment in numerous ways.
Similarly, if you take care to segregate your waste material at home and school into bio-degradable and non-bio-degradable items and then your group of activists can initiate the action to set up with the help of local government and school authorities some mechanisms of treating both types of waste material into re-usable forms, you would be making efforts to save our environment.
If you make sure that you avoid the use of non-bio-degradable plastic and alternatively use paper or cloth bags to carry your purchases from shops to home, you would be avoiding use of plastic carry bags. You would have noticed that now vendors serve beverages in trains in India in disposable paper cups which are both hygienic and cost-effective.
We can keep on adding several more activities that you and I can undertake to improve the health of our environment. Let us now complete Check Your Progress 7 as the last task of lesson 1. In addition, let us all hope for better health status of our environment,
Let us also complete Check Your Progress 7 before completing study of lesson I