Welcome dear students! Today we are going to learn about Our Environment from Class 10 Science. We have heard the word environment often being used on television, in newspapers, and by people around us. Our elders tell us that the environment is not what it used to be earlier. Others say that we should work in a healthy environment. Global summits involving developed and developing countries are regularly held to discuss environmental issues. In this chapter, we shall study how various components in the environment interact with each other and how we impact the environment.
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Let us begin with section thirteen point one, Ecosystem, What Are Its Components. All organisms such as plants, animals, microorganisms, and human beings, as well as the physical surroundings, interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. Thus, an ecosystem consists of biotic components comprising living organisms, and abiotic components comprising physical factors like temperature, rainfall, wind, soil, and minerals. For example, if you visit a garden, you will find different plants such as grasses, trees, and flower-bearing plants like rose, jasmine, and sunflower, along with animals like frogs, insects, and birds. All these living organisms interact with each other, and their growth, reproduction, and other activities are affected by the abiotic components of the ecosystem. So, a garden is an ecosystem. Other types of ecosystems are forests, ponds, and lakes. These are natural ecosystems, while gardens and crop-fields are human-made or artificial ecosystems.
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You might have seen an aquarium. Let us try to design one. What are the things we need to keep in mind when we create an aquarium? The fish would need a free space for swimming, which could be a large jar, water, oxygen, and food. We can provide oxygen through an oxygen pump, also called an aerator, and fish food available in the market. If we add a few aquatic plants and animals, it can become a self-sustaining system. Can you think how this happens? An aquarium is an example of a human-made ecosystem. Can we leave the aquarium as such after we set it up? Why does it have to be cleaned once in a while? Do we have to clean ponds or lakes in the same manner? Why or why not? We have seen in earlier classes that organisms can be grouped as producers, consumers, and decomposers according to the manner in which they obtain their sustenance from the environment. Let us recall what we have learnt through the self-sustaining ecosystem created above. Which organisms can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll? All green plants and certain bacteria which can produce food by photosynthesis come under this category and are called the producers. Organisms depend on the producers either directly or indirectly for their sustenance. These organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers, are the consumers. Consumers can be classed variously as herbivores, carnivores, omnivores, and parasites. Can you give examples for each of these categories of consumers?
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Imagine the situation where you do not clean the aquarium and some fish and plants have died. Have you ever thought what happens when an organism dies? The microorganisms, comprising bacteria and fungi, break down the dead remains and waste products of organisms. These microorganisms are the decomposers, as they break down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants. What will happen to the garbage, and dead animals and plants in their absence? Will the natural replenishment of the soil take place, even if decomposers are not there? Now let us look at Activity thirteen point two. While creating an aquarium, did you take care not to put an aquatic animal which would eat others? What would have happened otherwise? Make groups and discuss how each of the above groups of organisms are dependent on each other. Write the aquatic organisms in order of who eats whom and form a chain of at least three steps. Would you consider any one group of organisms to be of primary importance? Why or why not?
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Moving on to section thirteen point one point one, Food Chains and Webs. In our previous activity, we formed a series of organisms feeding on one another. This series of organisms taking part at various biotic levels forms a food chain. Each step or level of the 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, small carnivores or the secondary consumers at the third, and larger carnivores or the tertiary consumers form the fourth trophic level. We know that the food we eat acts as a fuel to provide us energy to do work. Thus, the interactions among various components of the environment involve the flow of energy from one component of the system to another. As we have studied, the autotrophs capture the energy present in sunlight and convert it into chemical energy. This energy supports all the activities of the living world. From autotrophs, the energy goes to the heterotrophs and decomposers. However, as we saw in the previous chapter on Sources of Energy, when one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.
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The flow of energy between various components of the environment has been extensively studied, and it has been found that the green plants in a terrestrial ecosystem capture about one percent of the energy of sunlight that falls on their leaves and convert it into food energy. When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work, and the rest goes towards growth and reproduction. An average of ten percent of the food eaten is turned into its own body and made available for the next level of consumers. Therefore, ten percent can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers. Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels. There are generally a greater number of individuals at the lower trophic levels of an ecosystem, with the greatest number being the producers. The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms, which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.
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Let me describe the figures for you since you are listening. Figure thirteen point one shows a food chain in nature, illustrating examples from a forest, a grassland, and a pond. Figure thirteen point two illustrates the different trophic levels, placing producers at the first level, primary consumers at the second, secondary consumers at the third, and tertiary consumers at the fourth. Figure thirteen point three shows a food web, consisting of many interconnected food chains, demonstrating how multiple organisms feed on each other in a complex network. Figure thirteen point four is a diagram showing the flow of energy in an ecosystem. It depicts sunlight entering the system, being captured by producers, then passing sequentially to primary consumers, secondary consumers, and finally to decomposers, with heat energy being lost at each transfer step.
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From the energy flow diagram in Figure thirteen point four, two important concepts become clear. Firstly, the flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input, and the energy which passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels, it is no longer available to the previous level. Secondly, the energy available at each trophic level gets diminished progressively due to loss of energy at each level. Another interesting aspect of the food chain is how unknowingly some harmful chemicals enter our bodies through the food chain. You have read in Class Nine how water gets polluted. One of the reasons is the use of several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies, these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, they get accumulated progressively at each trophic level.
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As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in our bodies. This phenomenon is known as biological magnification. This is the reason why our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means. Let us pause for a discussion activity. Newspaper reports about pesticide levels in ready-made food items are often seen these days, and some states have banned these products. Debate in groups the need for such bans. What do you think would be the source of pesticides in these food items? Could pesticides get into our bodies from this source through other food products too? Discuss what methods could be applied to reduce our intake of pesticides. Now let us answer the questions from this section. First, what are trophic levels? Trophic levels are each step or level of the food chain where organisms taking part at various biotic levels are placed. An example of a food chain is grass, deer, lion. The different trophic levels are the first trophic level with grass as producer, the second trophic level with deer as primary consumer, and the third trophic level with lion as secondary consumer. Second, what is the role of decomposers in the ecosystem? The role of decomposers is to break down the dead remains and waste products of organisms into simple inorganic substances that go into the soil and are used up once more by the plants, ensuring natural replenishment of the soil.
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We now move to section thirteen point two, How Do Our Activities Affect The Environment? We are an integral part of the environment. Changes in the environment affect us, and our activities change the environment around us. We have already seen in Class Nine how our activities pollute the environment. In this chapter, we shall look at two of the environmental problems in detail, that is, depletion of the ozone layer and waste disposal. Let us look at thirteen point two point one, Ozone Layer and How it is Getting Depleted. Ozone, written as O₃, is a molecule formed by three atoms of oxygen. While O₂, which we normally refer to as oxygen, is essential for all aerobic forms of life, ozone is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Ozone at the higher levels of the atmosphere is a product of ultraviolet radiation acting on oxygen molecules. The higher energy ultraviolet radiations split apart some molecular oxygen into free oxygen atoms. These atoms then combine with the molecular oxygen to form ozone as shown by the equation: O₂ plus ultraviolet radiation yields O plus O, and then O plus O₂ yields O₃.
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The amount of ozone in the atmosphere began to drop sharply in the nineteen eighties. This decrease has been linked to synthetic chemicals like chlorofluorocarbons, abbreviated as CFCs, which are used as refrigerants and in fire extinguishers. In nineteen eighty seven, the United Nations Environment Programme succeeded in forging an agreement to freeze CFC production at nineteen eighty six levels. It is now mandatory for all manufacturing companies to make CFC-free refrigerators throughout the world. Now let us perform Activity thirteen point four. Collect waste material from your homes. This could include all the waste generated during a day, like kitchen waste such as spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons, waste paper, empty medicine bottles, strips, bubble packs, old and torn clothes, and broken footwear. Bury this material in a pit in the school garden, or if there is no space available, you can collect the material in an old bucket or flower pot and cover with at least fifteen centimeters of soil. Keep this material moist and observe at fifteen day intervals. What are the materials that remain unchanged over long periods of time? What are the materials which change their form and structure over time? Of these materials that are changed, which ones change the fastest?
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Also, find out from the library, internet, or newspaper reports, which chemicals are responsible for the depletion of the ozone layer. Find out if the regulations put in place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years? We have seen in the chapter on Life Processes that the food we eat is digested by various enzymes in our body. Have you ever wondered why the same enzyme does not break down everything we eat? Enzymes are specific in their action; specific enzymes are needed for the break down of a particular substance. That is why we will not get any energy if we try to eat coal! Because of this, many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time. Substances that are broken down by biological processes are said to be biodegradable. Substances that are not broken down in this manner are said to be non-biodegradable. These substances may be inert and simply persist in the environment for a long time or may harm the various members of the ecosystem.
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Let us look at Activity thirteen point six. Use the library or internet to find out more about biodegradable and non-biodegradable substances. How long are various non-biodegradable substances expected to last in our environment? These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment. Now answer the questions. Why are some substances biodegradable and some non-biodegradable? Some substances are biodegradable because specific enzymes produced by microorganisms can break them down into simpler substances. Others are non-biodegradable because their chemical structure is not recognized by natural enzymes, so they persist without breaking down. Give any two ways in which biodegradable substances would affect the environment. First, they decompose and enrich the soil with nutrients, improving fertility. Second, if accumulated in large amounts without proper management, they can cause foul odors and breed disease-carrying organisms. Give any two ways in which non-biodegradable substances would affect the environment. First, they accumulate in landfills and water bodies, causing pollution and harming wildlife. Second, they can enter the food chain through biological magnification, causing long-term health hazards.
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Visit any town or city, and we are sure to find heaps of garbage all over the place. Visit any place of tourist interest and we are sure to find the place littered with empty food wrappers. In the earlier classes we have talked about this problem of dealing with the garbage that we generate. Let us now look at the problem a bit more deeply with Activity thirteen point seven. Find out what happens to the waste generated at home. Is there a system in place to collect this waste? Find out how the local body, such as panchayat, municipal corporation, or resident welfare association, deals with the waste. Are there mechanisms in place to treat the biodegradable and non-biodegradable wastes separately? Calculate how much waste is generated at home in a day. How much of this waste is biodegradable? Calculate how much waste is generated in the classroom in a day. How much of this waste is biodegradable? Suggest ways of dealing with this waste. Improvements in our life-style have resulted in greater amounts of waste material generation. Changes in attitude also have a role to play, with more and more things we use becoming disposable. Changes in packaging have resulted in much of our waste becoming non-biodegradable. What do you think will be the impact of these on our environment?
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Now consider Activity thirteen point eight. Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage? Find out how the local industries in your locality treat their wastes. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste? Let us think about disposable cups in trains. If you ask your parents, they will probably remember a time when tea in trains was served in plastic glasses which had to be returned to the vendor. The introduction of disposable cups was hailed as a step forward for reasons of hygiene. No one at that time perhaps thought about the impact caused by the disposal of millions of these cups on a daily basis. Some time back, kulhads, that is, disposable cups made of clay, were suggested as an alternative. But a little thought showed that making these kulhads on a large scale would result in the loss of the fertile top-soil. Now disposable paper-cups are being used. What do you think are the advantages of disposable paper-cups over disposable plastic cups? Think it over.
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Finally, Activity thirteen point nine. Search the internet or library to find out what hazardous materials have to be dealt with while disposing of electronic items. How would these materials affect the environment? Find out how plastics are recycled. Does the recycling process have any impact on the environment? Now let us answer the questions for this section. First, what is ozone and how does it affect any ecosystem? Ozone is a molecule formed by three atoms of oxygen. It shields the surface of the earth from ultraviolet radiation from the Sun. By blocking harmful ultraviolet rays, it protects living organisms from skin cancer and other radiation damage, maintaining ecological balance. Second, how can you help in reducing the problem of waste disposal? Give any two methods. First, we can segregate waste at the source into biodegradable and non-biodegradable categories for proper treatment. Second, we can reduce our use of single-use plastics and opt for reusable or biodegradable alternatives.
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Let us review what you have learnt. The various components of an ecosystem are interdependent. The producers make the energy from sunlight available to the rest of the ecosystem. There is a loss of energy as we go from one trophic level to the next, this limits the number of trophic levels in a food-chain. Human activities have an impact on the environment. The use of chemicals like CFCs has endangered the ozone layer. Since the ozone layer protects against the ultraviolet radiation from the Sun, this could damage the environment. The waste we generate may be biodegradable or non-biodegradable. The disposal of the waste we generate is causing serious environmental problems. Now we will solve the exercises completely. Exercise one: Which of the following groups contain only biodegradable items? The correct option is c, fruit-peels, cake and lime-juice. Exercise two: Which of the following constitute a food-chain? The correct option is b, grass, goat and human. Exercise three: Which of the following are environment-friendly practices? The correct option is d, all of the above, which includes carrying cloth-bags, switching off unnecessary lights and fans, and walking to school.
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Exercise four: What will happen if we kill all the organisms in one trophic level? If all organisms in one trophic level are killed, the organisms at the next higher trophic level will starve due to lack of food, and the organisms at the lower trophic level will overpopulate due to lack of predators. This will severely disrupt the ecological balance and may lead to the collapse of the entire food chain. Exercise five: Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem? Yes, the impact will be different. Removing producers will collapse the entire ecosystem as no energy enters the food chain. Removing top predators will cause herbivore overpopulation and vegetation destruction. No, organisms of any trophic level cannot be removed without causing damage to the ecosystem because all levels are interdependent for energy flow and population control. Exercise six: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem? Biological magnification is the phenomenon where harmful non-degradable chemicals like pesticides accumulate progressively at each trophic level of a food chain. Yes, the levels will be different. The concentration increases at each successive trophic level, reaching the maximum concentration at the top level occupied by humans.
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Exercise seven: What are the problems caused by the non-biodegradable wastes that we generate? Non-biodegradable wastes persist in the environment for long periods, causing land and water pollution. They block drainage systems, harm wildlife through ingestion or entanglement, enter the food chain causing biological magnification, and release toxic substances when burned, leading to air pollution and health hazards. Exercise eight: If all the waste we generate is biodegradable, will this have no impact on the environment? Even if all waste is biodegradable, it can still have an impact if generated in excessive amounts. Large accumulations can deplete oxygen during decomposition, produce foul odors, breed pathogens, and cause water and soil pollution if not managed properly. Proper composting and treatment are still necessary. Exercise nine: Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? Damage to the ozone layer is a cause for concern because it allows harmful ultraviolet radiation from the Sun to reach the Earth, which causes skin cancer, eye damage, weakens immune systems, and harms crops and marine ecosystems. Steps being taken include the nineteen eighty seven Montreal Protocol agreement to freeze and phase out CFC production, mandatory use of CFC-free refrigerants, international monitoring of ozone hole size, and public awareness campaigns to reduce ozone-depleting substances.
Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]