UNIT-15 OUR ENVIRONMENT
Environment: Our surrounding is called environment.
ECOSYSTEM;- This is a system of interdependencies among various living beings and non-living things in a given habitat.
Components of Ecosystem
An ecosystem has two types of components, viz. biotic component and abiotic component.
Abiotic Component
All the non-living things make the abiotic component of an ecosystem. Air, water and soil are the abiotic components. Air provides oxygen (for respiration), carbon dioxide (for photosynthesis) and other gases for various needs of the living beings.
Water is essential for all living beings because all the metabolic activities happen in the presence of water. Soil is the reservoir of various nutrients which are utilised by plants. Through plants, these nutrients reach other living beings.
Biotic Component
All living beings make the biotic component of an ecosystem. Green plants play the role of producers; because they prepare the food by photosynthesis. Animals and other living beings play the role of consumers; because they take food (directly or indirectly) from plants. Bacteria and fungi play the role of decomposers; as they decompose dead remains of plants and animals so that raw materials of organisms can be channelized back to the environment.
FOOD CHAIN
A food chain is a simple representation of transfer of energy from the sun to different biotic components of an ecosystem. Sun is the ultimate source of energy. Green plants convert solar energy into chemical energy during photosynthesis. When an animal takes food, this energy is supplied to the animal and the process goes on. A simple food chain can be shown as follows:
Producer → Primary Consumer → Secondary Consumer
FOOD WEB
Real life cannot be as simple as a food chain shown above. In any ecosystem, there can be many food chains which are interlinked at various levels. Thus, many food chains form a network which is called food web.
TRANSFER OF ENERGY THROUGH A FOOD CHAIN
Different levels in the food chain are called trophic level. Out of the energy consumed by an organism at a particular trophic level, 90% is utilised for its own need and rest 10% is left for the organism of the next trophic level. So, very little energy is left for the organism which is at the tertiary level. Let us assume that a green plant makes 100% energy in the form of chemical energy. 90% of this energy would be utilised for its own purpose. This would leave just 10% energy for the primary consumer. Now, primary consumer shall also utilize 90% of energy which was consumed by it. This would leave just 1% energy for (10% of 10 = 1) for the secondary consumer. By this logic, the tertiary consumer would get just 0.1% of energy which was originally made by the green plant. This is the reason, there can be just one or two organisms at the top of the food pyramid. This explains why the population of producers is always the largest in an ecosystem; followed by the population of herbivores and then that of carnivores. Moreover, an herbivore needs to eat many plants in its lifetime to fulfill its energy need. Similarly, a carnivore needs to eat many herbivores in its lifetime.
BALANCE IN THE ECOSYSTEM
There is a delicate balance in an ecosystem; as far as number of organisms at a particular trophic level is concerned. An increase or decrease in population of any organism can disturb this balance. Let us take a hypothetical example to understand this. If all the deer are killed in a jungle, the lions would be left with no food. This would endanger the existence of lions. Once the lions and deer would be finished, it would result in population explosion of green plants. If all the lions die in a jungle, it would create another problem. Since no lion would be left to kill the deer, the population of deer would increase substantially. This will finish off all the green plants and finally even the deer would be left with no food for them.
Biodegradable Substance: Substances which can be decomposed by microorganisms are called biodegradable substances. All the organic substances are biodegradable.
Non-biodegradable: Substances which cannot be decomposed by microorganisms are non-biodegradable. All inorganic substances are non-biodegradable. Many synthetic substances are also non-biodegradable.
OZONE LAYER DEPLETION:
Ozone layer is also known as stratosphere. When ultraviolet radiations act on oxygen, the oxygen gets converted into ozone.
Ozone layer works like a protective shield for living beings. The ozone layers wards off harmful ultraviolet radiations from the sun.
Effect of CFCs: Use of CFCs (Chlorofluorocarbon) has damaged the ozone layer. As a result, the ozone layer has become thinner at certain parts. In 1987, the UNEP (United Nations Environment Programme) succeeded in forging an agreement among different nations to freeze the CFC production at 1986 level. Later, an agreement was signed among different nations to phase out CFCs. It is important to note that CFC is used in refrigerators and aerosol spray. India is also a signatory of that agreement and thanks to the efforts by the United Nations and different environmentalists, the CFC emission has been put under some control.
Problems of Waste Disposal: During our day to day activities, we produce lot of waste. While some of the waste is biodegradable, a large chunk is composed of non-biodegradable substances. Plastic waste is a serious concern because plastic is non-biodegradable. We need to respect our environment and find out ways to reduce the burden on our environment.
TEXTUAL QUESTIONS
1. Why are some substances biodegradable and some non-biodegradable?
Answer-Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.
Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.
Answer-Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.
Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.
2. Give any two ways in which biodegradable substances would affect the environment.
Answer-Biodegradable substances affect the environment by:
→ The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.
→ The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer-Non-biodegradable substances affect the environment by:
→ They contaminate soil and water resources as they cannot be decomposed by micro-organisms.
→ These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer-The various links or steps in a food chain at which the transfer of food and energy takes place are called trophic levels.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.
Answer-Biodegradable substances affect the environment by:
→ The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.
→ The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer-Non-biodegradable substances affect the environment by:
→ They contaminate soil and water resources as they cannot be decomposed by micro-organisms.
→ These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer-The various links or steps in a food chain at which the transfer of food and energy takes place are called trophic levels.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.
In the above fig. Grass is the producer which is eaten by the grasshooper known as primary consumer. Then the grasshooper is eaten by shrew, secondary consumer and lastly shrew eaten up by owl, tertiary conusmer.
2. What is the role of decomposers in the ecosystem?
Answer-Various role played by decomposers in the ecosystem are:
→ They clean the environment. → They decompose biodegradable substances into useful substances.
Answer-Various role played by decomposers in the ecosystem are:
→ They clean the environment. → They decompose biodegradable substances into useful substances.
→ They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.
→ They maintain the nutrient pool by returning back the nutrients in the pool.
1. What is ozone and how does it affect any ecosystem?
Answer-Ozone (O3) is a molecule, made up of three atoms of oxygen.
Ozone (O3) forms a layer in the upper atmosphere. It is very essential for the life on this planet. It shields the surface of the earth from ultra-violet radiation (UV) coming from sun as these radiations are very harmful causing skin cancer and cataract in humans. It also does harm to the crops.
2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer-We can help in reducing the problem of waste disposal by these methods:
→ By separating biodegradable substances from non-biodegradable substances.
→ By reducing, reusing and recycling non-biodegradable substances.
Excercise
1. Which of the following groups contain only biodegradable items? (d) Cake, wood and grass
2. Which of the following constitute a food-chain? (b) Grass, goat and human
3. Which of the following are environment-friendly practices? (d) All of the above
→ They maintain the nutrient pool by returning back the nutrients in the pool.
1. What is ozone and how does it affect any ecosystem?
Answer-Ozone (O3) is a molecule, made up of three atoms of oxygen.
Ozone (O3) forms a layer in the upper atmosphere. It is very essential for the life on this planet. It shields the surface of the earth from ultra-violet radiation (UV) coming from sun as these radiations are very harmful causing skin cancer and cataract in humans. It also does harm to the crops.
2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer-We can help in reducing the problem of waste disposal by these methods:
→ By separating biodegradable substances from non-biodegradable substances.
→ By reducing, reusing and recycling non-biodegradable substances.
Excercise
1. Which of the following groups contain only biodegradable items? (d) Cake, wood and grass
2. Which of the following constitute a food-chain? (b) Grass, goat and human
3. Which of the following are environment-friendly practices? (d) All of the above
4. What will happen if we kill all the organisms in one trophic level?
Answer-If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an Example, In a food chain Grass → Dear → Lion, If we remove all lions then population of deer will increase which will cause over-grazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.
5. 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?
Answer-If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an Example, In a food chain Grass → Dear → Lion, If we remove all lions then population of deer will increase which will cause over-grazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.
5. 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?
Answer-Impact of removing all organisms of a trophic level is different for different trophic levels.
For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can't remove any trophic level without causing damage to the ecosystem as one is dependent on other for their survival. If we remove any one this will create imbalnce in the ecosystem.
6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can't remove any trophic level without causing damage to the ecosystem as one is dependent on other for their survival. If we remove any one this will create imbalnce in the ecosystem.
6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer-Biological magnification is defined as the phenomena of accumulation or increase in the concentration of some toxic substances at each trophic level.
The levels of biomagnification will be different at different trophic levels. For example, in a pond of water, DDT was sprayed and the producers were found to have 0.04 ppm concentration of DDT. Since many types of planktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as one sea gull eats many clams. Hawk, the top carnivore, has the highest concentration of DDT.
7. What are the problems caused by the non-biodegradable wastes that we generate?
Answer-The problems caused by non-biodegradable wastes are:
→ The cause biomagnification.
→ They increase pollution.
→ They make environment unclean.
→ They kill useful microorganisms.
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer-If all the waste generated would be biodegradable this will also create problem. As the numbers of decomposers will be quite low so wastes cannot be broken down into harmless simpler substance at right time. It will became breeding ground for flies causing spread of diseases. It will also emits foul smell which makes the life of people miserable.
Answer-The problems caused by non-biodegradable wastes are:
→ The cause biomagnification.
→ They increase pollution.
→ They make environment unclean.
→ They kill useful microorganisms.
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer-If all the waste generated would be biodegradable this will also create problem. As the numbers of decomposers will be quite low so wastes cannot be broken down into harmless simpler substance at right time. It will became breeding ground for flies causing spread of diseases. It will also emits foul smell which makes the life of people miserable.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer-The damage to the ozone layer a cause for concern because:
→ It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
→ It can result in the death of many phytoplanktons that leads to increased global warming.
→ It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
→ It can result in the death of many phytoplanktons that leads to increased global warming.
To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.
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