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Chapter 15: Our Environment
The term 'environment' is widely used to refer to the surroundings in which we live. Our environment encompasses everything around us, and there is a constant interaction between living organisms and their physical surroundings. Understanding these interactions and how human activities impact the environment is crucial in addressing contemporary environmental challenges.
Eco-System — What Are Its Components?
All living organisms (plants, animals, microorganisms, humans) interact with each other and their non-living environment. This interaction creates and maintains a balance in nature. An ecosystem is a functional unit comprising all the interacting organisms in a specific area, together with the non-living constituents of their environment.
An ecosystem has two main components:
- Biotic components: All living organisms (e.g., plants, animals, bacteria, fungi).
- Abiotic components: The non-living physical factors of the environment (e.g., temperature, rainfall, wind, soil, minerals, sunlight).
Examples of ecosystems include forests, ponds, lakes (natural ecosystems), and gardens, crop-fields, aquariums (human-made or artificial ecosystems).
In an ecosystem, organisms can be grouped based on how they obtain their food and energy:
- Producers: Organisms that produce their own food from inorganic substances using energy (usually sunlight). Green plants and some bacteria are producers (autotrophs). They form the base of every ecosystem.
- Consumers: Organisms that obtain food by consuming other organisms. They depend on producers either directly or indirectly. Consumers can be herbivores (eat plants), carnivores (eat animals), omnivores (eat both plants and animals), or parasites (live on or in other organisms and derive food from them).
- Decomposers: Microorganisms (bacteria and fungi) that break down the dead remains and waste products of organisms into simple inorganic substances. These simple substances are then released back into the soil and are used by producers. Decomposers are essential for nutrient cycling and preventing the accumulation of dead organic matter.
In an ecosystem, there is interdependence among these groups. Producers make energy available, consumers feed on them or other consumers, and decomposers recycle nutrients from dead organisms and waste.
Food Chains And Webs
The flow of energy and matter in an ecosystem occurs through feeding relationships between organisms.
A food chain is a linear sequence of organisms where energy is transferred from one organism to the next as one organism eats another. It shows 'who eats whom'. Each step or level in a food chain is called a trophic level.
Trophic Levels:
- First trophic level: Producers (autotrophs) – capture solar energy (e.g., plants, algae).
- Second trophic level: Primary consumers (herbivores) – eat producers (e.g., deer, rabbit, grasshopper).
- Third trophic level: Secondary consumers (small carnivores or omnivores) – eat primary consumers (e.g., snake, bird, frog).
- Fourth trophic level: Tertiary consumers (larger carnivores) – eat secondary consumers (e.g., eagle, lion).
Energy flow through trophic levels:
- Producers capture solar energy (about 1% of sunlight falling on leaves in terrestrial ecosystems).
- When energy is transferred from one trophic level to the next, a significant amount is lost as heat to the environment, used for metabolic activities, or remains in undigested matter. Only about 10% of the energy available at one trophic level is transferred to the next trophic level. This is the 10% Law of Energy Transfer.
Because so much energy is lost at each step, food chains are typically short, consisting of only three or four trophic levels. Longer food chains are not sustainable due to insufficient usable energy at higher levels.
The flow of energy in an ecosystem is always unidirectional (from producers to consumers) and progressively diminished at each step.
In reality, feeding relationships are more complex than simple linear food chains. Organisms are often eaten by multiple other organisms. A food web shows interconnected food chains, forming a network of feeding relationships in an ecosystem.
Biological Magnification (Biomagnification): Unknowingly, harmful chemicals can enter our bodies through the food chain. Pesticides and other non-degradable chemicals used in agriculture or released into water bodies are absorbed by plants and aquatic organisms and enter food chains. These chemicals are not broken down and accumulate progressively at each trophic level. Since humans often occupy the top trophic levels, the maximum concentration of these harmful chemicals accumulates in human bodies. This increasing concentration of non-biodegradable substances at successive trophic levels is called biological magnification. This is why food products can contain pesticide residues.
How Do Our Activities Affect The Environment?
Humans are an integral part of the environment, and our activities have a significant impact on the environment around us. These impacts can be both positive and negative, but increasingly, human activities are leading to environmental problems.
Two significant environmental problems caused by human activities are the depletion of the ozone layer and the management of waste we produce.
Ozone Layer And How It Is Getting Depleted
Ozone (O₃) is a molecule made of three oxygen atoms. While ozone is poisonous at ground level, the ozone layer in the upper atmosphere (stratosphere) is vital for life.
The ozone layer acts as a natural shield, protecting the Earth's surface from harmful ultraviolet (UV) radiation from the Sun. UV radiation is highly damaging to living organisms, causing problems like skin cancer in humans.
Ozone in the stratosphere is formed when high-energy UV radiation splits molecular oxygen ($\text{O}_2$) into individual oxygen atoms (O). These free oxygen atoms then combine with oxygen molecules to form ozone ($\text{O}_3$).
$\text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O}$
$\text{O} + \text{O}_2 \longrightarrow \text{O}_3$
The amount of ozone in the atmosphere started decreasing sharply in the 1980s, leading to the formation of an 'ozone hole' over Antarctica. This depletion is linked to human-made chemicals, particularly chlorofluorocarbons (CFCs). CFCs were widely used as refrigerants, propellants in aerosols, and in fire extinguishers. These chemicals are very stable and persist in the atmosphere, eventually reaching the stratosphere where they react with and destroy ozone molecules.
International agreements, such as the UNEP agreement in 1987, have been implemented to reduce and phase out the production and use of CFCs globally. Monitoring the size of the ozone hole indicates whether these measures are effectively reducing damage to the ozone layer.
Managing The Garbage We Produce
In our daily lives, we generate a significant amount of waste material. The management and disposal of this garbage pose a major environmental challenge.
The waste we generate can be broadly classified into two types:
- Biodegradable waste: Substances that can be broken down into simpler, harmless substances by biological processes, mainly by microorganisms (bacteria and fungi). Examples: kitchen waste (food scraps, vegetable peels), paper, cotton cloth, wood. Enzymes produced by microorganisms are specific in breaking down substances. Natural enzymes cannot break down many human-made materials.
- Non-biodegradable waste: Substances that are not broken down by biological processes and persist in the environment for a long time. Examples: plastics, synthetic fibres, metals, glass, electronic waste (e-waste). These materials can accumulate in the environment, causing pollution, harming ecosystems, and entering food chains.
Impacts of Waste:
- Accumulation of garbage leads to pollution of land, water, and air (through decomposition gases).
- Non-biodegradable wastes clog drains, harm wildlife (e.g., animals eating plastic), contaminate soil and water, and persist for very long periods.
- Improper waste disposal can spread diseases.
- Production processes for many materials (especially non-biodegradable ones) can also cause environmental damage.
Managing garbage requires effective systems for collection, segregation (separating biodegradable and non-biodegradable waste), treatment (e.g., composting for biodegradable waste, recycling or safe disposal for non-biodegradable waste), and safe disposal. Changes in lifestyle towards reducing waste generation (e.g., using cloth bags instead of plastic bags, carrying own water bottles), reusing items, and recycling are crucial steps in addressing the problem of waste disposal.
Improvements in packaging have often led to increased use of disposable and non-biodegradable materials (like multi-layered plastics), exacerbating the waste problem.
Intext Questions
Page No. 260
Question 1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
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Question 2. What is the role of decomposers in the ecosystem?
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Page No. 262
Question 1. Why are some substances biodegradable and some non-biodegradable?
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Question 2. Give any two ways in which biodegradable substances would affect the environment.
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Question 3. Give any two ways in which non-biodegradable substances would affect the environment.
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Page No. 264
Question 1. What is ozone and how does it affect any ecosystem?
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Question 2. How can you help in reducing the problem of waste disposal? Give any two methods.
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Exercises
Question 1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
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Question 2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
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Question 3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
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Question 4. What will happen if we kill all the organisms in one trophic level?
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Question 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?
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Question 6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
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Question 7. What are the problems caused by the non-biodegradable wastes that we generate?
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Question 8. If all the waste we generate is biodegradable, will this have no impact on the environment?
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Question 9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
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