Eco-System — What Are Its Components?

All interacting organisms (plants, animals, microorganisms, humans) and the non-living physical surroundings in a specific area form an **ecosystem**. Ecosystems maintain a balance in nature through the interactions between their components. An ecosystem consists of two main components:

• **Biotic components:** All living organisms (producers, consumers, decomposers).
• **Abiotic components:** The non-living physical factors of the environment (temperature, rainfall, wind, soil, minerals, sunlight, water, etc.).

Living organisms in an ecosystem are influenced by the abiotic factors, and they interact with each other, forming relationships like feeding on one another.

Examples of ecosystems include natural ecosystems like forests, ponds, and lakes, and human-made (artificial) ecosystems like gardens, crop-fields, and aquariums.

Within an ecosystem, organisms are classified based on how they obtain their sustenance:

• **Producers:** Organisms (like green plants and some bacteria) that produce their own food (organic compounds) from simple inorganic substances (CO$_2$, water) using an external energy source (like sunlight) through photosynthesis. They make energy available for the rest of the ecosystem.
• **Consumers:** Organisms that obtain energy by consuming food produced by producers or by feeding on other consumers. Consumers are classified as herbivores (eat plants), carnivores (eat animals), omnivores (eat both plants and animals), and parasites (live on or inside other organisms, deriving nutrition from them).
• **Decomposers:** Microorganisms (like bacteria and fungi) that break down the dead remains and waste products of organisms. They convert complex organic substances into simple inorganic substances (nutrients) that return to the soil or water and are used by producers. Decomposers play a vital role in nutrient cycling and cleaning the environment by breaking down dead matter. Without them, nutrients would be locked up in dead organisms, and natural replenishment of the soil would not occur efficiently.

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Food Chains And Webs

In an ecosystem, organisms are linked through feeding relationships, forming **food chains**. A food chain shows the flow of energy from one organism to the next as one organism is eaten by another.

Example of a simple food chain: Grass $\to$ Deer $\to$ Lion.

Each step or level in a food chain where energy is transferred is called a **trophic level**.

• First trophic level: **Producers** (Autotrophs like plants). They capture solar energy.
• Second trophic level: **Primary consumers** (Herbivores) that feed directly on producers.
• Third trophic level: **Secondary consumers** (Small carnivores or omnivores) that feed on primary consumers.
• Fourth trophic level: **Tertiary consumers** (Larger carnivores) that feed on secondary consumers. Higher levels (quaternary, etc.) are possible but less common.

Energy flows through an ecosystem from producers to consumers and decomposers. Only about **1% of the sunlight** falling on leaves is captured by producers. When energy is transferred from one trophic level to the next, only about **10% of the energy** from the previous level is available to the next level. The remaining 90% is lost as heat to the environment, used for digestion, or expended in life processes like growth and reproduction.

This **10% Law** means that energy available at each successive trophic level decreases significantly. Due to this large energy loss, food chains typically consist of only three or four steps, as very little usable energy remains beyond that.

Food chains are often interconnected, forming complex networks called **food webs**. Most organisms are eaten by multiple types of other organisms, and they in turn feed on various sources. A food web shows the branching relationships and complex flow of energy in an ecosystem.

Key points about energy flow:

• Energy flow is **unidirectional**. Energy captured by autotrophs flows to consumers and decomposers; it does not revert back to earlier levels or the Sun.
• Energy available at each trophic level **diminishes progressively** due to energy loss at each transfer.

Introduction of non-degradable harmful chemicals into the environment, such as pesticides used in agriculture, can enter the food chain. Plants absorb these chemicals from the soil or water. These chemicals then pass to herbivores, then to carnivores. Since these chemicals are not broken down by biological processes, they accumulate in the tissues of organisms. The concentration of these chemicals increases progressively at each trophic level. This phenomenon is called **biological magnification** (or biomagnification). As humans often occupy the top trophic levels in food chains, the maximum concentration of these harmful chemicals can accumulate in our bodies, posing health risks. Pesticide residues can be found in grains, vegetables, fruits, meat, etc., and are difficult to remove.

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How Do Our Activities Affect The Environment?

Humans are part of the environment, and our increasing population and activities have a significant impact on ecological balance. We have learned how activities like pollution (air, water, soil) affect the environment. Two major environmental problems caused by human activities are the depletion of the ozone layer and the challenge of waste disposal.

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Ozone Layer And How It Is Getting Depleted

**Ozone (O$_3$)** is a molecule consisting of three oxygen atoms. While it is a deadly poison at ground level, the ozone layer in the higher levels of the atmosphere (stratosphere) performs a critical function: it shields the Earth's surface from harmful **ultraviolet (UV) radiation** from the Sun. UV radiation is damaging to organisms, causing skin cancer, eye damage, and harm to plants and aquatic life.

Ozone in the stratosphere is formed naturally by the action of UV radiation on oxygen molecules (O$_2$). Higher energy UV radiation splits some O$_2$ molecules into free oxygen atoms (O). These free atoms then combine with other O$_2$ molecules to form ozone (O$_3$).

O$_2$ $\xrightarrow{\text{UV}}$ O + O

O + O$_2$ $\to$ O$_3$

The amount of ozone in the atmosphere began to decrease sharply in the 1980s, forming an 'ozone hole' (a significant thinning of the layer, particularly over Antarctica). This depletion is caused by human-made synthetic chemicals, primarily **chlorofluorocarbons (CFCs)**. CFCs are used as refrigerants, propellants in aerosol sprays, and in fire extinguishers. In the upper atmosphere, UV radiation breaks down CFCs, releasing chlorine atoms. These chlorine atoms act as catalysts, repeatedly breaking down ozone molecules, leading to ozone depletion.

Recognizing the severity of the problem, the United Nations Environment Programme (UNEP) facilitated an international agreement in 1987 (the Montreal Protocol) to freeze CFC production at 1986 levels. Subsequently, agreements have mandated the phase-out of CFCs and the development of CFC-free alternatives worldwide. These regulations have shown some success in slowing down ozone depletion and have led to observations of the ozone layer gradually beginning to recover over time.

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Managing The Garbage We Produce

Our modern lifestyles generate enormous amounts of waste materials, often called garbage. The way we manage and dispose of this garbage has significant environmental consequences.

Waste materials can be classified based on whether they can be broken down by biological processes:

• **Biodegradable substances:** Materials that can be decomposed (broken down into simpler, harmless substances) by the action of microorganisms (bacteria, fungi). Examples: kitchen waste (food scraps, vegetable peels), paper, cotton cloth, wood.
• **Non-biodegradable substances:** Materials that cannot be broken down by biological processes. They persist in the environment for a very long time. Examples: plastics, metal objects, glass, certain chemicals (like pesticides, heavy metals).

Biodegradable waste, when managed properly (e.g., composting), can be beneficial, returning nutrients to the soil. However, if not managed well (e.g., large landfills of mixed waste), decomposition can occur anaerobically, producing harmful gases and unpleasant odours. Uncontrolled decomposition can also attract pests.

Non-biodegradable waste poses significant problems:

• They accumulate in the environment, polluting land, water, and air.
• They can harm wildlife (e.g., animals ingesting plastic, entanglement).
• Some non-biodegradable substances (like certain plastics or electronic waste components) can release toxic chemicals into the environment as they degrade slowly over time.
• Their persistence for hundreds or thousands of years makes their disposal a long-term challenge.

Increased consumption, changes in packaging (more disposable and plastic packaging), and lifestyle changes have led to a rise in the amount of non-biodegradable waste generated.

Effective waste management strategies are essential and include:

• **Source reduction:** Reducing the amount of waste generated in the first place.
• **Segregation:** Separating biodegradable and non-biodegradable waste at the source (homes, businesses) to facilitate different treatment methods.
• **Composting:** Decomposing biodegradable waste to create valuable compost (manure).
• **Recycling:** Processing non-biodegradable materials (plastics, glass, metals) to make new products, conserving resources and reducing landfill waste.
• **Safe Disposal:** Using environmentally sound methods for disposing of residual waste, such as sanitary landfills or incineration (with energy recovery and pollution control).
• **Managing Hazardous Waste:** Special handling and disposal methods for hazardous non-biodegradable waste (e.g., electronic waste, medical waste, industrial chemicals).

Individual actions like carrying cloth bags, switching off unnecessary lights, and walking instead of using vehicles also contribute to reducing resource consumption and environmental impact.

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Page No. 214

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Page No. 216

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