Our Environment

13.1 ECO-SYSTEM — WHAT ARE ITS COMPONENTS?

An ecosystem is a complex system where living organisms (biotic components) and non-living factors (abiotic components) interact with each other.

Biotic components include plants, animals, microorganisms, and humans, while abiotic components include temperature, rainfall, wind, soil, and minerals.

Examples of ecosystems include gardens, forests, ponds, lakes, and crop fields.

Producers are organisms, such as green plants and certain bacteria, that can use radiant energy from the sun and chlorophyll to convert inorganic substances into organic compounds like sugar and starch through photosynthesis.

Consumers are organisms that depend on producers either directly or indirectly for their sustenance.

Herbivores are consumers that eat plants (e.g., cows, rabbits).

Carnivores are consumers that eat other animals (e.g., lions, wolves).

Omnivores are consumers that eat both plants and animals (e.g., humans, bears).

Parasites are consumers that live in or on another organism and obtain nutrients from it (e.g., fleas, ticks).

Decomposers, such as bacteria and fungi, break down the dead remains and waste products of organisms. They convert complex organic substances into simple inorganic substances, which are used by plants and returned to the soil.

If decomposers are absent, the natural replenishment of the soil would be hindered, and the accumulation of garbage, dead animals, and plants would persist without being broken down into simpler substances.

13.1.1 Food Chains and Webs

A food chain is a series of organisms in an ecosystem that feed on one another, forming trophic levels.

Autotrophs (producers) are at the first trophic level, converting solar energy into chemical energy through photosynthesis.

Herbivores (primary consumers) occupy the second trophic level, followed by small carnivores (secondary consumers) at the third trophic level, and larger carnivores (tertiary consumers) at the fourth trophic level.

Energy flows from one trophic level to another, but there is a loss of energy at each step.

Approximately 1% of solar energy is captured by green plants, and about 10% of the food energy is transferred to the next trophic level.

Food chains generally consist of three or four trophic levels due to the significant loss of energy.

Producers (autotrophs) outnumber other organisms in an ecosystem.

Food chains can be interconnected and form a complex network called a food web.

Energy flow in a food chain is unidirectional and diminishes at each trophic level.

Harmful chemicals, such as pesticides, can enter the food chain through soil or water pollution and accumulate in organisms at higher trophic levels.

Human beings, occupying the top level of food chains, can accumulate the highest concentration of these chemicals, a phenomenon known as biological magnification.

13.2 HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT?

13.2.1 Ozone Layer and How it is Getting Depleted

Ozone (O3) is a molecule composed of three oxygen atoms and is formed by the action of UV radiation on oxygen (O2) molecules in the higher levels of the atmosphere.

Ozone acts as a shield, protecting the Earth's surface from harmful ultraviolet (UV) radiation from the Sun, which can cause damage to organisms, including skin cancer in humans.

While ozone is a deadly poison at lower levels, it performs an essential function in the upper atmosphere.

The process of ozone formation involves UV radiation splitting apart oxygen molecules, resulting in free oxygen atoms that combine with other oxygen molecules to form ozone.

The depletion of ozone in the atmosphere started to occur significantly in the 1980s.

Synthetic chemicals called chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers, have been linked to the depletion of ozone.

In 1987, the United Nations Environment Programme (UNEP) established an agreement to freeze CFC production at 1986 levels.

It is now mandatory for manufacturing companies worldwide to produce CFC-free refrigerators.

These efforts aim to reduce the depletion of ozone in the atmosphere and protect the Earth from harmful UV radiation.

13.2.2 Managing the Garbage We Produce

In our daily activities, we generate various waste materials, some of which include:

Food waste

Packaging materials (plastic wrappers, cardboard boxes, etc.)

Disposable items (cups, plates, utensils)

Paper waste

Electronic waste (old devices, batteries)

Chemical waste (cleaning agents, pesticides, etc.)

After we throw away these waste materials:

Biodegradable substances can be broken down by biological processes, such as the action of bacteria or other saprophytes.

Non-biodegradable substances, such as plastics, do not break down easily through biological processes. They may persist in the environment for a long time or harm the ecosystem.

Non-biodegradable materials can undergo physical processes like heat and pressure, but they still persist in the environment under ambient conditions.

Many towns and cities face the problem of garbage accumulation, with heaps of garbage found in various places.

Changes in lifestyle and attitudes, including the use of disposable items and non-biodegradable packaging, have led to increased waste generation.

Non-biodegradable waste materials can have a significant impact on the environment, such as pollution, littering, and harm to ecosystems.

Proper waste management practices, recycling, and reducing the use of non-biodegradable materials are essential to mitigate the environmental impact of waste.

INTEXT QUESTIONS

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1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Ans: Trophic levels are hierarchical levels in a food chain or food web, representing the different positions occupied by organisms based on their feeding relationships and energy transfer. Each trophic level represents a different group of organisms that obtain their energy in a similar way.

Example of a food chain:

Grass -> Grasshopper -> Frog -> Snake -> Hawk

In this food chain, the trophic levels are:

Trophic Level 1: Grass (producer)

Trophic Level 2: Grasshopper (primary consumer)

Trophic Level 3: Frog (secondary consumer)

Trophic Level 4: Snake (tertiary consumer)

Trophic Level 5: Hawk (quaternary consumer)

2. What is the role of decomposers in the ecosystem?

Ans: Decomposers play a crucial role in the ecosystem by breaking down dead organic matter and waste materials, returning nutrients back into the environment. Their main functions include:

Decomposition: Decomposers, such as bacteria and fungi, break down complex organic substances (such as dead plants, animals, and waste) into simpler inorganic substances.

Nutrient Recycling: By decomposing organic matter, decomposers release nutrients, such as carbon, nitrogen, and phosphorus, back into the soil or water. These nutrients can then be used by producers (plants) for growth and development.

Detoxification: Decomposers also help in the breakdown and detoxification of harmful substances and pollutants present in organic matter, reducing their potential harm to the environment.

Maintaining Ecosystem Balance: Decomposers play a crucial role in maintaining the balance of nutrients and energy flow within ecosystems. They ensure the continuous cycling of materials and the availability of essential elements for other organisms.

Overall, decomposers help in the efficient recycling of nutrients, energy flow, and the decomposition of organic matter, contributing to the overall health and functioning of the ecosystem.

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1. Why are some substances biodegradable and some non-biodegradable?

Ans: The biodegradability of substances depends on their chemical composition and their ability to be broken down by biological processes. Biodegradable substances have chemical structures that can be easily broken down by enzymes produced by bacteria, fungi, and other microorganisms. These enzymes can recognize and digest the specific bonds in biodegradable substances, converting them into simpler compounds. On the other hand, non-biodegradable substances have chemical structures that are resistant to enzymatic degradation, making it difficult for microorganisms to break them down naturally.

2. Give any two ways in which biodegradable substances would affect the environment.

Ans: Ways in which biodegradable substances can affect the environment:

Nutrient Recycling: Biodegradable substances, when decomposed, release nutrients back into the environment. These nutrients can be used by plants for growth, supporting the overall productivity and health of ecosystems.

Soil Enrichment: Biodegradable substances, such as organic matter, can improve soil fertility and structure, enhancing water retention and nutrient availability for plant growth.

3. Give any two ways in which non-biodegradable substances would affect the environment.

Ans: Ways in which non-biodegradable substances can affect the environment:

Pollution: Non-biodegradable substances, such as plastics and synthetic chemicals, can accumulate in the environment, leading to pollution of land, water bodies, and the atmosphere. This pollution can harm and disrupt ecosystems, impacting the health and survival of organisms.

Wildlife and Marine Life Impact: Non-biodegradable substances, especially plastics, can be ingested by animals, causing blockages in their digestive systems, injuries, or even death. Marine life, in particular, is vulnerable to plastic pollution, with animals like turtles, birds, and marine mammals being entangled or ingesting plastic debris.

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1. What is ozone and how does it affect any ecosystem?

ANS: Ozone (O3) is a molecule composed of three oxygen atoms. It plays a crucial role in the Earth's atmosphere, existing in two different regions: the troposphere and the stratosphere. In the troposphere, which is the lower part of the atmosphere, ozone is considered a pollutant and a component of smog. It is harmful to living organisms, including humans, as it can cause respiratory issues and damage plant tissues.

In the stratosphere, ozone forms a protective layer known as the ozone layer. This layer is vital as it absorbs a significant portion of the Sun's ultraviolet (UV) radiation, preventing it from reaching the Earth's surface. UV radiation is known to be harmful to living organisms, causing skin cancer, cataracts, and other health problems. Therefore, the ozone layer plays a crucial role in protecting ecosystems by shielding them from excessive UV radiation

2. How can you help in reducing the problem of waste disposal? Give any two methods.

ANS: Reduce, Reuse, Recycle: One of the most effective ways to reduce waste is to practice the three Rs - Reduce, Reuse, and Recycle. By reducing the amount of waste generated, reusing items instead of disposing of them, and recycling materials whenever possible, the overall volume of waste sent to landfills or incinerators can be significantly reduced.

Composting: Composting is the process of turning organic waste, such as food scraps, yard trimmings, and certain paper products, into nutrient-rich compost. By composting organic waste, it can be diverted from landfills and utilized as a natural fertilizer for plants and gardens. Composting not only reduces waste but also contributes to soil health and reduces the need for chemical fertilizers.

Responsible Disposal: Properly disposing of hazardous waste, such as batteries, electronic devices, and chemicals, is essential to prevent environmental contamination. Many communities have designated drop-off points or recycling centers for hazardous materials. Ensuring that these materials are disposed of correctly can help minimize their negative impact on the environment.

Educate and Spread Awareness: By educating others about the importance of waste reduction and proper waste disposal practices, you can help raise awareness and encourage more sustainable behaviors. Sharing information about recycling programs, composting techniques, and the environmental impacts of waste can inspire others to take action and make conscious choices in their daily lives.

EXERCISES

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

ANS: The group that contains only biodegradable items is (c) Fruit-peels, cake, and lime-juice. Biodegradable items are those that can be broken down and decomposed by natural processes, such as the actions of microorganisms, into simpler substances and recycled in the environment.

2. Which of the following constitutes a food chain?

(a) Grass, wheat, and mango

(b) Grass, goat, and human

(c) Goat, cow, and elephant

(d) Grass, fish, and goat

ANS: The food chain among the given options is (b) Grass, goat, and human. A food chain represents the transfer of energy and nutrients from one organism to another in a linear sequence. In this case, grass is consumed by a goat, and the goat is consumed by a human, forming a simple food chain.

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 

ANS: All of the above options (a) Carrying cloth bags while shopping, (b) Switching off unnecessary lights and fans, and (c) Walking to school instead of using a vehicle are environment-friendly practices. These actions contribute to reducing the use of plastic bags, conserving energy, and minimizing carbon emissions, respectively, leading to a positive impact on the environment.

4. What will happen if we kill all the organisms at one trophic level?

ANS:  If all the organisms in one trophic level are killed, it would disrupt the flow of energy and nutrients in the ecosystem. Organisms in each trophic level depend on the organisms in the lower trophic levels for their food source. If a trophic level is completely eliminated, it would lead to a cascading effect throughout the food chain, affecting the higher trophic levels as well.

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?

ANS: The impact of removing all the organisms in a trophic level can vary depending on the specific ecosystem and the trophic level in question. However, in general, the removal of organisms from any trophic level would have consequences for the rest of the ecosystem. Each trophic level plays a role in maintaining the balance and functioning of the ecosystem, and the removal of any trophic level can disrupt the overall dynamics.

6. What is biological magnification? Will the levels of this magnification be different at

different levels of the ecosystem?

ANS: Biological magnification refers to the process where certain harmful substances, such as pesticides or heavy metals, become more concentrated in organisms as they move up the food chain. This occurs because the concentration of these substances increases as they are accumulated and transferred from one organism to another. The levels of biological magnification can vary at different levels of the ecosystem, with higher trophic levels often experiencing higher levels of magnification due to the cumulative effect of consuming organisms lower in the food chain.

7. What are the problems caused by the non-biodegradable wastes that we generate?

ANS: Non-biodegradable wastes pose several problems in the environment. They do not break down easily through natural processes and can persist in the environment for long periods. These wastes can accumulate in landfills, pollute water bodies, harm wildlife, and cause environmental degradation. Plastics, for example, take hundreds of years to decompose and contribute to the pollution of oceans and land.

8. If all the waste we generate is biodegradable, will this have no impact on the

environment?

ANS: Even if all the waste generated is biodegradable, it can still have an impact on the environment. While biodegradable waste can be broken down by natural processes, its improper disposal or excessive generation can lead to issues such as the release of greenhouse gases during decomposition, contamination of soil and water bodies if not managed properly, and depletion of resources required for decomposition, such as oxygen in water bodies.

9. Why is damage to the ozone layer a cause for concern? What steps are being taken

to limit this damage?

ANS: Even if all the waste generated is biodegradable, it can still have an impact on the environment. While biodegradable waste can be broken down by natural processes, its improper disposal or excessive generation can lead to issues such as the release of greenhouse gases during decomposition, contamination of soil and water bodies if not managed properly, and depletion of resources required for decomposition, such as oxygen in water bodies.

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