An ecosystem consists of all the interacting organisms in an area together with the non-living constituents of the environment.

Examples include forests, ponds, lakes, gardens and crop-fields.

Producers are organisms that can produce food from inorganic substances using radiant energy from the Sun in the presence of chlorophyll.

Examples: Green plants and certain bacteria that carry out photosynthesis.

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

• Herbivores
• Carnivores
• Omnivores
• Parasites

Decomposers are microorganisms such as bacteria and fungi that break down dead remains and waste products of organisms.

They convert complex organic substances into simple inorganic substances which go into the soil and can be used again by plants.

An aquarium is designed and maintained by humans. It contains living organisms such as aquatic plants and animals along with necessary abiotic components such as water, oxygen and food.

A food chain is a series of organisms in which organisms at different biotic levels feed on one another.

Each step or level of a food chain is called a trophic level.

1. First trophic level: Producers
2. Second trophic level: Primary consumers / herbivores
3. Third trophic level: Secondary consumers
4. Fourth trophic level: Tertiary consumers

1. Grass – Producer / First trophic level
2. Grasshopper – Primary consumer / Second trophic level
3. Frog – Secondary consumer / Third trophic level
4. Snake – Higher consumer
5. Eagle – Top consumer

A food web is a network of interconnected food chains.

An organism may be eaten by more than one type of organism and may itself feed on different organisms. Therefore, relationships are represented by branching food chains.

A large amount of energy is lost at each trophic level. Therefore, very little usable energy remains after four trophic levels, limiting the length of food chains.

Producers capture solar energy and convert it into chemical energy. This energy passes from producers to consumers and decomposers through food relationships.

Energy flows from the Sun to producers and then progressively through different trophic levels. Energy that passes to a higher trophic level does not return to the previous level.

On average, about 10% of the food eaten is converted into the organism's body and becomes available to the next trophic level.

A large amount of energy is lost to the environment as heat and is also used in processes such as digestion, movement and other life activities. Hence, progressively less energy is available at higher trophic levels.

Producers form the first trophic level and provide food and energy to the rest of the ecosystem. Because energy decreases at successive trophic levels, larger numbers of organisms are generally found at lower trophic levels.

Biological magnification is the phenomenon in which harmful, non-degradable chemicals accumulate progressively at each trophic level of a food chain.

Since human beings may occupy the top level of a food chain, the maximum concentration of such chemicals can accumulate in their bodies.

Certain harmful chemicals such as pesticides are not degraded easily. They enter soil or water, are absorbed by plants or aquatic organisms and then pass through successive trophic levels. Their concentration increases at higher trophic levels.

Harmful non-degradable chemicals accumulate progressively as they move through the food chain. Organisms at higher trophic levels consume organisms from lower levels and therefore accumulate greater concentrations.

Ozone (O₃) is a molecule formed by three atoms of oxygen.

At higher levels of the atmosphere, ozone performs an essential function by shielding the Earth's surface from harmful ultraviolet (UV) radiation from the Sun.

The ozone layer absorbs harmful ultraviolet radiation from the Sun and protects organisms on Earth from its damaging effects.

Excessive UV radiation can be highly damaging to organisms and is known to cause skin cancer in human beings.

High-energy UV radiation splits some oxygen molecules (O₂) into free oxygen atoms. These oxygen atoms then combine with molecular oxygen to form ozone (O₃).

The decrease in atmospheric ozone has been linked to synthetic chemicals such as chlorofluorocarbons (CFCs).

The NCERT chapter mentions their use in refrigerants and fire extinguishers.

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

The chapter also states that manufacturing companies were required to make CFC-free refrigerators throughout the world.

Substances that can be broken down by biological processes are called biodegradable substances.

Substances that cannot be broken down by biological processes are called non-biodegradable substances.

Such substances may persist in the environment for a long time and may harm different members of the ecosystem.

Examples include grass, flowers, wood, fruit peels and food materials such as cake.

Plastic is an important example of a material that is not broken down by biological processes and can persist in the environment for a long time.

• They may persist in the environment for a long time.
• They may accumulate in the surroundings.
• They may harm different members of an ecosystem.
• They contribute to serious waste-disposal problems.

No. Even biodegradable waste can create environmental problems if it is generated in large quantities or is not managed properly. Waste disposal remains an important environmental issue.

Removing all organisms from one trophic level would disturb the balance of the ecosystem and affect the organisms at other trophic levels because the organisms in an ecosystem are interdependent.

Yes. Different trophic levels have different roles in the ecosystem. Removing producers, for example, would directly affect the availability of food and energy for consumers. Removing consumers would also disturb the food relationships between organisms.

Biological magnification is the progressive accumulation of harmful non-degradable chemicals at successive trophic levels.

Yes. The concentration generally increases as we move toward higher trophic levels, with organisms at the top potentially having the maximum concentration.

Non-biodegradable wastes persist for long periods and may harm members of the ecosystem. Their accumulation creates serious environmental and waste-disposal problems.

The ozone layer protects the Earth's surface from harmful ultraviolet radiation. Damage to this layer allows more harmful UV radiation to reach the Earth's surface.

The use of ozone-depleting substances such as CFCs has been controlled. The chapter mentions international action through UNEP and measures to promote CFC-free refrigerators.