13. Our Environment

The various steps in a food chain at which transfer of food (energy) takes place are called trophic levels.

Example: Grass → Grasshopper → Frog → Snake → Eagle

• First trophic level (producer): Grass
• Second trophic level (primary consumer / herbivore): Grasshopper
• Third trophic level (secondary consumer): Frog
• Fourth trophic level (tertiary consumer): Snake
• Fifth trophic level: Eagle

• Decomposers like bacteria and fungi break down dead plants, animals and their wastes.
• They change complex organic substances into simple inorganic substances.
• These simple substances go back into the soil and are used again by plants.
• They also clean the environment by removing dead bodies and wastes.

Substances that can be broken down by bacteria and other decomposers are biodegradable. For example, vegetable peels and paper.

Some substances like plastics cannot be broken down by these micro-organisms. Decomposers do not have enzymes to act on them. So they are non-biodegradable.

• Large amounts of rotting waste give a bad smell and spoil the surroundings.
• They attract flies and other insects that spread diseases.

• They remain in the environment for a long time and pollute soil and water.
• They may enter food chains and harm living organisms. Animals may also eat plastic bags and die.

Ozone (O₃) is a molecule made of three atoms of oxygen. It forms a layer in the upper atmosphere.

The ozone layer protects the earth from harmful ultraviolet (UV) radiation of the Sun. UV radiation can cause skin cancer in human beings and harm plants and animals. So the ozone layer is important for the safety of all ecosystems.

• Separate biodegradable and non-biodegradable wastes at home. Make compost from biodegradable waste.
• Follow the 3 Rs – reduce, reuse and recycle. For example, use cloth bags instead of plastic bags.

Answer: (a), (c) and (d)

Plastic in group (b) is non-biodegradable. All other items are biodegradable.

Answer: (b) Grass, goat and human

Answer: (d) All of the above

The food chain will break. The organisms of the next trophic level will not get food and will die out. The organisms of the previous trophic level will increase in number, as nothing eats them. So the balance of the ecosystem will be disturbed.

Yes, the impact will be different.

• If producers are removed, no energy will enter the ecosystem. All other organisms will die.
• If herbivores are removed, producers will grow without control. Carnivores will starve.
• If carnivores are removed, herbivores will increase too much and eat up the plants.

No, the organisms of any trophic level cannot be removed without damaging the ecosystem. All trophic levels depend on each other.

Harmful chemicals like pesticides enter the food chain. They are not broken down. So they collect in the bodies of organisms. Their concentration increases at each higher trophic level. This is called biological magnification.

Yes, the levels will be different. The concentration is lowest in producers and highest at the top trophic level. Human beings are at the top of many food chains, so they collect the largest amount.

• They stay in the environment for a long time and pollute soil, water and air.
• They block drains and sewers, which causes water-logging.
• Animals that eat plastic may get choked and die.
• Harmful chemicals from them can enter food chains and cause biological magnification.

No, it will still have an impact. Large amounts of biodegradable waste take time to break down. Rotting waste gives a bad smell and attracts flies and germs that spread diseases. It may also release gases like methane. So even biodegradable waste must be managed properly, for example by composting.

The ozone layer protects the earth from harmful UV radiation of the Sun. If it is damaged, more UV radiation will reach the earth. This can cause skin cancer and eye damage in human beings. It can also harm plants and animals.

Steps taken: The amount of ozone fell sharply in the 1980s because of chlorofluorocarbons (CFCs). In 1987, the United Nations Environment Programme (UNEP) made an agreement to freeze CFC production at 1986 levels. Now CFC-free refrigerators are made, and countries are working to stop the use of CFCs.