Our Environment

• The components of an ecosystem: biotic (living) and abiotic (non-living) factors
• Food chains, food webs, and trophic levels
• The 10% law of energy flow between trophic levels
• The role of decomposers in recycling nutrients
• The ozone layer, its depletion, and biological magnification
• Types of waste and sustainable waste management using the 3 Rs

1. Ecosystem components: An ecosystem consists of biotic components (all living organisms — producers, consumers, and decomposers) and abiotic components (non-living factors such as sunlight, temperature, water, air, and soil) that interact with each other. Producers (green plants, algae) make their own food via photosynthesis; consumers (herbivores, carnivores, omnivores) depend on other organisms for food; decomposers (bacteria, fungi) break down dead organic matter.

2. Food chains and food webs: A food chain is a sequence in which organisms feed on one another, showing a one-way flow of energy: Producer → Herbivore (primary consumer) → Carnivore (secondary consumer) → Top carnivore (tertiary consumer). In nature, food chains interconnect to form a food web, since most organisms eat and are eaten by more than one type of organism, making ecosystems more stable.

3. Trophic levels and the 10% law: Each step in a food chain is a trophic level. Producers occupy the first trophic level, herbivores the second, and so on. When energy is transferred from one trophic level to the next, only about 10% of the energy is passed on; roughly 90% is lost as heat during life processes (respiration, movement, growth) at each level. This is why food chains rarely have more than 4-5 trophic levels — there is too little energy left to support another level.

4. Decomposers: Bacteria and fungi break down dead plants, animals, and waste products into simpler inorganic substances that go back into the soil, water, and air, to be reused by producers. Decomposers are essential for recycling nutrients and preventing the accumulation of dead matter in the environment.

5. Ozone layer: The ozone (O₃) layer in the upper atmosphere (stratosphere) absorbs harmful ultraviolet (UV) radiation from the sun, protecting life on Earth from damage such as skin cancer and eye damage. Ozone depletion is caused mainly by chemicals like chlorofluorocarbons (CFCs), once widely used in refrigerators, air conditioners, and aerosol sprays, which break down ozone molecules in the stratosphere. International agreements (such as the Montreal Protocol) aim to reduce CFC use.

6. Biological magnification: Harmful, non-biodegradable chemicals (such as certain pesticides like DDT) that enter a food chain do not break down easily. As these chemicals pass from one trophic level to the next, their concentration increases at each successive level because organisms at higher trophic levels eat many organisms from the level below, accumulating the toxin in their bodies. This means top carnivores (including humans) end up with the highest, most dangerous concentrations.

7. Waste management: Waste can be biodegradable (broken down by natural biological processes, e.g. food scraps, paper, cotton) or non-biodegradable (not easily broken down, e.g. plastics, glass, metals — some can persist in the environment for hundreds of years). Managing waste sustainably relies on the 3 Rs: Reduce (use less, avoid waste generation), Reuse (use items again instead of discarding), and Recycle (process waste materials to make new products), which together reduce the environmental burden of waste, especially non-biodegradable waste.

Problem: Suppose a grassland food chain is: Grass → Grasshopper → Frog → Snake → Eagle. If the grass produces 100,000 joules (J) of energy through photosynthesis, calculate the energy available to the eagle (the top carnivore) using the 10% law. How many trophic levels are between grass and the eagle?

Solution: Using the 10% law, only 10% of energy is transferred to the next trophic level:

• Grass (producer): 100,000 J
• Grasshopper (primary consumer): 10% of 100,000 = 10,000 J
• Frog (secondary consumer): 10% of 10,000 = 1,000 J
• Snake (tertiary consumer): 10% of 1,000 = 100 J
• Eagle (quaternary consumer): 10% of 100 = 10 J

There are 4 energy transfers (4 trophic level jumps) between the grass and the eagle. This sharp drop in available energy explains why food chains are typically short — very little usable energy remains to support additional trophic levels beyond 4-5 steps.

Grass (100,000 J) --10%--> Grasshopper (10,000 J) --10%--> Frog (1,000 J)
      --10%--> Snake (100 J) --10%--> Eagle (10 J)

• Thinking a food web is just "many food chains drawn separately" — a food web specifically shows the interconnections where organisms have multiple feeding relationships, making the ecosystem more resilient than a single linear food chain.
• Believing decomposers only "clean up" the environment — they are essential for recycling nutrients (like carbon and nitrogen) back to producers, without which ecosystems could not sustain new plant growth.
• Confusing ozone depletion with global warming — although both are environmental problems, ozone depletion specifically refers to the thinning of the stratospheric ozone layer (mainly by CFCs) that reduces UV protection, while global warming is caused by greenhouse gases trapping heat.
• Assuming biological magnification affects only the species that first absorbs the toxin — in fact, concentration increases at each higher trophic level, so top carnivores (often including humans, who eat fish, meat, etc.) are affected the most.

• If 1,00,000 J of energy is available at the producer level, how much energy is available at the third trophic level (using the 10% law)?
• Name two biodegradable and two non-biodegradable waste materials, and explain which of the 3 Rs would best reduce the environmental impact of the non-biodegradable ones.

Open the Practice tab for graded questions on Our Environment.