Our Environment
Ecosystems, food chains and the 10% law, ozone depletion and waste management.
Based on NCERT Class 10 Science, Chapter 13
13.1 Ecosystem and its components
- An ecosystem is made of all interacting organisms in an area (biotic) together with the non-living physical factors — temperature, rainfall, wind, soil, light (abiotic).
- Producers (green plants and blue-green algae) make food by photosynthesis; consumers (herbivores, carnivores, omnivores, parasites) eat other organisms.
- Decomposers such as bacteria and fungi break down dead remains and return nutrients to the soil, completing the cycle.
- Biodegradable substances are broken down by decomposers; non-biodegradable ones such as plastics and DDT persist and pollute.
Watch it happen — Biodegradable or Not?
Controls
Live result
Reduce, reuse and recycle — the three Rs keep non-biodegradable waste out of ecosystems.
13.1.1 Food chains and webs — the 10% law
- A food chain is a series of organisms with each level feeding on the previous one; each step is a trophic level.
- Only about 10% of the energy at a trophic level passes to the next level; the rest is lost mostly as heat. That is why food chains usually have only three or four steps.
- Energy flow is unidirectional — it never returns to the Sun — while nutrients cycle. Many interconnected chains form a food web.
Ten per cent law: energy passed on ≈ 10% of energy receivedWatch it happen — 10% Energy Flow Law
Controls
Live result
Only about 10% of energy moves to the next level, so food chains rarely exceed 4–5 levels.
Q1.Explain the 10% law with an example of a food chain of four trophic levels.
3 marksBiological magnification
- Harmful non-biodegradable chemicals such as pesticides enter the food chain from soil and water.
- They cannot be broken down or excreted, so their concentration increases at each higher trophic level — biological magnification.
- Human beings, being at the top of many food chains, receive the highest concentration.
Watch it happen — Biomagnification Tracker
Controls
Live result
Non-biodegradable chemicals accumulate at each level — humans at the top are most affected.
Q1.What is biological magnification? Why are humans at maximum risk?
2 marks13.2.1 Ozone layer and its depletion
- Ozone (O₃) high in the atmosphere absorbs harmful ultraviolet radiation from the Sun; UV causes skin cancer and cataract.
- It is formed when UV splits O₂ molecules into free oxygen atoms which then combine with O₂.
- Chlorofluorocarbons (CFCs) used in refrigerators and fire extinguishers destroy ozone. In 1987 UNEP agreed to freeze CFC production, and since 1987 all new refrigerators are meant to be CFC-free.
O₂ →(UV) O + O ; O + O₂ → O₃Watch it happen — Ozone Depletion Model
Controls
Live result
The 1987 Montreal Protocol froze CFC production, and the ozone layer is now slowly recovering.
Q1.How is ozone formed in the upper atmosphere and why is its depletion a matter of concern?
3 marks13.2.2 Managing the garbage we produce
- Improved lifestyle and packaging have hugely increased the waste we generate.
- Waste should be separated into biodegradable and non-biodegradable at source; biodegradable waste can be composted or turned into biogas.
- Methods of disposal include recycling, composting, sewage treatment, landfills and incineration — reduce, reuse and recycle come first.
Watch it happen — Biodegradable or Not?
Controls
Live result
Reduce, reuse and recycle — the three Rs keep non-biodegradable waste out of ecosystems.
Q1.Give two differences between biodegradable and non-biodegradable substances with one example each.
2 marks