Our Environment — Class 5 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 5 Science. Ecosystems, the pollution we cause, and what to do about our waste.
1. What an ecosystem is
An ecosystem is a community of living organisms interacting with their non-living surroundings.
Both halves matter. A pond is not just the fish in it; it is the fish, the plants, the insects and the microorganisms together with the water, the mud, the sunlight and the air dissolved in the water.
Biotic components are the living parts: plants, animals and microorganisms.
Abiotic components are the non-living parts: sunlight, water, soil, air and temperature.
| Ecosystem | Biotic | Abiotic |
|---|---|---|
| Pond | Fish, frogs, water plants, insects, algae | Water, mud, sunlight, dissolved air, temperature |
| Forest | Trees, deer, tigers, birds, fungi | Soil, rainfall, sunlight, air, temperature |
Change one abiotic part and the living things feel it at once. Drain the pond and every organism in it is affected.
2. Air pollution
Causes: smoke from vehicles and factories, burning of garbage and crop stubble, bursting firecrackers, and dust from construction.
Effects: asthma, bronchitis and lung diseases; acid rain, formed when sulphur dioxide and nitrogen dioxide dissolve in rainwater; and global warming.
3. Water pollution
Causes: untreated sewage from houses, chemicals and hot water released by factories, and fertilisers and pesticides washed off farms by rain.
Effects: cholera, typhoid and diarrhoea in people, and the death of fish and water plants.
4. Soil pollution
Causes: excess use of chemical fertilisers and pesticides, dumping of plastic and other non-biodegradable waste, and industrial waste.
Effects: the soil loses fertility, harmful chemicals enter crops and reach us through food, and earthworms and other useful soil life are killed.
5. The four Rs
You may know three Rs. There is a fourth that comes before them all.
Refuse — say no to what you do not need at all: a plastic straw, a single-use bag, extra packaging.
Reduce — use less of what you do need: carry a cloth bag, use both sides of the paper.
Reuse — use things again instead of discarding them: refill glass bottles, turn old clothes into dusters.
Recycle — send waste to be made into something new: paper, glass, metal and some plastics.
They are in order of how much good they do. Waste that is refused never exists, so it costs nothing to handle. Recycling is last because it is far better than dumping but still uses energy.
6. Segregating waste at source
Recycling only works if waste is separated where it is produced.
- Green bin — wet biodegradable waste: kitchen scraps, vegetable peels, garden leaves
- Blue bin — dry recyclable waste: paper, plastic, glass, metal
- Kept separate — hazardous waste: batteries, medicines, electronics
Mixing wet and dry waste ruins both. The wet waste soaks the paper and cardboard so they can no longer be recycled, and the dry waste contaminates what could otherwise have been composted. That single habit sends more recyclable material to landfill than anything else.
7. Two things never to do
Never burn dry leaves or garbage. Burning releases fine PM2.5 particles, carbon monoxide and toxic gases. Dry leaves should be composted instead — they are excellent for it.
Never burn plastic. It releases dioxins and furans, which cause cancer and lung disease.
8. Worked examples
Example 1. Define an ecosystem.
Solution: A community of living organisms interacting with their non-living surroundings.
Example 2. Name three biotic and three abiotic components of a pond.
Solution: Biotic: fish, water plants, insects. Abiotic: water, sunlight, mud.
Example 3. What causes acid rain?
Solution: Sulphur dioxide and nitrogen dioxide from vehicles and factories dissolving in rainwater.
Example 4. Name two diseases caused by water pollution.
Solution: Cholera and typhoid.
Example 5. How does excess fertiliser harm the soil?
Solution: It reduces the soil's fertility over time and kills earthworms and other useful soil life, and the chemicals enter our food through crops.
Example 6. Name the four Rs in order and explain the order.
Solution: Refuse, Reduce, Reuse, Recycle. They run from most to least effective: waste refused never exists, while recycling still consumes energy.
Example 7. Why should dry leaves be composted rather than burnt?
Solution: Burning them releases fine particles and toxic gases, while composting turns them into nutrient-rich material for the soil.
9. Practice
- What is an ecosystem?
- Give two examples each of biotic and abiotic components of a forest.
- Name four causes of air pollution.
- Name three sources of water pollution.
- Give two effects of soil pollution.
- Name the four Rs.
- Which bin does a vegetable peel go into, and which does a newspaper go into?
- Why must wet and dry waste not be mixed?
- Name two gases released by burning plastic.
10. Answers
- A community of living organisms interacting with their non-living environment.
- Biotic: trees and deer. Abiotic: soil and sunlight.
- Vehicle and factory smoke, burning garbage or stubble, firecrackers, and construction dust.
- Untreated sewage, industrial waste, and agricultural runoff of fertilisers and pesticides.
- The soil loses fertility, and harmful chemicals reach us through the crops grown in it.
- Refuse, Reduce, Reuse, Recycle.
- A vegetable peel goes into the green bin and a newspaper into the blue bin.
- Because wet waste soils the paper and cardboard so they cannot be recycled, and contaminates what could have been composted.
- Dioxins and furans.
11. Summary
- An ecosystem is living organisms interacting with their non-living surroundings.
- Biotic components are plants, animals and microorganisms; abiotic are sunlight, water, soil, air and temperature.
- Air pollution comes from vehicles, factories, open burning and firecrackers, and causes lung disease and acid rain.
- Water pollution comes from sewage, industrial waste and farm runoff, and spreads cholera and typhoid.
- Soil pollution from excess chemicals and plastic destroys fertility and enters our food.
- The four Rs are Refuse, Reduce, Reuse and Recycle, in order of effectiveness.
- Waste must be separated at source: green bin for wet, blue for dry, hazardous kept apart.
- Mixing wet and dry waste ruins both streams.
- Never burn leaves, garbage or plastic; compost the leaves instead.
