Our Environment — Class 3 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 3 Science. Living and non-living surroundings, and the balance between them.
1. Everything around us
The environment is everything that surrounds us. It has two kinds of parts.
Biotic parts are living: plants, animals, birds, insects, fish, humans, and the tiny organisms too small to see. Living things grow, need food, produce young and eventually die.
Abiotic parts are non-living: air, water, soil, sunlight, temperature and rocks.
| Biotic | Abiotic |
|---|---|
| Trees, grass, crops | Air, water, soil |
| Cows, birds, fish, insects | Sunlight, temperature |
| Humans | Rocks and stones |
2. Two things worth getting right
Soil is abiotic. It is made of ground-up rock, minerals and dead plant matter. Living things certainly live inside it, but the soil itself is not alive.
The Sun is abiotic. It gives the energy that every living thing depends on, but it does not grow, feed or reproduce, so it is not living.
A dead tree, on the other hand, is counted as biotic. It was once alive, and it is made of the material of a living thing.
3. Living and non-living depend on each other
Neither group manages alone.
- A plant is biotic, but it needs sunlight, water and soil, all abiotic, in order to grow.
- An animal is biotic, but it breathes oxygen from the air and drinks water, both abiotic.
- Fungi and bacteria break dead plants and animals back down into the soil, returning what was borrowed.
4. Ecosystems
An ecosystem is all the living and non-living parts of one area, working together.
A pond ecosystem has water, mud and sunlight on the non-living side, and fish, frogs, water plants and insects on the living side.
A forest ecosystem has soil, rainfall and sunlight together with trees, deer, tigers, birds and insects.
5. Balance, and what upsets it
An ecosystem is balanced when each part gets what it needs and no part grows out of control.
That balance is upset by:
- Cutting trees, which removes homes and food for many animals at once
- Pollution of air, water and soil
- Over-hunting or over-fishing, which removes one animal and leaves the ones it used to eat unchecked
Because every part is connected to the others, damage in one place travels. Cut the trees on a riverbank and the soil washes into the river, and the fish suffer next.
6. Worked examples
Example 1. Sort these into biotic and abiotic: crow, stone, mango tree, sunlight, well water.
Biotic: crow and mango tree. Abiotic: stone, sunlight and well water.
Example 2. A classmate says soil is biotic because worms live in it. Is this right?
No. The worms are biotic, but the soil itself is ground rock, minerals and dead matter, and it is abiotic.
Example 3. Name the biotic and abiotic parts of a pond.
Biotic: fish, frogs, water plants, insects. Abiotic: water, mud, sunlight.
Example 4. How does cutting trees on a riverbank affect the fish?
Tree roots hold the soil in place. Without them, soil washes into the river, muddying the water and harming the fish that live in it.
7. Practice
- Define the environment.
- Give three examples of biotic factors and three of abiotic factors.
- Is the Sun biotic or abiotic? Give a reason.
- Is a dead tree biotic or abiotic?
- What is an ecosystem?
- Name the living and non-living parts of a forest.
- Give two things that upset the balance of an ecosystem.
8. Answers
- Everything that surrounds us, both living and non-living.
- Biotic: plants, animals, humans. Abiotic: air, water, sunlight.
- Abiotic, because it does not grow, feed or reproduce, even though it supports life.
- Biotic, because it was once alive and is made of living material.
- All the living and non-living parts of an area, interacting together.
- Living: trees, deer, birds, insects. Non-living: soil, rainfall, sunlight.
- Cutting trees and polluting; over-hunting is another.
9. Summary
- The environment is everything around us, made of biotic and abiotic parts.
- Biotic means living; abiotic means non-living.
- Soil and the Sun are abiotic; a dead tree is still counted as biotic.
- Living things depend on non-living ones for sunlight, water, air and soil.
- An ecosystem is all the parts of one area working together, such as a pond or a forest.
- Cutting trees, pollution and over-hunting upset the balance.
- Because the parts are connected, damage in one place spreads to others.
