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Tamil Nadu (TNBSE)Class 3 Science★ 5-6 marks in TN Class 3 Term 3 exams — classification of biotic/abiotic factors, ecosystem concepts, and short written answers

Our Environment

Samacheer Kalvi (TN State Board) Class 3 Science — Chapter 8, Our Environment. Biodiversity and conservation. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 10 min readeasy-to-medium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Define environment as everything that surrounds us, made of biotic and abiotic factors
2Define biotic factors as all living things (plants, animals, humans, microorganisms)
3Define abiotic factors as all non-living things (air, water, soil, sunlight, temperature, rocks)
4Give examples of interaction between biotic and abiotic factors: plants need sunlight (abiotic) + water (abiotic) to grow; animals breathe oxygen (abiotic) from the air
5Explain what an ecosystem is: a community of living things interacting with each other and their non-living environment
6Understand the concept of a balanced ecosystem and what disturbs it (pollution, cutting trees, over-hunting)

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Why this chapter matters

Class 3 introduces a fundamental scientific concept: the environment is made of biotic (living) and abiotic (non-living) factors that are constantly interacting. A child looking at a pond sees not just water and fish — they see an ecosystem where water (abiotic) supports plants (biotic) which feed fish (biotic), and fish waste fertilises plants. This systems thinking — understanding that nothing exists in isolation — is the foundation of ecology. The chapter also introduces the idea of a balanced ecosystem and what happens when it is disturbed (pollution, deforestation).

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Our Environment — Class 3 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 3 Science, Chapter 8. Biodiversity and conservation.

1. About this chapter

This chapter covers Our Environment as part of the Class 3 Samacheer Kalvi Science curriculum. It deals with biodiversity and conservation and builds conceptual understanding essential for the TN School Term Exam.

By the end of this chapter, students will be able to:

Define biodiversity
Explain why conservation of nature is important

2. Key concepts

Concept 1: Define biodiversity.
Concept 2: Explain why conservation of nature is important.

3. Important terms and formulas

Term / Formula	Description
Define biodiversity…	Define biodiversity
Explain why conservation of…	Explain why conservation of nature is important

4. Worked examples

Example 1. Applying a key concept from this chapter.

Solution: Identify the relevant principle → apply the formula or rule → state the answer with correct units.

Example 2. A typical exam-style question on our environment.

Solution: Break the problem into steps, use the appropriate formula and verify the answer.

5. Common mistakes

Mistake: Skipping units or forgetting to state them. Fix: Always write units alongside every quantity and answer.
Mistake: Confusing similar terms or concepts in this chapter. Fix: Make a comparison table of the terms during revision.

6. Practice (exam-style)

Define the main term or principle covered in Chapter 8.
Give two real-life examples related to our environment.
Solve a short numerical or descriptive question from this chapter.
State one important formula and explain each symbol.

7. Answer key (hints)

Refer to section 2 (Key concepts) above for the definition.
Examples should be drawn from daily experience and local context.
Apply the formula from section 3, show all steps clearly.
Formula with units — refer to the textbook glossary for symbol meanings.

8. Quick revision

Class 3 Science — Chapter 8: Our Environment.
Core idea: Biodiversity and conservation.
Key outcomes: Define biodiversity; Explain why conservation of nature is important.
Always revise diagrams / tables from the Samacheer Kalvi textbook before the exam.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Biotic and Abiotic factors

Biotic (living) → plants, animals, birds, insects, fish, humans, fungi, bacteria. They grow, reproduce, need food, and eventually die. Abiotic (non-living) → air, water, soil, sunlight, temperature, rocks, minerals, wind. They do not grow, reproduce, or need food.

Biotic comes from the Greek word 'bios' meaning life. Abiotic = 'a' (without) + 'bios' (life) = without life. The two are inseparable — no biotic factor can survive without abiotic factors.

Interaction between biotic and abiotic factors

Plants (biotic) need sunlight (abiotic), water (abiotic), and soil (abiotic) to grow. Animals (biotic) breathe oxygen (abiotic) from the air and drink water (abiotic). Decomposers like fungi and bacteria (biotic) break down dead plants and animals, returning nutrients to the soil (abiotic).

This is nature's recycling system. Nothing is wasted. A dead leaf falls, decomposers break it down, and the nutrients return to the soil to feed the next generation of plants.

Ecosystem and balance

An ecosystem = all the biotic and abiotic factors in an area interacting together. A pond ecosystem: water (abiotic) + fish, frogs, water plants, insects (biotic). A forest ecosystem: soil, sunlight, rain (abiotic) + trees, deer, tiger, birds, insects (biotic). A balanced ecosystem has all components in the right proportions.

If you remove one component, the whole system is affected. If all frogs in a pond die, the insect population explodes, plants are overeaten, and the pond ecosystem collapses. Every link in the chain matters.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Thinking soil is biotic because it 'has life in it'

✓ Soil itself is abiotic — it is made of rock particles, minerals, and dead organic matter. The bacteria, earthworms, and insects LIVING in the soil are biotic. The soil (substance) is abiotic; the organisms in it are biotic.

WATCH OUT

✗ Calling the Sun 'biotic' because it supports life

✓ The Sun is abiotic — it is not alive. It does not grow, reproduce, or need food. It provides energy (sunlight) which is an abiotic factor essential for life. Supporting life does not make something living.

WATCH OUT

✗ Thinking a dead tree is abiotic

✓ A dead tree was once living and is now dead organic matter. It is still considered biotic because it came from a living organism. More importantly, dead wood supports a whole community of biotic decomposers (fungi, termites, bacteria).

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