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Tamil Nadu (TNBSE)Class 4 Science★ 6-8 marks in TN Class 4 Term 1 exams — tooth types, digestive and respiratory system functions, sense organs, and labelled diagrams

My Body

Samacheer Kalvi (TN State Board) Class 4 Science — Chapter 1, My Body. Internal organs, teeth and dental care. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 12 min readMedium difficulty✓ Free · NCERT-aligned

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

1Name the 4 types of teeth and their functions: incisors (cutting), canines (tearing), premolars (crushing), molars (grinding)
2State that an adult has 32 permanent teeth (including 4 wisdom teeth), while a child has 20 milk teeth
3Describe the difference between milk teeth (temporary, 20, start falling at age 6-7) and permanent teeth (32, last a lifetime)
4List 3 ways to care for teeth: brush twice daily with fluoride toothpaste, rinse mouth after every meal, avoid too many sweets and sticky foods, visit a dentist every 6 months
5Trace the path of food through the digestive system: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus
6Trace the path of air: nose → windpipe/trachea → lungs (bronchi → bronchioles → alveoli)
7List the 5 sense organs and their functions with the specific part of each organ that detects stimuli

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Why this chapter matters

Class 4 My Body introduces a topic every child experiences but few understand: teeth. Children learn the four types of teeth (incisors for cutting, canines for tearing, premolars and molars for grinding), the difference between milk teeth and permanent teeth, and why brushing twice daily matters. The chapter also revisits the digestive and respiratory systems with more depth than Class 3, and reinforces the five senses. This is health science that directly impacts a child's daily habits — literally shaping how they eat and care for their body.

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My Body — Class 4 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 4 Science, Chapter 1. Internal organs, teeth and dental care.

1. About this chapter

This chapter covers My Body as part of the Class 4 Samacheer Kalvi Science curriculum. It deals with internal organs, teeth and dental care and builds conceptual understanding essential for the TN School Term Exam.

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

Name internal organs and their functions
Explain the importance of dental care

2. Key concepts

Concept 1: Name internal organs and their functions.
Concept 2: Explain the importance of dental care.

3. Important terms and formulas

Term / Formula	Description
Name internal organs and…	Name internal organs and their functions
Explain the importance of…	Explain the importance of dental care

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 my body.

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 1.
Give two real-life examples related to my body.
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 4 Science — Chapter 1: My Body.
Core idea: Internal organs, teeth and dental care.
Key outcomes: Name internal organs and their functions; Explain the importance of dental care.
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.

Types of teeth

Incisors (8) → front teeth, sharp edge, cut food like scissors. Canines (4) → pointed, next to incisors, tear food like a fork. Premolars (8) → flat surface with ridges, crush and tear food. Molars (12 including 4 wisdom teeth) → largest, broad flat surface, grind food like a mortar and pestle.

Teeth are the hardest substance in the human body — even harder than bone. The outer layer (enamel) is 96% mineral. Yet, sugar + bacteria in the mouth produce acid that can dissolve enamel, causing cavities.

Milk teeth vs Permanent teeth

Milk teeth (deciduous) → 20 teeth, start appearing at ~6 months, all 20 by age 3, start falling out at age 6-7, replaced by permanent teeth. Permanent teeth → 32 teeth (including wisdom teeth), start erupting at age 6-7, most by age 12-13. Wisdom teeth (4 molars) appear between ages 17-25.

The first permanent molar ('6-year molar') erupts behind the milk teeth at age 6 — many parents mistake it for a milk tooth and neglect its care. This tooth is crucial for proper bite alignment.

Digestive system pathway

Mouth (chewing + saliva begins starch digestion) → Oesophagus (food pipe, peristalsis pushes food down) → Stomach (churns food with acid and enzymes) → Small Intestine (main digestion + absorption of nutrients into blood; 6-7 metres long) → Large Intestine (absorbs water, forms faeces) → Rectum → Anus (waste exits).

The entire digestive journey from mouth to anus takes about 24-72 hours. The small intestine alone has a surface area of about 250 m² — roughly the size of a tennis court — because of tiny finger-like projections called villi.

Respiratory system pathway

Nose/nostrils → Nasal cavity (air warmed, filtered, moistened) → Pharynx (throat) → Larynx (voice box) → Trachea (windpipe) → Bronchi (two branches, one to each lung) → Bronchioles (smaller branches) → Alveoli (tiny air sacs where oxygen enters blood and CO₂ leaves).

The lungs contain about 300-500 million alveoli. If spread flat, they would cover about 70 m² — nearly the size of a badminton court. This large surface allows efficient gas exchange.

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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 only sugar causes cavities — ignoring frequency of eating

✓ It is not just HOW MUCH sugar you eat, but HOW OFTEN. Every time you eat, mouth bacteria produce acid for 20-40 minutes. Sipping a sugary drink slowly over 2 hours exposes teeth to acid for the entire 2 hours. Eat sweets at mealtimes, not as frequent snacks.

WATCH OUT

✗ Brushing teeth only in the morning — skipping night brushing

✓ Night brushing is MORE important than morning brushing. During sleep, saliva flow decreases, allowing bacteria to multiply freely. Food particles left overnight = 8 hours of bacterial feast. Always brush before bed.

WATCH OUT

✗ Confusing the windpipe (trachea) and food pipe (oesophagus)

✓ The trachea (windpipe) is in FRONT, has cartilage rings, and carries air. The oesophagus (food pipe) is BEHIND it and carries food. The epiglottis — a flap — closes the trachea when you swallow to prevent food from entering the lungs.

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