Chapter 19 of 23

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Tamil Nadu (TNBSE)Class 8 Science★ 5-8 marks in the TN Class 8 annual exam through book-back MCQs, fill-ups and short answers

Movements in Animals

Samacheer Kalvi (TN State Board) Class 8 Science — Biology Chapter 19, Movements in Animals. The human skeleton, the types of joints (ball and socket, hinge, pivot, gliding, fixed), the ribs and vertebral column, how antagonistic muscles (biceps and triceps) move bones, and locomotion in other animals. Notes with the actual book-back questions, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

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

1Name the parts of the skeletal system
2Identify the types of joints and where they occur
3State the number of ribs and vertebrae and what they protect
4Explain how antagonistic muscles move bones
5Describe locomotion in other animals

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Why this chapter matters

Movements in Animals explains how the skeleton, joints and muscles work together to move the body, and how other animals move. The joint types, 206 bones, 12 pairs of ribs and antagonistic muscles are directly tested book-back content in the TN Class 8 exam.

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A 5-minute refresher here will save you 30 minutes of confusion below.

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Chapter 18 — Organisation of Life

Muscular and connective tissue.

Movements in Animals — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Biology — Chapter 19. Bones, joints and muscles that make us move.

1. About this chapter

This chapter covers the skeletal system, the types of joints, the ribs and vertebral column, how muscles move bones, and locomotion in other animals.

2. The skeleton and joints

The adult human skeleton has 206 bones. A joint is where two or more bones meet.
Types of joints:
- Ball-and-socket joint — allows movement in all directions; found in the shoulder and hip.
- Hinge joint — allows movement in one plane (back and forth); found in the elbow and knee.
- Pivot joint — allows rotation; between the skull and the neck (atlas–axis).
- Gliding joint — bones slide; found in the wrist and ankle.
- Fixed (immovable) joint — no movement; between the bones of the skull.

3. Ribs and the vertebral column

There are 12 pairs of ribs forming the rib cage, which protects the heart and lungs.
The vertebral column (backbone) has 33 vertebrae and protects the spinal cord.

4. Muscles and movement

Muscles can only pull (contract), not push, so they work in antagonistic pairs.
In the arm, the biceps (flexor) contracts to bend the elbow while the triceps (extensor) relaxes; to straighten the arm the triceps contracts and the biceps relaxes.

5. Movement in other animals

Earthworm — moves using muscles and bristles (setae).
Snail — creeps on a muscular foot.
Fish — a streamlined body and fins for swimming.
Bird — wings, hollow (light) bones and strong flight muscles for flying.

6. Worked examples

Example 1. Which joint is found in the shoulder? Ball-and-socket joint.

Example 2. How many pairs of ribs are there? 12 pairs.

Example 3. Which muscle bends the elbow? The biceps (flexor) — by contracting.

7. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

The joint in the elbow is a — (a) ball-and-socket / (b) hinge joint. Ans: (b) hinge.
The number of bones in the adult human body is — (a) 206 / (b) 300. Ans: (a) 206.
The biceps and triceps are — (a) antagonistic muscles / (b) the same muscle. Ans: (a) antagonistic.
The joint between the skull and the neck is a — (a) pivot / (b) gliding joint. Ans: (a) pivot.
The rib cage protects the — (a) brain / (b) heart and lungs. Ans: (b) heart and lungs.

II. Fill in the blanks 6. There are 12 pairs of ribs in the human body. 7. The bones of the skull form a fixed (immovable) joint. 8. A muscle can only pull (contract), not push.

III. Answer briefly 9. What are antagonistic muscles? Give an example. 10. Name the joint found in the hip and the type of movement it allows.

8. Common mistakes

Mistake: Saying muscles can push. Fix: Muscles only pull (contract); they work in antagonistic pairs.
Mistake: Calling the elbow a ball-and-socket joint. Fix: The elbow is a hinge joint; the shoulder/hip are ball-and-socket.
Mistake: Giving 300 bones for an adult. Fix: An adult has 206 bones (a baby has more, which fuse).

9. Quick revision

Biology Ch 19 · skeleton, joints, muscles.
206 bones; joints: ball-and-socket (shoulder/hip), hinge (elbow/knee), pivot (neck), gliding (wrist), fixed (skull).
12 pairs of ribs protect heart and lungs; 33 vertebrae protect the spinal cord.
Muscles only pull → antagonistic pairs; biceps (flexor) bends, triceps (extensor) straightens.
Other animals: earthworm (setae), snail (foot), fish (fins), bird (wings, hollow bones).

Key formulas & results

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

Skeleton

206 bones; joint = where bones meet

Framework of the body.

Joints

ball-and-socket · hinge · pivot · gliding · fixed

Shoulder/hip, elbow, neck, wrist, skull.

Protection

12 pairs of ribs; 33 vertebrae

Heart/lungs; spinal cord.

Muscles

antagonistic pair (biceps flexor + triceps extensor)

Muscles only pull.

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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

✗ Saying muscles can push

✓ Muscles only pull (contract); they work in antagonistic pairs.

WATCH OUT

✗ Calling the elbow a ball-and-socket joint

✓ The elbow is a hinge joint; the shoulder/hip are ball-and-socket.

WATCH OUT

✗ Giving 300 bones for an adult

✓ An adult has 206 bones (a baby has more, which fuse).

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on joints, bone count, muscles and the rib cage.

Questions

Fill in the blanks

Ribs, fixed joint and muscle action.

Questions

Answer briefly

Antagonistic muscles, joints, locomotion in animals.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

The joint in the elbow is a ____ joint.

▶ Show solution

hinge.

Q2EASY· MCQ

The number of bones in the adult human body is ____.

▶ Show solution

206.

Q3EASY· MCQ

The joint between the skull and the neck is a ____ joint.

▶ Show solution

pivot.

Q4EASY· Fill in the blanks

There are ____ pairs of ribs in the human body.

▶ Show solution

12.

Q5MEDIUM· Answer briefly

What are antagonistic muscles? Give an example.

▶ Show solution

A pair of muscles that work in opposite directions — when one contracts the other relaxes. Example: the biceps (flexor) bends the elbow while the triceps (extensor) relaxes, and vice versa.

Q6EASY· Answer briefly

How does an earthworm move?

▶ Show solution

It moves by alternately contracting and relaxing its muscles, gripping the soil with tiny bristles called setae.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Biology Chapter 19 of Samacheer Kalvi Class 8 Science.
•206 bones; a joint is where bones meet.
•Joints: ball-and-socket (shoulder/hip), hinge (elbow/knee), pivot (neck), gliding (wrist), fixed (skull).
•12 pairs of ribs protect heart and lungs; 33 vertebrae protect the spinal cord.
•Muscles only pull, so they work in antagonistic pairs (biceps + triceps).
•Other animals: earthworm (setae), snail (foot), fish (fins), bird (wings, hollow bones).

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 5-8 marks across book-back MCQ, fill-ups and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Fill	1	3-5	Joints, bone count, ribs
Short Answer	2-3	1-2	Antagonistic muscles, joint types
Application	2	1	Locomotion in other animals

Prep strategy

Match each joint to its body location
Remember 206 bones, 12 pairs of ribs
Learn the biceps–triceps antagonistic pair
Note how earthworm, snail, fish and bird move

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Health

Knowing joints helps treat sprains, fractures and arthritis.

Sports

Antagonistic muscles explain exercise and training.

Robotics

Robot joints and actuators copy ball-and-socket and hinge designs.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Match joints to body parts with examples
Quote 206 bones and 12 pairs of ribs
Explain biceps/triceps as an antagonistic pair
Name locomotion structures for other animals

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Identify the joint at the jaw, fingers and backbone.
Explain why a streamlined shape helps a fish move through water.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

A muscle can only pull when it contracts, not push back. So muscles are arranged in antagonistic pairs — one pulls a bone one way, and its partner pulls it back.

Hollow, air-filled bones make the skeleton light, which helps the bird fly while still being strong enough for flight muscles.

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