The Skeleton and Muscles (KS2 Science)

SC4The Skeleton and Muscles

A frame that supports, protects and moves you.

The skeleton supports the body, protects organs, and works with muscles to create movement.

Three jobs of the skeleton.

🏗️ Support
Bones hold the body up and give it shape — without them we'd collapse.

🛡️ Protection
The skull guards the brain; the ribcage shields the heart and lungs.

🏃 Movement
Muscles pull on bones at joints to move us.

Muscles PULL, never push — so they work in pairs to move a joint both ways.

Learn the System

1Bones give a rigid frame.

Over 200 bones, made of living tissue. Joints (knee, elbow, shoulder) are where bones meet and can move.

bones + joints

2Muscles pull on bones.

Attached to bones by tendons, a muscle shortens (contracts) to pull a bone — it cannot push.

contract = pull

3Pairs work together.

To bend AND straighten the elbow, muscles work in pairs: the biceps bends it, the triceps straightens it. One relaxes as the other contracts.

biceps ↔ triceps

💡 Key IdeaBecause a muscle can only pull (contract), not push, movement needs antagonistic pairs — one to bend a joint, its partner to straighten it.

Worked Example

What happens in your arm when you bend your elbow to lift a cup?

Biceps

contracts (shortens) and pulls the forearm up

→

Triceps

relaxes to allow the bend

→

✓ To straighten

triceps contracts, biceps relaxes — the pair reverses

Watch Out! Common Mistakes

‘Muscles push.’

Only pull! A muscle shortens to PULL a bone. To move a joint the other way, a DIFFERENT muscle pulls — that’s why they come in pairs.

‘Bones are dry and dead.’

Bones are alive! They contain living cells, blood vessels and marrow, and can grow and repair.

Confusing tendons and muscles.

Tendons connect! Tendons are the strong cords joining muscle to bone; the muscle is the part that contracts.

⬇ Cheat Sheet

THE SKELETON AND MUSCLES

Skeleton: support, protection, movement.
Bones meet at joints; bones are living tissue.
Muscles pull (contract) — never push.
Antagonistic pairs (biceps/triceps) move joints both ways.

Example: bending the elbow — biceps contracts, triceps relaxes.

📖 Continue Your Journey

✓ SC1 Classifying Living Things ✓ SC2 Habitats and Adaptation ✓ SC3 Food Chains and Webs SC4 The Skeleton and Muscles SC5 Digestion and Teeth SC6 The Circulatory System SC7 Plants and Photosynthesis SC8 Life Cycles and Reproduction SC9 States of Matter and the Water Cycle SC10 Materials and Their Properties SC11 Reversible and Irreversible Changes SC12 Forces and Magnets SC13 Light and Shadows SC14 Sound SC15 Electricity and Circuits SC16 Earth and Space

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Next Lesson: SC5 Digestion and TeethFrom plate to energy.

📄 Free printable: Download the The Skeleton and Muscles cheat sheet (PDF) — keep it by your child's desk.

Quick summary

The skeleton supports the body, protects organs and enables movement.
Bones are living tissue and meet at joints.
Muscles contract to pull on bones — they cannot push.
Antagonistic pairs like biceps and triceps move a joint both ways.

Frequently asked questions

What are the three jobs of the skeleton?

Support (holding the body up), protection (the skull guards the brain, ribs guard the heart and lungs) and movement (working with muscles).

Why do muscles work in pairs?

Because a muscle can only pull by contracting, not push. One muscle bends a joint and its partner straightens it — like the biceps and triceps at the elbow.

Are bones alive?

Yes — bones are living tissue with cells, blood vessels and marrow, able to grow and repair after breaks.

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