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An adult skeleton usually has 206 bones in two groups: the axial skeleton (80 bones: skull, backbone, ribs and breastbone) and the appendicular skeleton (126 bones: arms, legs and the girdles that join them on).

The skeleton has five jobs: support, movement, protection, storing minerals such as calcium and phosphorus, and making blood cells in the red marrow.

Bones come in five shapes. Long bones (thigh bone, upper-arm bone, finger bones) work as levers. Short bones are in the wrist and ankle. Flat bones (skull, ribs, shoulder blades, breastbone) protect organs and anchor muscles. Irregular bones include the vertebrae. The kneecap is a sesamoid bone inside a tendon.

Experiment: Paper bones: which shape is strongest?

1. Question: does the shape of the same sheet of paper change how much weight it can hold? Predict which shape will hold the most books.
2. Make three 'bones' from identical sheets: a flat sheet folded in half to stand up like a tent, a sheet folded into a zigzag, and a sheet rolled into a tube about 3 cm wide and taped.
3. Fair test: same paper, same height, same card on top, books added one at a time, gently and in the centre.
4. Stand one 'bone' upright, put the card on top and add books until it collapses. Record the number of books it held.
5. Repeat each shape three times with new sheets and work out the mean. Which shape won?

Shape	Books (try 1)	Books (try 2)	Books (try 3)	Mean
Tent (folded)	Which shape will hold the most books?
Zigzag	Which shape will hold the most books?
Tube	Which shape will hold the most books?

Questions

1. Name the five jobs of the skeleton.

2. Draw a long bone cut in half. Label compact bone, spongy bone and marrow.

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3. Which paper shape held the most books? Use your results to explain why long bones are tube-shaped.

4. Why do children need calcium and active play while they are growing?

Sources for every fact on this sheet: echoesof.science/school/skeleton/sources/

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