Mystery #4Tier 2body / skeleton

What's inside a bone?

From the outside a bone looks like a plain, solid white stick. But crack one open (as you might see in a soup bone) and there's a soft, jelly-like centre hidden inside. What is it, and what's it for?

A bone cut across the middle, showing the pale hard outer shell, the red spongy bone around it, and the softer marrow in the centre. — Photo: OpenStax Anatomy and Physiology · CC BY 4.0 · via Wikimedia Commons

Your guess

What's your hunch about the soft stuff in the middle of a bone, and what does it do?

There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.

Make a guess to unlock the hints and the answer.