Peel your body apart one layer at a time, the way the clear plastic pages work in an old anatomy book. Tap any circle on the figure to find out what lives there.
A baby is born with about 300 bones, many of them soft and separate so the baby can squeeze, bend and grow. As you get older some of those pieces fuse together into single bones, so the count goes down, not up.
A muscle can only pull. It can never push. That is why muscles always come in pairs. Press the button and watch which one does the work.
Tap to start, then wait. The moment the box turns green, tap it as fast as you can. What you measure is light reaching your eye, a signal racing to your brain, your brain deciding, and the order travelling all the way back down to your finger.
Breathe in as the circle grows, out as it shrinks. This pace is deliberately slower than normal, which is why it calms you down. Sitting still, most children breathe about 20 times a minute, roughly 20,000 times a day, without ever deciding to.
Every question from this lesson is in the Body 101 arena. Race the clock, duel someone at home, play as a team, beat the bosses, or practise with no timer at all.