Each lab takes one mechanism apart across levels. It builds a twin world with one thing changed, walks you from the world down to cells or molecules and back up, and waits until the world shows you the effect. Then, below, make the call on situations you haven't seen.
Situations, not definitions. Guessing before you try the lab is fine: a wrong answer explains itself, and the lab it comes from is linked.
Progress is kept in this browser only and is never sent anywhere.