eli5: How do plants “know” which direction to grow in (to catch most light)?

Question

I recently put a new plant by my window, and within a week it had grown “lopsided”. The leaves nearer the window were much bigger and all the leaves were angled to face the window.
It makes sense since all the light is coming from one direction, but how did it know that?
Is there a central “brain” which tells the leaves to grow that way? Or is it something about the leaves themselves that makes them do that?

In: Biology

Answer 1

The side of the stem which gets less light grows more, which makes the stem bend. The phenomenon has a scientific name, but I can’t recall what it is.