|sprounds reaching towards the light source|
Why does this happen? Well this phenomenon is called phototropism. The process is not yet fully understood by scientists, but current models say that there's a hormone called auxin in plants, which releases H+ ions to the unlit tissues of the plant. The pH value decreases and the cell walls are acidified and therefore weakened. This turn of events also activates an enzyme expansins, who also breaks the cell walls. As they become fragile, gravity takes over and the whole plant bends towards the direction of the light source. As thousands of these processes occur all over the plant, it forms the movement we have come to know as photoropism.