Why do plants grow towards the sun?

Plants are all around us and chances are you've come across a few in your life. Also we've heard countless times that "without sun, plant's couldn't grow". I won't get into why they actually need sun light to grow and what processes happen, let's just take it for a fact now. Most plants are adapted to absorb as much light rays as possible, they grow wide and thin leaves and in such a manner that the leaves would not block the sun for other ones. Another adaptation is that parts of the plant turn to the sun - the blossom, the leaves, even the stem.

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.