How do plants manage to turn towards the light?

It is easy to think of plants as inert life forms that simply sit at one place, soaking up sunlight and water. Yet plants are capable of some complex behavior. For example, plant gradually turn towards light sources to maximize the amount of energy they generate by photosynthesis—the process that takes place only when a plant is exposed to light. This inexorable orientation towards light is known as photot­ropism, which involves necessary adjustments to be made by the plant as it grows. The plant doesnot bend over as we humans do when we touch our toes; instead, it bends by growing in aparticular direction to reach out for light.A plant's growth move­ments are controlled by internal chemical substances When one side of a plant is in shade, a growth hormone called auxin moves to the darker side of the plant and causes that side to grow much faster. As can be seenin the accompanying illustra­tion, more cells are produced in that side of the stem. Asa result, the stem becomes bent towards the light. A house plant set on a windowsill soon turns towards the outside and has to be rotated to maintain its shape.