What Makes a Plant Bend Toward the Light?
Plants usually bend toward the light because cells on the shaded side of a stem grow faster than the cells on the sunny side. Therefore, the tip of the stem curves toward the light. A plant hormone called auxin is responsible for the growth of plants toward light. This chemical is produced in the growing tips of plants.
When light falls on the side of a plant stem, the auxin tends to move away from the light. Auxin then accumulates in the shaded side of the stem, speeding up growth on that side. This causes the stem to bend gradually toward the light. The concentration of auxins on the dark side may be due to the fact that sunlight slows or kills auxin when light falls on them. However, as long as one part of the plant gets sunlight, it can make food and the whole plant survives.
Plants Bend toward Light due to a phenomenon called phototropism. Phototropism is one of the many plant movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. We now know what occurs in the first and last stages of phototropism, but still need to understand how lateral auxin distribution actually occurs.