Phototropism is a biological response exhibited by plants in which they grow or bend towards a source of light. This phenomenon allows plants to optimize their exposure to sunlight, which is essential for photosynthesis, a process that enables them to convert light energy into chemical energy for growth and development.

Key points about phototropism:

1. Positive Phototropism: Plants exhibit positive phototropism when they grow or bend toward a source of light. This movement is more prominent in the stems and leaves, as these parts are responsible for capturing sunlight.
2. Auxins: The growth hormone auxin, particularly a type called indole-3-acetic acid (IAA), plays a crucial role in phototropism. When light strikes the plant from one side, auxin accumulates on the shaded side.
3. Differential Growth: The accumulation of auxin on the shaded side of the plant stem leads to differential growth. Cells on the shaded side elongate more rapidly than those on the illuminated side.
4. Bending Toward Light: As a result of this differential growth, the stem or plant part bends or grows in the direction of the light source. The elongation of cells on the shaded side causes the bending.
5. Advantages: Phototropism is an adaptive response that allows plants to orient themselves towards sources of light, ensuring that they can capture more sunlight for photosynthesis. This enhances their overall growth and reproductive success.
6. Examples: Some classic examples of phototropism include seedlings bending towards a window to get more light or sunflowers tracking the movement of the sun across the sky.