Sunflower heads move toward the sun. This is an example of?

The correct answer is phototropism, which refers to the growth or movement of a plant in response to light direction. In the case of sunflowers, this phenomenon is particularly evident as their heads, or flower buds, orient themselves toward the sun throughout the day to maximize light absorption. This optimized positioning enhances photosynthesis, allowing sunflowers to capture more sunlight to fuel their growth and energy needs.

Photosynthesis is the process by which plants convert light energy into chemical energy, specifically glucose, using carbon dioxide and water, but it does not directly describe the movement of the plant toward light. Photoperiodism refers to how plants respond to changes in the duration of light and dark periods, influencing flowering and growth cycles, but does not involve movement toward a light source. Osmosis is the process of water movement through a semipermeable membrane, which is unrelated to the directional growth response of plants to light. Thus, phototropism effectively explains the sunflower's behavior of turning its head toward the sun.