What role does the Sun play in ecosystems?

The Sun serves as a primary energy source in ecosystems, which is fundamental to the process of photosynthesis. Plants, the primary producers in most ecosystems, utilize sunlight to convert carbon dioxide and water into glucose and oxygen. This process not only supports the plants themselves but also provides energy that is passed through the food web, from herbivores that eat the plants to predators that eat the herbivores. The Sun's energy drives climate systems and weather patterns, which are crucial for sustaining various habitats and the biodiversity within them. Thus, the role of the Sun as the primary energy source is essential for the survival of most life forms on Earth, highlighting its critical function in ecosystems.

The other options do not accurately capture the Sun’s primary role within an ecosystem, as cooling the atmosphere, providing nutrients, or watering plants directly do not convey the foundational aspect of solar energy that fuels the vast majority of biological processes.