Producers in most ecosystems rely primarily on which energy source?

• A. Chemical energy
• B. Soil nutrients
• C. Sunlight
• D. Water

Answer: (C)

Sunlight provides the energy that powers most ecosystems. Producers like plants, algae, and some bacteria capture light with chlorophyll and use it to drive photosynthesis, turning light energy into chemical energy stored in sugars. That chemical energy becomes the food for all other organisms in the food web. While soil nutrients support growth and water is needed for the chemical reactions, they do not supply energy the way sunlight does. There are some environments, such as around deep-sea vents, where organisms rely on chemical energy from inorganic molecules, but in most ecosystems, sunlight is the primary energy source.