What is the basic food source for all organisms?

The basic food source for all organisms is plants, primarily due to their role in photosynthesis. Plants are autotrophs, meaning they produce their own food using sunlight, carbon dioxide from the air, and water from the soil. This process converts light energy into chemical energy stored in glucose, which serves as a fundamental energy source within the food chain.

Other organisms, including animals, fungi, and bacteria, are heterotrophs that cannot produce their own food and instead rely on consuming plants or other organisms. While animals consume plants (and other animals), fungi decompose organic material, and bacteria can either decompose or consume organic material depending on their type, plants remain the primary producers that capture solar energy and convert it into forms that are accessible to various life forms.

Thus, the correct answer reflects the foundational role of plants in the ecosystem as the primary producers that form the basis of most food chains.