Final answer:
The basic food source for all organisms is plants. They capture energy from the sun and convert it into food through photosynthesis.
Step-by-step explanation:
The basic food source for all organisms is plants. Plants, such as trees and grasses, capture energy from the sun through a process called photosynthesis and convert it into organic molecules, which serve as food for other organisms.
Fungi, on the other hand, survive by absorbing nutrients from other organisms or their remains.
In an ecosystem, organisms are classified into different trophic levels. The trophic levels represent the position of organisms in the food chain or web, based on how they obtain energy. Producers, like plants, occupy the first trophic level as they can directly capture energy from the sun and convert it into food through photosynthesis.