Ecosystems receive their energy from the Sun. The energy from sunlight is converted into sugar by plants, algae, and photosynthetic bacteria. They use this energy to grow and to support their vital functions. The sugar produced by these organisms also forms the energy source of all the other organisms of the ecosystem.

Plants and algae are producers, as they use energy from the Sun to produce energy for their ecosystems. They do this through the process of photosynthesis.

Photosynthesis occurs in the chloroplasts  of plant cells. To photosynthesize, a producer needs light energy from the Sun, water, and carbon dioxide. Because sunlight is essential to producers, plants do not live in environments where sunlight is not available. 

To receive enough sunlight, aquatic plants often live near the surface of the water. Aquatic plants have no problems in receiving enough water to photosynthesize, but the amount of carbon dioxide in water is often quite limited. Aquatic plants receive carbon dioxide directly from water. If plants photosynthesize too efficiently, the resulting lack of carbon dioxide can become a limiting factor. Aerial shoot plants and floating-leaf plants gather carbon dioxide from the air.

Photosynthesis produces sugar and oxygen. Both of these substances are essential to the organisms of all ecosystems. The plants use most of the sugar themselves to grow and reproduce. Plants use some of the produced oxygen themselves as well, but release the majority of it into the environment, where it is used by other organisms.

To grow, producers also need nutrients. They are chemical substances that plants need in order to grow. Nitrogen and phosphorous are two of the most important plant nutrients. Normally, these nutrients circulate through the ecosystem.