Depictions of the various organisms are not to scale. The food web is a simplified way of understanding the process by which organisms in higher trophic levels gain energy by consuming organisms at lower trophic levels. All energy in an ecosystem originates with the sun. The solar energy is transformed by green plants through a process of photosynthesis into stored chemical energy. This is consumed by plant-eating animals, which are in turn consumed as food.
Humans are part of the food web.
The concept of the food web explains how some persistent contaminants accumulate in an ecosystem and become biologically magnified. In order to obtain sufficient quantities for growth, phytoplankton must collect these chemical elements from a relatively large volume of water. In the process of collecting nutrients, they also collect certain human-made chemicals, such as some persistent pesticides. These may be present in the water at concentrations so low that they cannot be measured even by very sensitive instruments. The small fish and zooplankton eat vast quantities of phytoplankton.