Plants are the basis of nearly all ecosystems on Earth because they carry out the process of photosynthesis. Plants harvest light energy from the sun and store it as potential chemical energy. When plants are eaten or die, their stored energy becomes available to other organisms. And when predators eat those other organisms, the energy flows into them. Each level at which energy is stored in organisms is called a . When an organism eats a plant, the energy and nutrients stored in the consumed organism flows up to the . This movement of energy through food chains is why models represent plants as the __of a food chain or food web.

All living organisms require energy for their life processes, which they obtain by taken in food. In an ecosystem, this food is derived when organisms feed on each other. This process that eventually leads to a flow of energy within organisms is called FOOD CHAIN.

A food chain or food web always begins with a unique set of organisms called PRODUCERS. Producers are autotrophs capable of harvesting light energy from the sun and use it to produce their food (chemical) in a process called PHOTOSYNTHESIS. Other organisms called HETEROTROPHS feed on these producers to derive energy. In ecology, they are called CONSUMERS. Other consumers feed on the previous ones also to get energy.

Hence, each step of the food chain is occupied by organisms that obtain and store energy by feeding on another organism. This step is called TROPHIC LEVEL.

In a nutshell, a PRODUCER (usually plants) starts the food chain/web due to its photosynthetic ability. This producer gets eaten by an organism called CONSUMER and in the process, the energy and nutrient stored in the producers flows to the consumer. Another consumers feeds on the previous one and the energy keeps flowing. Each step of the food chain occupied by an organism that stores and transfers this energy is called TROPHIC LEVEL.