Final answer:
A primary producer is located at the first step of a food chain, known as the 1st trophic level, where it serves as the base and source of energy for all other consumers in the ecosystem.
Step-by-step explanation:
In a food chain, primary producers would be located at the first step, which is also known as the 1st trophic level. Primary producers are photosynthetic organisms such as plants or phytoplankton that form the base of the food chain.
They are the ones who capture energy from the sun and convert it into food through photosynthesis, providing the energy source for the rest of the food chain.
Following primary producers are primary consumers, which are herbivores that eat the producers. Secondary consumers, usually carnivores, feed on primary consumers, and this continues up the trophic levels to the apex consumers at the top.
Without primary producers, a food web cannot be sustained as they are the basal energy source for all other consumers in the ecosystem.