Answer: Diatom
Step-by-step explanation:
A photoautotrophic primary producer is an organism which can synthesize its own food by the process of photosynthesis. This producer lies at the base of the food chain being first trophic level of the food chain.
Diatom can be defined as the single-celled photoautotrophic primary producer. They can be found in both freshwater and marine water ecosystems. These are eaten up by zooplanktons, shrimps and other aquatic organisms.