The answer is c. in the photic zone. Plankton is a diverse group of organisms that live in the water and not capable of active swimming. Phytoplankton includes a diverse autotrophic group of organisms. Since they are autotrophic, they produce their own food in the process of photosynthesis. Light is important for photosynthesis and phytoplankton tends to live in the photic zone which receives sunlight.