Answer:
phytoplankton; diffusion
Explanation:
"Phytoplankton" takes the role of the plant in the marine environment because it consists of tiny plants that contain chlorophyll–just like the terrestrial plants. This provides food to many aquatic animals in the ocean.
When it comes to carbon cycle, carbon dioxide from the atmosphere is being diffused into the ocean by dissolving it. The carbon in the ocean turns into an organic matter through the process of photosynthesis. The ocean is said to have more carbon compared to the atmosphere because many marine animals use it for survival.