Answer: b. phytoplankton ® zooplankton ® fish ® mammal
Phytoplankton are single celled organisms they are included in the category of bacteria, protist or algae living in an aquatic biome. They are autotrophic in nature. Examples are cynobacteria, diatoms etc. They are abundant in number and maintains the lowest level in aquatic food chain, they are the primary producers as they can produce their own food. This level has the highest energy in the aquatic food chain. Zooplankton are aquatic organisms which are heterotrophic in nature. They are dependent upon plants and other aquatic organisms for their living. Examples Dinoflagellates, Cnidarians, Crustaceans, Chordates, Molluscs etc. They are the primary consumers in the aquatic ecosystem. Fishes are dependent upon both phytoplanktons and zooplanktons for their food requirement, they are dependent upon primary producers and primary consumers. Therefore, they are secondary consumers in the aquatic food chain. Lastly, mammals feed on fish are tertiary consumers. Therefore, energy will flow from primary producer to primary consumer, then to secondary and tertiary consumers. The lowest level in food chain will attain largest energy and the highest trophic level will attain the least energy. This is in accordance with the 10% law which says that energy decreases at each subsequent trophic level starting from the bottom.
Hence, the energy will flow in phytoplankton ® zooplankton ® fish ® mammal
