A food chain is a sequence of transfer of food and energy when one organism is consumed by another organism.
A food chain is always unidirectional sequence.
In the provided food chain the sun is the source of energy required for the preparation of food by the phytoplankton that is an aquatic autotroph which will prepare its food by the process of photosynthesis.
The phytoplankton being producer of biomass is consumed by the zooplankton that is the primary consumer than the zooplankton will be consumed by the fish that is the secondary consumer and carnivore by origin and finally the fish will be consumed by the bear that is also carnivore and is tertiary consumer.
