The given blank can be filled with Consumer.
In an ecosystem, the producers are the members, who are make their own food by using sunlight. Mainly the green plants are the producers, they produce their own food by the process of photosynthesis.
The consumers are the organisms, who consume the food made by the producers. The source of energy for these organisms are the producers. The energy from producers is transferred to the consumers. So, energy always flows from producers to consumers.
5: the parasite and the host need each other
