They're called omnivorous. In one way or another, animals are dependent on plants for nutrition. They also rely on plants for valuable oxygen, essential to the respiration process. As they breathe, animals take in oxygen and give off carbon dioxide. Plants, in turn, use the carbon dioxide in photosynthesis, and the cycle goes on.
Photosynthesis is the foundation of all food chains.
It's the basic building block for life on earth. A food chain is a series of organisms that are interrelated and dependent according to their feeding habits, with the smallest or lowest form fed on by a larger one, and that one in turn eaten by a larger one, and so on to the top of the chain. A food web is more complex than a food chain. The leaves of land plants are the parts best equipped to carry on photosynthesis. They contain chlorophyll, trap sunlight for energy, and absorb carbon dioxide through hundreds of tiny pores known as stomata.