Animals cannot produce their own food. All animals depend on plants for food explicitly or implicitly. Plants, in presence of light and water, produce their own food by the process of photosynthesis with the help of Chlorophyll.
Plants use these foods for their own survival. Animals also depend upon this food, as they are not able to produce their own food. Thus all animals of this world are depending directly or indirectly on plants. In food producing system by plants carbon dioxide is used which is produced by the respiration of animals.
The green plants intake Carbon dioxide and release Oxygen to the environment during the by process of photosynthesis. All animals release excreta. When an animal dies it is disintegrated into the soil and enriches its fertility. This is essential for plant survival.
The pollination of plants is dependent upon insects. birds etc. There arc many plants that house various insects and birds. These animals depend on plants for their food. Thus it can be understood how plants and animals are interdependent for survival.