where does an animal's food come from ?

This depends upon the diet of the animal. If it is a carnivore, like a wolf, tiger, then the foods will come from the fresh and blood of other animals which their eats. If the animal is herbivore, like deer, rabbit, then the foods will come from the leaves, fruits or the roots of plants which their eats. So where do plants get their food from ?

Green plants are quite different from animals. They do not take their food from other living organisms ( expect for several of eating plants).
Plants takes water and minerals from the soil and they take carbon dioxide gas from the air. Then these green plants use the energy in sunlight to make their own food by photosynthesis.

The sugar, oils, and proteins that the green plants makes for itself is organic matter that it may use for growth. That is to say the plant may use this food to build new leaves, flowers and roots. some of the plant's food, however, may be used for respiration. The energy released by respiration allows the plant to live.

Finally, some parts of the plant may die and are lost, for example the leaves that fall from trees in autumn.

Therefore , the plants make their own food by photosynthesis.
The herbivores feed upon the leaves, roots and other parts that the plant grows.

The carnivores feed upon the muscles and blood that the herbivore grows.

When animals and plants respire they release carbon dioxide into the atmosphere. when they produce wastes or when they die their dead bodies return the minerals to the soil.

The decomposers such as the fungi and the bacteria play an important role in returning these minerals to the soil.

This means that the chemicals in our bodies were once part of a plant. When we die these chemicals will be taken up by the roots of a plant once again. Therefore the chemicals that living plants are made of constantly being recycled .