How are plants and animals related?
The waste product produced by photosynthesis is oxygen, the gas that all animals need to breathe. So without plant life, there would be no animal life on Earth. And without plants around to absorb carbon dioxide, an excess amount of this gas would linger in our atmosphere, trapping the Sun's heat and causing an unwanted increase in the planet's average temperatures. Plants, then, are essential not only because they provide so much of the food people eat (and provide nourishment for many of the animals we eat), but because they make the air healthier, using up carbon dioxide and releasing oxygen. In addition, we depend on plants to provide us with other things we need, like wood for building, fibers for making clothes, and medicines to improve our health.