Which gas do animals exhale that plants require for photosynthesis?

Animals exhale carbon dioxide, which is crucial for the process of photosynthesis in plants. During photosynthesis, plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This gas, which is a byproduct of cellular respiration in animals, provides the carbon source that plants need to synthesize their food. The interdependence of animals and plants is a key aspect of ecosystems, with animals contributing carbon dioxide to the environment, enabling plants to produce oxygen and sustain life.