Figure 1: Oxygen Carbon Dioxide Cycle Uno ME Guide Questions: 1. What role does the horse play in the cycle? 2. How does the tree utilize carbon dioxide? 3. If the tree dies, what effect would it have to the horse? 4. Why is this natural process called a cycle?

2.Trees—all plants, in fact—use the energy of sunlight, and through the process of photosynthesis they take carbon dioxide (CO2) from the air and water from the ground. In the process of converting it into wood they release oxygen into the air.

3.No life is possible on the earth without plants. Life could not exist on Earth without trees because they produce most of the oxygen that humans and wildlife breathe. Trees absorb carbon dioxide from the atmosphere and release oxygen using the process of photosynthesis. There would also be no rain without trees.

4.A natural process in which elements are continuously cycled in various forms between different compartments of the environment (e.g., air, water, soil, organisms). Examples include the carbon, nitrogen and phosphorus cycles (nutrient cycles) and the water cycle.