The movement of oxygen from product of photosynthesis, through the human system, water, and Earth's atmosphere is a scientific model called the oxygen cycle. And it's essential for life on Earth to continue. Through accessible language and full-color diagrams and photographs, this book explains an important natural cycle to readers of all levels, particularly those struggling to understand a standard text book. Fact boxes and an extended glossary allow for the inclusion of the most important science vocabulary so all readers have the ability to understand, speak, and write about the topic.