Chelates or chelating agents are (typically organic) chemical compounds bound to a central metal ion. In biology chelates play roles in biochemical reactions, for example chlorophyll is one of the most important chelates in nature that channels sunlight energy into chemical energy – the process called photosynthesis. Another important chelate is porphyrin – which binds four oxygen molecules to hemoglobin in red blood cells, delivering them from lungs (or gills) to tissue cells to provide energy.