The article discusses the importance of elemental stoichiometry in understanding the relationships between cellular, ecosystem, and evolutionary processes. It highlights the need for a unified approach to ecosystem science and evolutionary biology, especially in light of global biodiversity loss and changes in biogeochemical cycles. Elemental stoichiometry provides a new tool to trace the causal mechanisms linking these processes, offering a multi-currency approach that complements energy-based models. The article emphasizes the role of body nitrogen:phosphorus (N:P) ratio in modulating secondary production and nutrient cycling in ecosystems. It reviews the biochemical composition of key molecules and their elemental content, and explores how organismal characteristics such as growth rate and ontogeny are linked to biochemical and cellular investment, influencing body N:P ratio. The article also discusses how variations in body N:P ratio affect nutrient cycling and food quality constraints. It highlights the importance of understanding the stoichiometry of organisms in predicting patterns of nutrient cycling and food quality constraints. The article concludes that elemental stoichiometry provides a framework for integrating evolutionary biology, ecosystem science, ecology, and cell biology, offering a new perspective on the mechanisms driving ecosystem processes. The study of stoichiometry in biological processes is just beginning, but it has the potential to provide new insights into the relationships between cellular, ecosystem, and evolutionary processes.The article discusses the importance of elemental stoichiometry in understanding the relationships between cellular, ecosystem, and evolutionary processes. It highlights the need for a unified approach to ecosystem science and evolutionary biology, especially in light of global biodiversity loss and changes in biogeochemical cycles. Elemental stoichiometry provides a new tool to trace the causal mechanisms linking these processes, offering a multi-currency approach that complements energy-based models. The article emphasizes the role of body nitrogen:phosphorus (N:P) ratio in modulating secondary production and nutrient cycling in ecosystems. It reviews the biochemical composition of key molecules and their elemental content, and explores how organismal characteristics such as growth rate and ontogeny are linked to biochemical and cellular investment, influencing body N:P ratio. The article also discusses how variations in body N:P ratio affect nutrient cycling and food quality constraints. It highlights the importance of understanding the stoichiometry of organisms in predicting patterns of nutrient cycling and food quality constraints. The article concludes that elemental stoichiometry provides a framework for integrating evolutionary biology, ecosystem science, ecology, and cell biology, offering a new perspective on the mechanisms driving ecosystem processes. The study of stoichiometry in biological processes is just beginning, but it has the potential to provide new insights into the relationships between cellular, ecosystem, and evolutionary processes.