Isotope labelling is a technique used in various fields of science, such as chemistry, biochemistry, and environmental science, to track the movement of atoms or molecules within a system. Isotopes are atoms of the same element that have a different number of neutrons, resulting in different atomic masses. By introducing isotopically-labeled atoms or molecules into a system, researchers can trace their movement and interactions with other atoms or molecules. Isotope labelling is commonly used in metabolic studies to track the pathways of specific molecules within organisms, such as the synthesis and breakdown of proteins, carbohydrates, and lipids. It can also be used to study nutrient cycling in ecosystems, monitor pollution sources, and investigate chemical reactions in various industrial processes. Overall, isotope labelling provides a powerful tool for understanding complex systems by allowing researchers to follow the movement of specific atoms or molecules with high precision and accuracy.