The process of cellular communication is called signal transduction. This complex mechanism allows cells to respond to external stimuli through various types of signals, including hormones, neuronal signals, and chemical messengers. When a signal binds to a receptor on a cell’s surface, it triggers a cascade of biochemical reactions inside the cell, often involving second messengers or protein phosphorylation. This process ultimately leads to specific cellular responses, such as gene expression, cell growth, or apoptosis. Effective cellular communication is essential for maintaining cellular functions and homeostasis in multicellular organisms.