Signal transduction is the process by which cells respond to external signals, such as hormones or nutrients. When a signal molecule, like a hormone, binds to a receptor on the cell's surface, it triggers a series of events inside the cell. This can lead to changes in gene expression, enzyme activity, or even cell movement, allowing the cell to adapt to its environment. The entire process involves various proteins and pathways, often referred to as signaling pathways. These pathways can amplify the signal, ensuring that even a small amount of the signal molecule can produce a significant response. Ultimately, signal transduction is crucial for maintaining cellular functions and communication.