Advanced Placement (AP) Biology Practice Exam

Signal transduction refers to the mechanism linking stimuli to cellular responses. This process involves a series of molecular events and pathways that transmit signals from the outside of a cell to its interior, ultimately prompting a specific response.

When an external signal, such as a hormone or neurotransmitter, binds to a receptor on the cell surface, it triggers intracellular signaling cascades that may involve various second messengers, protein modifications, and activation of specific genes. This sequence of events is crucial for cells to respond to their environment, regulate their internal processes, and communicate with other cells.

Understanding this process is fundamental to many biological functions, including growth, immune responses, and cell communication. The other options do not encompass the full concept of signal transduction, as they either describe specific actions or processes that may be involved but do not capture the overarching mechanism of transforming an external signal into a cellular response.