Cellular responses refer to the manner in which a cell responds to extracellular signals. These may be caused by signals from the cell itself, signals from neighboring cells, or changes in the extracellular environment. Each signal activates a specific receptor, which initiates transduction and specific cellular responses. 

Cellular responses may occur at the molecular level or macroscopic level. Most common cellular responses include: 

• Changes in gene expression
• Structural changes in cell shape or size
• Cell growth or division
• Cell death or apoptosis
• Changes in motility
• Changes in protein activation