Which statement about cell signaling is correct? Choose one: A. Each type of extracellular signal molecule induces the same response in all target cells. B. All extracellular signal molecules act by binding to receptors on the cell surface. C. All cell types are able to respond to the same set of signal molecules. D. Each receptor triggers one particular type of cell behavior, for example, activating gene expression. E. Each receptor is generally activated by only one type of signal molecule.

D. Each receptor triggers one particular type of cell behavior, for example, activating gene expression.

Explanation:

Each extracellular signal molecule can induce different responses depending on the target cell. Lipophilic receptors diffuse or carried across the cell's plasma membrane and bind to an intracellular receptor. For example steroid hormones are transported via carrier proteins. Some signalling molecules only induce response from specific cells. A single receptor can be activated by different signal molecules.