What characteristic distinguishes autocrine signals from paracrine signals?

Autocrine signals are distinguished by their ability to affect the cell that secretes them. This means that when a cell releases a signaling molecule, it can bind to receptors on its own surface, leading to a response within the same cell. This self-targeting is crucial in various biological processes, such as immune responses, where a cell might amplify its own activity in response to an external signal or during developmental processes to regulate growth and differentiation.

In contrast, paracrine signals act on nearby neighboring cells rather than the secreting cell itself. They tend to have a limited range, affecting only cells within a short distance. The remaining options describe general characteristics of signaling mechanisms or are not specific enough to distinguish between these two types of signaling. For instance, signaling does require receptors on cell surfaces, but this is true for both autocrine and paracrine signals, making it an irrelevant point for differentiation.