Questions: What is endocrine signaling? A type of signaling that involves the release of hormones into the bloodstream When a signal molecule is released into the bloodstream to reach distant target cells A type of signaling where the signal molecule acts on cells in a different tissue A type of signaling where the signal molecule acts on the same cell that released it A type of signaling that occurs between adjacent cells

The answer is the first one: A type of signaling that involves the release of hormones into the bloodstream.

Explanation for each option:

1. A type of signaling that involves the release of hormones into the bloodstream: This is the correct definition of endocrine signaling. In endocrine signaling, hormones are released by endocrine glands into the bloodstream, which then travel to distant target cells to exert their effects.

2. When a signal molecule is released into the bloodstream to reach distant target cells: This is also a correct description of endocrine signaling, but it is not as precise as the first option. It describes the process but does not explicitly mention hormones.

3. A type of signaling where the signal molecule acts on cells in a different tissue: This describes paracrine signaling, where the signal molecule affects nearby cells in different tissues, but not necessarily through the bloodstream.

4. A type of signaling where the signal molecule acts on the same cell that released it: This describes autocrine signaling, where the signal molecule affects the same cell that released it.

5. A type of signaling that occurs between adjacent cells: This describes juxtacrine signaling, where the signal molecule affects adjacent cells through direct contact.

Summary: Endocrine signaling involves the release of hormones into the bloodstream to reach and act on distant target cells. The correct answer is the first one.