A previously unknown chemical signal is discovered in mice. Five observations about this signal are listed. Which observation would serve as evidence in distinguishing whether this chemical signal should be classified as a juxtacrine or a paracrine signal?

The signal molecule is not present in extracellular fluid

Explanation:

In paracrine signaling, the signaling molecules released by a cell only affect target cells in close proximity to it though it does not require the direct contact of the cells involved. the conduction of an electric impulse from one nerve cell to another or from a nerve cell to a muscle cell occurs via paracrine signaling. In juxtacrine signaling, physical contact between the two cells involved is required and it occurs between neighboring cells that have extensive patches of closely opposed plasma membranes linked by transmembrane channels known as connexons. There is the presence of signal molecules in extracellular fluids in juxtacrine signaling unlike paracrine signaling.

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