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Paracrine ligand molecules are normally degraded by enzymes or removed by neighboring cells soon after release. What does this rapid removal accomplish for the signal?
AIt keeps the response localized by reestablishing the concentration gradient
BIt converts the paracrine ligand into a long-lasting hormone
CIt moves the ligand into the bloodstream for wider distribution
DIt allows the ligand to bind cell-surface receptors on distant organs
Answer & Solution
Correct answer: A. It keeps the response localized by reestablishing the concentration gradient
1. Paracrine ligands are quickly degraded by enzymes or removed by neighboring cells after release.
2. Removing the ligand reestablishes the concentration gradient, allowing quick diffusion again if the signal is released a second time.
3. This rapid clearance keeps the paracrine response localized and short lived, unlike endocrine signaling.
4. Turning a paracrine ligand into a hormone or sending it into the bloodstream would spread the signal rather than keep it local, which contradicts the described purpose.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section 9.1 Signaling Molecules and Cellular Receptors_
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