Which statement describes how hormones exert their effects on distant targets?

Which statement describes how hormones exert their effects on distant targets?

• A. Hormones alter cellular activity by binding receptors
• B. Electrical impulses trigger rapid muscle contraction
• C. Hormones are destroyed before reaching targets
• D. Direct transfer of DNA to target cells

Answer: (A)

Hormones exert effects on distant targets by traveling through the bloodstream and binding to receptors on or in those target cells. This receptor binding starts signaling processes inside the cell—either by activating second messenger systems or by changing gene transcription—ultimately altering the cell’s activity. The location and type of receptor determine the exact response: peptide and protein hormones bind to cell-surface receptors to trigger quick signaling cascades, while steroid hormones cross the membrane and interact with intracellular receptors to influence gene expression. The other statements don’t fit because electrical impulses describe nervous-system signaling rather than endocrine signaling, hormones aren’t simply destroyed before reaching targets (they are carried to them via the blood and only affect cells with the appropriate receptors), and hormones don’t directly transfer DNA to target cells.

Hormones exert effects on distant targets by traveling through the bloodstream and binding to receptors on or in those target cells. This receptor binding starts signaling processes inside the cell—either by activating second messenger systems or by changing gene transcription—ultimately altering the cell’s activity. The location and type of receptor determine the exact response: peptide and protein hormones bind to cell-surface receptors to trigger quick signaling cascades, while steroid hormones cross the membrane and interact with intracellular receptors to influence gene expression. The other statements don’t fit because electrical impulses describe nervous-system signaling rather than endocrine signaling, hormones aren’t simply destroyed before reaching targets (they are carried to them via the blood and only affect cells with the appropriate receptors), and hormones don’t directly transfer DNA to target cells.