Stomatal opening in plants is facilitated by the accumulation of which ion in guard cells?

• A. Potassium Ions
• B. Nitrogen Gas
• C. Iodine Atoms
• D. Sucrose Molecules

Answer: (A)

Opening of stomata hinges on guard-cell turgor, which is driven by the buildup of solutes inside the guard cells. Potassium ions are taken up into guard cells (often with accompanying anions), which lowers the internal water potential. Water then follows by osmosis, the guard cells swell, and the stomatal pore opens. Among the options, potassium ions are the primary driver of this process. The other choices don’t play this role: nitrogen gas is not a solute used by guard cells, iodine atoms aren’t involved in stomatal movement, and while sugars can affect osmotic potential, they do not reliably trigger opening like potassium does.