Certified Crop Advisor Practice Exam

Which element regulates stomatal openings in plants?

1. Calcium

2. Carbon

3. Potassium

4. Nitrogen

The correct answer is: Potassium

Stomatal openings in plants are primarily regulated by potassium ions. When environmental conditions signal the need for gas exchange, such as uptake of carbon dioxide for photosynthesis or transpiration for cooling, potassium plays a crucial role in this process. Specifically, potassium ions are actively transported into the guard cells of the stomata. As potassium enters these cells, it causes an osmotic movement of water into the guard cells, leading to their turgidity. This increase in turgor pressure results in the opening of the stomata, allowing for gas exchange. Conversely, when potassium ions are removed from the guard cells, water follows out, causing the cells to become flaccid, and the stomata close. Other elements such as calcium, carbon, and nitrogen have their distinct roles in plant physiology but are not directly responsible for the regulation of stomatal openings. Calcium, for instance, is involved in signaling pathways and structural functions of cells, while carbon is primarily related to photosynthesis, and nitrogen is essential for protein synthesis and overall growth. However, it is potassium that specifically drives the mechanisms controlling the opening and closing of stomatal pores.