Final answer:
Stomata open during the day in response to blue light, which signals the uptake of potassium ions (K+) by guard cells, resulting in their swelling and the opening of stomata for gas exchange needed for photosynthesis.
Step-by-step explanation:
Stomata open during the day in response to blue light triggering the uptake of K+ by guard cells.
Stomata are pores found mainly on the underside of leaves, and they regulate gas exchange by opening and closing. The process is controlled by guard cells, which swell or shrink based on the osmotic balance, thus altering the opening of the stomatal pore. Environmental factors like light and carbon dioxide levels heavily influence stomatal movements. When the blue light is present, it acts as a signal that promotes the uptake of potassium ions (K+) by the guard cells. This uptake of ions causes water to flow into the cells due to osmotic pressure, making the guard cells turgid and opening the stomata. This activity is crucial for photosynthesis to proceed during the day, as open stomata allow CO2 to enter the leaf for the photosynthetic process. By contrast, factors such as the production of abscisic acid (ABA), a plant stress hormone, typically signal the guard cells to release K+, leading to the loss of turgor and closure of stomata, which helps reduce water loss during stressful conditions like drought.