Final answer:
Active transport is the process that directly affects turgor pressure in guard cells, causing stomata to open or close by regulating ion movement and water flow, which is integral for photosynthesis and transpiration in plants. The correct option is B. Active transport
Step-by-step explanation:
The process that contributes directly to the turgor pressure that opens and closes stomata is B. active transport. During active transport, ions such as potassium (K+) are pumped into the guard cells, which increases the osmotic pressure inside these cells, leading to water influx and subsequent cell swelling. This swelling causes the stomata to open.
Conversely, when potassium ions are pumped out of the guard cells, the water follows due to osmotic gradients, leading to a decrease in turgor pressure, resulting in the stomata closing. It is through this mechanism that plants regulate gas exchange and water loss through transpiration, adapting their photosynthesis and water retention to environmental conditions.
Several environmental conditions can cause stomata to close, including water deficit, darkness, and the presence of certain gases like ozone or sulfur dioxide. During the day, high light levels and lower intracellular carbon dioxide concentrations typically trigger the opening of stomata to allow for photosynthesis and transpiration.
It is important to note that while transpiration is a passive process driven by water vapor differences between the plant and the atmosphere, the control of stomatal opening and closing by guard cells is an active, energy-dependent process. The correct option is B. Active transport