Certified Crop Advisor Practice Exam

Stomates regulate water losses from leaves by varying the ________ to water vapor movement from the leaf to the atmosphere.

1. flow rate

2. resistance to

3. amount of sunlight

4. pressure

The correct answer is: resistance to

Stomates, or stomata, are small openings on the surface of leaves that play a crucial role in regulating gas exchange and water loss. They control the resistance to water vapor movement from the leaf to the atmosphere by changing their aperture, or how wide they open or close. When stomata are open, there is less resistance and water vapor can easily diffuse out of the leaf into the air. Conversely, when stomata close, resistance increases, which significantly reduces water loss. Effective regulation of this resistance allows plants to maintain moisture levels while still enabling necessary gas exchanges for photosynthesis. In dry conditions, stomata may close to conserve water, but in favorable conditions, they will open to facilitate transpiration, which helps in nutrient transport and cooling the plant. The other options, while relevant to plant physiology, do not directly relate to the primary function of stomates in this context. Flow rate pertains to quantity rather than resistance. The amount of sunlight influences photosynthesis but does not directly regulate water vapor movement. Pressure could relate to how gas exchanges occur but is not a mechanism by which stomates control water loss.