TeXes Science Practice Test

Stomatal closing in plants is a response to what kind of environmental stress?

1. Cold, wet weather

2. Hot, dry weather

3. High humidity

4. Extreme wind

The correct answer is: Hot, dry weather

Stomatal closing is a crucial physiological response in plants to conserve water, particularly during hot and dry weather conditions. When temperatures rise and soil moisture diminishes, plants experience stress due to the increased rate of transpiration—where water vapor is lost from their leaves. To mitigate this loss and maintain internal water balance, plants respond by closing their stomata, which are small openings on the leaf surface that facilitate gas exchange. By reducing the size of these openings, stomatal closing effectively minimizes water loss while also limiting the intake of carbon dioxide for photosynthesis. This adaptation is vital for survival during periods of drought, enabling plants to endure adverse conditions until better moisture levels return. In contrast, the other options—cold, wet weather; high humidity; and extreme wind—do not typically induce stomatal closure as a primary response. In cold and wet conditions, for instance, plants may continue to transpire normally, as water loss is less of a concern. High humidity often decreases transpiration rates naturally, relieving stress rather than necessitating stomatal closure. Likewise, extreme wind does not directly create the same level of water stress that heat and dryness do, so it would not typically trigger this specific response.