TeXes Science Practice Test

Which of the following correctly describes the role of guard cells in plants?

1. They absorb nutrients for the plant

2. They control the opening and closing of stomata

3. They transport water throughout the plant

4. They store energy in the form of starch

The correct answer is: They control the opening and closing of stomata

Guard cells play a crucial role in the regulation of gas exchange in plants by controlling the opening and closing of stomata. These specialized cells are located on either side of a stoma, the small openings found on the surface of leaves. When guard cells absorb water and become turgid, they bend away from each other, causing the stomatal pore to open. This allows essential gases, such as carbon dioxide to enter for photosynthesis, and oxygen to exit. Conversely, when guard cells lose water, they become flaccid and close the stomata, which helps prevent excessive water loss through transpiration and can also protect the plant from drought conditions. Understanding this functioning of guard cells is vital for grasping how plants maintain homeostasis and respond to environmental changes. The other options do not accurately depict the role of guard cells. While absorbing nutrients and transporting water are essential functions in plants, they are typically carried out by roots and vascular tissues. Storing energy in the form of starch is primarily a function of various plant tissues, particularly parenchyma cells, and is not related to the function of guard cells.