OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is the role of the inner and outer walls of guard cells?

1. They protect the leaf from pests

2. They store nutrients

3. They assist in the opening and closing of stomata

4. They facilitate photosynthesis

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

The inner and outer walls of guard cells play a crucial role in the regulation of stomata, which are small openings on the leaf surface. These guard cells are specialized cells that control the size of the stomatal pore. When the plant needs to take in carbon dioxide for photosynthesis, the guard cells swell by absorbing water, causing them to bend and open the stomata. Conversely, when water needs to be conserved, the guard cells lose water, causing them to become flaccid and close the stomatal openings. This dynamic movement directly influences gas exchange, allowing the plant to regulate the intake of carbon dioxide and the release of oxygen and water vapor. The other options, while relevant to plant functions, do not accurately describe the specific role of guard cells. Protecting the leaf from pests relates more to physical structures like trichomes or chemical defenses, nutrient storage is associated with other cell types in plants (like parenchyma), and while stomatal function is related to photosynthesis, the primary direct function of guard cells is indeed the opening and closing of stomata. Thus, the correct answer highlights their essential role in facilitating gas exchange and maintaining homeostasis within the plant.