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

Where does water primarily escape from in plants during transpiration?

1. Through the root system

2. Through the stomata

3. Through the xylem vessels

4. Through the leaves' epidermis

The correct answer is: Through the stomata

Water primarily escapes from plants during transpiration through small openings on the surfaces of leaves known as stomata. Stomata are surrounded by guard cells that regulate their opening and closing, allowing for the exchange of gases (such as oxygen and carbon dioxide) as well as the release of water vapor. Transpiration is an essential physiological process that helps maintain a continuous flow of water from the roots through the plant and into the atmosphere. This not only supports photosynthesis by providing water for the leaves but also aids in nutrient uptake from the soil and helps regulate temperature within the plant. While the root system, xylem vessels, and the epidermis of the leaves also play roles in water's movement and retention, they are not the primary sites of water loss. The root system is involved in water absorption, the xylem transports water throughout the plant, and although some water may escape through the leaves’ epidermis, the majority of transpiration occurs through the stomata. This makes stomata the key site for effective water loss during transpiration in plants.