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

Which process is primarily affected by the opening and closing of stomata?

1. Photosynthesis

2. Cellular respiration

3. Transpiration

4. Growth

The correct answer is: Transpiration

The process that is primarily affected by the opening and closing of stomata is transpiration. Stomata are small openings on the surfaces of leaves that can open and close to regulate gas exchange and water loss. When stomata are open, water vapor can escape from the inside of the leaf into the atmosphere, a process known as transpiration. This loss of water creates a negative pressure that helps draw water and nutrients up from the roots through the plant's vascular system. Transpiration is closely linked to the plant's ability to maintain its water balance and temperature, and it plays a role in nutrient transport. The opening of stomata also allows for the intake of carbon dioxide, which is crucial for photosynthesis, but in this context, the primary function of stomata relates to the regulation of water loss through transpiration. Photosynthesis is indeed affected by stomatal opening, as it requires carbon dioxide; however, the main focus of the question is on transpiration, which is directly influenced by how stomata function. Cellular respiration and growth are processes that take place throughout the plant and are not directly linked to the immediate function of stomata.