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

How do forests primarily contribute to cooling the air?

1. By shading the ground with large canopies

2. Through the evaporation of water from the forest canopy

3. By blocking sunlight with dense tree cover

4. By producing oxygen during photosynthesis

The correct answer is: Through the evaporation of water from the forest canopy

The primary way forests contribute to cooling the air is through the evaporation of water from the forest canopy. This process, known as transpiration, involves plants taking up water from the soil and releasing it as water vapor through small openings in their leaves. As water vapor transitions from a liquid to a gas, it absorbs heat from the surrounding environment, effectively cooling the air. This not only reduces temperatures but can also contribute to increased humidity, which plays a role in local weather patterns. While shading the ground with large canopies and blocking sunlight with dense tree cover do contribute to a cooler microclimate, these effects are secondary to the cooling provided by evaporation. The production of oxygen during photosynthesis is essential for life and contributes to air quality but does not directly impact air temperature in the same manner as water vapor's cooling effect.