ISA Certified Arborist Practice Exam 2026 – All-in-One Resource for Comprehensive Exam Success!

Sunlight is essential for photosynthesis to occur in leaves because it provides the energy needed for the process to take place. Humidity and temperature can affect the rate of photosynthesis, but they are not essential for it to occur. Regular watering is important for plant health, but it is not directly related to photosynthesis. Without access to sunlight, leaves cannot carry out photosynthesis and produce food for the plant. Therefore, access to sunlight is the most essential quality for photosynthesis to occur in leaves.