The rate of oxygen output remains constant between points P and O because A - VCE - SSCE Biology - Question 14 - 2017 - Paper 1

To answer this part of the question, we recognize that photosynthesis is dependent on several factors including light intensity, temperature, and the availability of carbon dioxide. When the concentration of carbon dioxide is limited, photosynthesis cannot proceed at a faster rate, regardless of other conditions. Therefore, it is logical that the rate of oxygen output would remain constant, as there is insufficient carbon dioxide available to increase the rate of photosynthesis, leading to a stable oxygen output between points P and O.