Which of the following statements is true? Both respiration and photosynthesis consume carbon dioxide. Respiration consumes carbon dioxide, whereas photosynthesis produces it. Respiration produces carbon dioxide, whereas photosynthesis consumes it. Both respiration and photosynthesis produce carbon dioxide. Question 4 The Keeling curve shows that despite seasonal fluctuations, CO2 levels are roughly constant reveals both annual and long-term changes in CO2 levels illustrates how there is more photosynthesis happening in Hawail shows how, on a global scale, photosynthesis occurs at a constant rate.