How are cellular respiration and photosynthesis significant similarities and differences?

One of the effects of exercise in a poorly conditioned person is that they produce lactic acid (LA). LA is produced because they cannot supply enough oxygen to oxidize (in the mitochondria) pyruvic acid (PA). PA comes from the anaerobic breakdown of glucose. LA interferes with the enzymatic breakdown of ATP (ATP is the only direct source of energy for cellular function). Thus, the muscles remain tight. 

However, a side effect of LA is it also stimulates the body to grow more capillaries in the lungs and muscles (actually, everywhere) as well as more mitochondria. With more capillaries, more oxygen can get into the blood and muscle cells. Thus, when PA is formed, there are more mitochondria to use the increased amount of oxygen and more energy is released for the rephosphorlation of ADP back into ATP. When this situation exists, more carbon dioxide (co2) and water (h2o) is produced. 

When you exercise, the rate of cellular respiration increases ... that means more co2 is produced. When co2 is mixed with water, it forms an acid, carbonic acid (h2co3). Thus, the bromothyl blue (BTB) turned yellow. The better shape you're in, the more co2 you'll produce and the more h2co3 will be made immediately after exercising and the BTB will change more quickly. 

If you're in good shape, the rate of co2 will peak and drop off quickly. If you're in poor shape, the rate of co2 will rise some and stay increased for a longer period of time. 

Carbon dioxide is the correct answer