A scientist studying the oxidation of fatty acids in extract of liver found that when palmitate (16:0) was provided as substrate, it was completely oxidized to CO2. However, when undecanoid (11:0) was added as substrate, incomplete oxidation occurred unless he bubbled CO2 through the mixture. The addition of the protein avidin prevented the complete oxidation of 11:0 even in the presence of CO2, although it had no effect on 16:0 oxidation. Explain these observations.