But red blood cells don't have organelles, they don't have any mitochondria. And what that means is they don't have the cell machinery needed for aerobic respiration. So red blood cells only use anaerobic cellular respiration to produce ATP molecules. And so red blood cells produce many of these lactate molecules. So once again, lactate is the major precursor molecule that can be used to form glucose. In gluconeogenesis, skeleton muscle cells produce lactic acid which then dissociates into lactate and the H plus ions during exercise when the rate of glycolysis is greater than the rate of oxidative aspirulation that takes place in the mitochondria.