temperature factor. Due to that fact that the temperature of ectotherms has a wider range with ambient temperature than the endotherms, physiologists defined a different measure for the basal level of metabolism. Although it is possible to measure the animal’s heat lost to the environment by direct calorimetry, it is easier to use indirect calorimetry. An effective way of measuring heat loss is to use the rate of oxygen consumption. Since oxygen is required by most animal cells using biochemical pathways to metabolize macronutrients, and it varies in a predictable way, it is useful in determining metabolic rate. If we can estimate BMR accurately, we can predict the amount of energy needed for important aspects of the animal’s life, such as growth and reproduction. For comparative purposes in the laboratory, we will be comparing weight-specific metabolic rates. This will allow us to compare the oxygen used by a gram of rat tissue to the oxygen used by a gram of mouse or iguana tissue. We hypothesized that the metabolic rate of the ectotherms, which are the iguanas, will be lower than the metabolic rate of the endotherms, which are the rats and the mice. Computer simulated temperature differences in the environment of both endotherms and ectotherms will also cause a difference in metabolic rate. When exposed to cold temperatures, we hypothesized that the metabolic rate will be greater than when the organism is exposed to high temperatures. The animal requires a greater amount of energy to keep the body warm at low temperatures; therefore, the body must breakdown the macronutrients at a faster rate. Body size also influences metabolic rate. A smaller animal, such as a mouse, should have a greater metabolic rate than a larger animal with the same general morphology, like a rat. This difference in metabolic rate is due to the surface area to volume ratio. A smaller animal has a higher ratio and more surface area ex...
