Metabolism studies





Abstract
The purpose in experimenting with computer simulations was to compare oxygen consumption rates in different mammalian subclasses. We compared monotremes, marsupials, and placental mammals at both warm and cold temperatures. The results supported our hypothesis that when temperature increased, metabolic rate decreased. This was also supported using a student’s t-test. We also found that placental mammals had the highest oxygen consumption rates and marsupials had the lowest. We compared oxygen consumption rates in different sized crabs at different temperatures. The results supported our hypothesis that the smaller crab would have a higher rate of consumption. However, in the crabs, as temperature was increased, metabolic rate increased also.


Introduction
The second law of thermodynamics affirms that all living organisms must receive a constant energy input in order to survive (Witz 2000). Almost all bodily activities require energy. It is important to study how animals obtain, process, and dispose of products needed to maintain a positive energy balance. When cellular respiration occurs in the body, heat is produced and given off into the environment by the release of potential energy contained in the chemical bonds of macronutrients. The amount of heat released into the environment and the rate at which chemical reactions occur in the cells are directly related. Two different relationships exist, one that describes the endothermic animal and one that describes the endothermic animal. The rate of heat produced by the endothermic animal while at rest, fasting, and within the thermoneutral zone is dependent upon the basal metabolic rate (BMR). The thermoneutral zone of the endotherm is described as the range of ambient temperatures within which there is a limited change in metabolic rate. The standard metabolic rate is what the rate of heat loss in ectotherms relies upon. The difference between the two rates is the 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 exposed to the environment; therefore, it requires more energy to maintain the positive energy balance. Student’s t-tests were used to compare differences in temperature and body size in endotherms and ectotherms, different mammalian subclasses, and in the crab.

Methods
Determining the WMR of endotherms and ectotherms-
In this experiment, we found the average WMRs of a large endotherm, which was a rat, a small endotherm, which was a mouse, and an ectotherm, which was an iguana. The bottom of the metabolism chamber was covered with approximately 50 ml of soda lime, which absorbed any carbon dioxide exhaled by the