Metabolism: Effect of Temperature on edno and ectotherms
Animal metabolism consists of the utilization of nutrients absorbed from the digestive tract and their catabolism as fuel for energy or their conversion into substances of the body. Metabolism is a continuous process because the molecules and even most cells of the body have brief lifetimes and are constantly replaced, while tissue as a whole maintains its characteristic structure. This constant rebuilding process without a net change in the amount of a cell constituent is known as dynamic equilibrium (Grolier1996). In the combustion of food, oxygen is used and carbon dioxide is given off. The rate of oxygen consumption indicates the energy expenditure of an organism, or its metabolic rate (Grolier1996).
Metabolic rate is directly linked to the core temperature in an animal. An ectotherm, or cold blooded animal, warms its body mainly by absorbing heat from its surroundings. The amount of heat it derives from its metabolism is negligible. In contrast, endotherms derive most or all of its body heat from its own metabolism (Campbells, p899). Because ectotherms do not produce their own heat, they cannot actively ensure their ideal temperature for an ideal metabolic rate (aquacult. htp).
In the following experiment, we will attempt to examine the relationship between metabolic rate and environmental temperature in both an ectoderm and an endotherm. I predict that for the ectotherm, the metabolic rate will increase as the outside environment temperature will increase. I also predict that the metabolic rate in the endotherm will remain relatively the same as the outside environment temperature changes. I also make the prediction that the ectotherm will have much lower metabolic rates than the endotherm.
The procedures for this experiment are those that are referred to in Duncan and Townsend, 1996 p9-7. In our experiment however, each student group chose a temperature of either 5 C, 10 C, 15 C, or 20 C. Each group selected a crayfish, and placed it in an erlenmeyer flask filled with distilled water. The flask’s O2 levels had already been measured. the flask was then placed in a water bath of the selected temperature for thirty minutes, and then the O2 levels were measured again. Each group shared their findings with the class. The metabolic rates of the mouse were conducted by the instructor and distributed. We also did not use the Winkler method to measure the O2 levels. We used a measuring device instead.
The results of this experiment are shown in the compiled student data in Table 1 below. the metabolic rates of the mouse remained constant with a slight flux, however, the crayfish metabolic rates were very different from one another.
Table 1: Metabolic Rates of Mouse and Crayfish at Various Temperatures Temperature C Metabolic Rate of Mouse (ml O2/min/gm) Metabolic Rate of Crayfish (ml O2/min/gm) 5 0.18 1.04 10 0.19 0.38 15 0.14 0.05 20 0.11 0.26
The regression equations that were calculated for both the mouse and the crayfish were determined through the formula Y = bXi + a. The results were Y = -5.2E-3 X + 0.22 for the mouse, and Y = -0.05 X + 1.1 for the crayfish. To view the procedures for these calculations, view p9-6 in Duncan and Townsend, 1996. Both of these equations have a negative slope, though the slope for the crayfish is substantially larger. The metabolic rates for the crayfish were also higher than the mouse’s metabolic rates.
Based on the results of this experiment, it was shown that as the temperature of the external environment rose, the metabolic rates of both organisms fell. It was also shown that the crayfish had a higher metabolic rate than the mouse. My hypothesis was completely incorrect in stating that the crayfish would have a lower metabolic rate than the mouse. The slope of the crayfish’s linear regression was negative, while I had hypothesized that it would be positive. I was correct in guessing that the endotherm’s metabolic rates would remain steady, which they did with only a slight bit of fluctuation. I believe that there was a significant amount of error in this experiment because many documented facts pertaining to this subject state that the metabolic rate of the crayfish should climb when exposed to higher external temperatures. ‘a warm body temperature contributes to higher levels of metabolic activity’ (Campbells, p899). ‘when ectotherms increase their body temperature using the external environment, their metabolism increases as well’ (Grolier,1996). Both these pieces of
literature state that the metabolism rises as the body temperature rises. My results state that as temperature rises, metabolism drops. Possible reasons for this could be the size of the crayfish used. If each crayfish was a different size, then the larger crayfish would consume more oxygen from the same sized flask than a smaller crayfish might. Therefore, the initial metabolic results could have been from larger specimens than the later results. This could account for the uncharacteristic drop on metabolic rate.
The results that state that the crayfish had a higher metabolic rate than the mouse are also disputed in various pieces of literature. (Campbells, p899) states, ‘an example of energy expenditure at 20 C, a human at rest has a metabolic rate of 1300 to 1800 kcal per day, while a resting ectotherm of the same size like the American Alligator, has a metabolic rate of 60 kcal per day at 20 C’. Ectotherms usually have a much lower metabolic rate than endotherms. I attribute these results to human error. The measurements and calculations may have been done wrong, thus causing the crayfish to appear to have a higher metabolic rate than it really does. Mice are also hibernating creatures, and during the experiment, may have had a lower metabolic rate than usual, because we are currently just coming out of the winter months.
The initial objective to examine the relationship between environmental temperature and metabolic rates was carried out, although the results tabulated may not be reliable enough to consider as legitimate results. Changes in the procedure, such as using the same crayfish for each trial, may have helped to eliminate that one possible source of error. Many more trials could have been done as well, to eliminate human error, or at least make it less likely. The results of the above experiment were not reliable enough to use in stating a definite conclusion.
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