BIOL373L Lecture Notes - Lecture 5: Pipette, Asthma, Indirect Calorimetry
5 May 2018
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Determining the Metabolic Rate of a Laboratory Mouse Based on Oxygen Consumption
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Introduction
The purpose of this experiment was to determine the metabolic rate of a mouse by
observing, measuring and analyzing its oxygen consumption. Metabolic rate can be defined as
the rate at which fuels are broken down to keep cells functioning efficiently in a living organism
(Khan, 2018). The lowest possible metabolic rate in an individual or the metabolic rate of an
individual at rest is termed the basal metabolic rate (BMR) (Silverthorn, 2013). Metabolic rate
can be measured and expressed in units such as calories or joules per unit of time or by the
amount of carbon dioxide produced (or oxygen consumed) per unit time (Khan, 2018).
Metabolic rate will vary among different organisms and will also depend on the activity level of
the organism (Khan, 2018). For instance, a more active organism will have a higher metabolic
rate than a less active organism (Khan, 2018). There are several other factors that influence an
organisms metabolic rate. Factors specific to humans include age, sex, lean muscle mass, size,
diet, hormones, and genetics (Silverthorn, 2013). For instance, females tend to have a slightly
lower BMR than males and individuals with a higher lean muscle mass will consume more
oxygen per unit time (Silverthorn, 2013). Similarly, younger individuals will have a higher
oxygen consumption rate (and ultimately a higher metabolic rate) than older individuals
(Silverthorn, 2013).
As obligate aerobic mammals, we are heavily dependent on oxygen to drive cellular
processes, chemical reactions, and maintain an overall good health. Oxygen consumption is
defined as the rate at which the body consumes oxygen as it metabolizes nutrients (Silverthorn,
2013). Once metabolized, oxygen becomes the basic fuel source for our cells (Cichorski, 2008).
On a macro scale, oxygen is metabolized and used in the contraction of muscles, a key process
that allows us to perform the most basic of functions (Cichorski, 2008). Its stands to reason, then,
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that because our bodies are so heavily dependent on oxygen, an organisms level of its
consumption is a perfect indicator of that organisms’ metabolic rate (Cichorski, 2008).
Using the mouse’s oxygen consumption in this matter is a form of indirect calorimetry
(Silverthorn, 2013). To use oxygen consumption as an indicator of metabolic rate, we first must
assume that the volume of oxygen used by the mouse is equal to the volume of carbon dioxide
produced (Silverthorn, 2013). For a large mammal like a human, this is not an ideal assumption
because the amount of oxygen an organism inhales is not equal to the amount of carbon dioxide
that is exhaled (Hoong et al., 2008). On average, of the amount of air inhaled approximately 21%
of it is oxygen and of the amount of air exhaled, 4% is carbon dioxide (Hoong et al., 2008). The
animal used in this experiment, however, is small enough that the difference in oxygen
consumption and carbon dioxide production is negligible and will not significantly affect the
results (Ehrlich, 2016). Additionally, the carbon dioxide produced by the mouse will be absorbed
by soda lime lining the base of the chamber (Toole & Toole, 2004). This will cause an overall
decrease in the amount of air in the chamber and hence infer the oxygen consumption indirectly
(Toole & Toole, 2004).
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Document Summary
Determining the metabolic rate of a laboratory mouse based on oxygen consumption. The purpose of this experiment was to determine the metabolic rate of a mouse by observing, measuring and analyzing its oxygen consumption. Metabolic rate can be defined as the rate at which fuels are broken down to keep cells functioning efficiently in a living organism (khan, 2018). The lowest possible metabolic rate in an individual or the metabolic rate of an individual at rest is termed the basal metabolic rate (bmr) (silverthorn, 2013). Metabolic rate can be measured and expressed in units such as calories or joules per unit of time or by the amount of carbon dioxide produced (or oxygen consumed) per unit time (khan, 2018). Metabolic rate will vary among different organisms and will also depend on the activity level of the organism (khan, 2018). For instance, a more active organism will have a higher metabolic rate than a less active organism (khan, 2018).
