• Sonyalee77
In an experiment, the weight that mice gain is the dependent variable and the temperature of the environment is the independent variable. What must be held constant to obtain valid experimental results? A.the weight of the mice B. the color of the mouse cages C. the length of time that the mice are observed D.the temperature of the laboratory rooms
MIT OCW Biology
  • Stacey Warren - Expert
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  • katieb
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  • Sonyalee77
  • anonymous
I'm not a scientist, as will be obvious by my reasoning. But hopefully by possible mistakes in reasoning, we might all learn something. I think the answer is "c". The experiment will focus the observer on "change in weight with respect to change in temperature". Since it is the difference in weight of a particular mouse we're focusing on, that the mice themselves having a distinct value for an initial weight individually is allowed, as we may still calculate an absolute change in mass. The color of the mouse cages just "seems" wrong to me. Color is a physical property that is useful because it can be subjectively classified, wherein the "field of light" and its distortion by an object with the "property of color" produces a "resultant frequency" very roughly equal to the difference in frequency of incident light and the frequency associated with energy absorbed by the object (the "mechanism" of color). So then the question arises of whether or not the cages themselves may exhibit distinctive mean temperatures (dependent variable) as a function of the constantly held frequency of luminescence. Assuming I were to change the temperature of the laboratory room, there would be an effect (by the assumptions of the question) on the dependent variable. This is axiomatic. As an aside, the nature of this dependency, though, is unknown. Specifically, could such dependency be said to be linear? Or might it be geometric? If I were to take my results and position them honestly on a sheet of paper, appropriately spaced from one another in by Euclid's distance formula in two dimensions, and then "interpolate" or draw a line that satisfies me visually as traveling most "centrally" through the points, would it be straight or would it b curve? What kind of curve might it be? Intuitively, a constant temperature involves a mechanism producing a constant difference (or rate of difference produced) in the dependent variable, but its not a mechanism the experiment is interested in elucidating. We're left with time. I believe time is the one variable that necessarily must stay constant. If we assume time is constant, the temperature change will impart the same energy to each mouse (I assume energy to be the "currency of exchange" producing the final product of weight change), since temperature may be defined as the average kinetic energy of a group of identical molecules (the "air") given by 1/2mv^2. If time is constant, energy imparted is constant for each individual mouse. If temperature is constant, but time is allowed to vary, the transference of energy will be different for each value of time that a mouse is exposed to a constant temperature. Also, by keeping time constant, even variations in temperature will impart equal energy for each mouse.

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