bio homework

snnys1
timer Asked: Apr 15th, 2016

Question Description

just do the two drew 

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Experiment 3: Effect of Molecular Weight on Diffusion In the third column of the following table, record the diameters of the dye spots after 60 min- utes of diffusion. Then calculate (D - 4)/2, where D is the diameter of the dye spot in mm and 4 is the diameter of the hole in the agar. This calculated value is the distance that the dye has moved in any direction from the edge of the hole. Record these values in the fourth column of the table and plot the data on the graph below. Table 5-3. Dye Molecular Weight Diameter at 60 min. (D) Distance Migrated (D-4)/2 3 Reactive red 1470 mm Methyl green 653 5.5 10 15 0.9cm 10,7cm Amido black 616 9 9mm 7mm 2.5 Xylene cyanol 555 1.5 Molecular Weight vs. Distance 1500 1400 1300 1200 1100 1000 Molecular weight 900 800 700 600 500+ 0 1 5 6 2 3 4 Distance migrated (mm) Diffusion rates have the general tendency to decrease as molecular weights increase. However, the relationship between molecular weight and the rate of diffusion for these dyes is not linear. Instead, their diffusion rates decrease exponentially as their molecular weights increase. In a case like this, it is useful to mathematically transform the data so that a relationship between variables can be made into a linear one. Using the common logarithms of the molecular weights transforms the exponential relationship into a linear one. You can calculate the common logarithms of the molecular weights of each of the four dyes and graph these against distance migrated on standard graph paper. However, there is a simpler method of transforming data that show exponential relationships. Semilog graph paper consists of a horizontal axis that is in a linear scale and a vertical axis that is in a logarithmic scale. Plotting molecular weights on the logarithmic scale has the effect of taking their logarithms without performing any calculations. Plot the actual molecular weights versus diffusion distances on the following semilog graph. The axes of this graph have been partially labeled to facilitate this process. (You must label the x-axis to accommodate the migration distances that you measured.) Molecular Weight vs. Distance 10,000 9000 8000 7000 6000 5000 4000 3000 2000 Molecular weight 1000 900 800 700 600 500 400 300 200 100 2 3 4 5 6 7 8 9 10 Distance migrated (mm) Just like the distance between two cities, which can be expressed in terms of absolute miles, travel hours by car, ticket fare by plane, etc., there are many equivalent ways to express bio- logical variables. The preferred way to express variables is whatever way results in the clearest visualization of the relationship between the variables. In the present example, transforming molecular weights into their common logs had the effect of generating a linear relationship that is the easiest type of relationship to interpret graphically.
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