# Question regarding Rate of Photosynthesis AP Biology Lab

We are doing a lab on the effects of light intensity/wavelength on the rate of photosynthesis in AP bio and we were asked to visit this website here: http://mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm

The link takes you to a shockwave applet in which you can change the wavelength/intensity and record the ATP production (%). We were supposed to try out as many different combinations of intensity/wavelength and record the respective intensity, wavelength and ATP production (%) in a chart. Now the problem I'm having is that we are to graph this data. How should I go about graphing this? One problem is that for some values in the data, the intensity might be the same with different wavelengths or the wavelength maybe the same with different intensities. Can I do two graphs? One graph? Which one would be best and how should I go about doing so? And here is the chart just in case you want to see the data:

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Why ecology tag? Come to think about it, why energy tag? To be completely honest with you, it is not strictly a photosynthesis question either, and I think you could have asked this question on stats SE or math SE too, because the question is "how to plot?" rather than about photosynthesis. Personally, I still think it's an okay question to ask on biology SE, but maybe we should edit the tags a little. Anyway, I'm happy to help you to the best of my ability, welcome to biology SE :-) – Th334 Jan 14 '14 at 11:07
Ty for the welcome and I have not posted this question on any other stackexchange sites. And yes I agree that the question really is about graphing but still the graphing is directly related to biology and so I thought it would be reasonable to post this here. Also I couldn't find any other related tags; these were the ones that came closest to the question =S. – genius12 Jan 14 '14 at 22:17

Your task is to determine how light intensity and wavelength affect ATP production. Therefore, we know for sure that your dependent variable (or response variable) should be ATP production. It is customary to depict the response variable on the vertical axis (Y-axis), so let's trying doing this.

Now we need to sort the other two variables. I suggest that you make one variable a control variable -- a variable that you don't change and keep constant, and the other then will be an independent variable (or explanatory variable). Then you swap them around, producing at least two plots.

In a nutshell:

1. You pick one value of wavelength and don't change it. Then you change the light intensity and record ATP with constant wavelength. You plot ATP (vertical axis) vs the light intensity (horizontal axis).

2. You pick one value of light intensity and don't change it. Then you change the wavelength and record ATP with constant light intensity. You plot ATP (vertical axis) vs the wavelength (horizontal axis).

Make sure to generate enough data points in order to be able to fit a smooth curve.

Another option would be to make a 3-D graph, with 3 axes: Y for ATP, X for wavelength and Z for light intensity. Initially, this might seem like a better approach, however 3-D graphs are not very common in science, and maybe there is a reason for it. Your goal is to make your data intuitive, easy to read and straight to the point. Science can be rather complex even without additional effort to complicate it with confusing graphs.

I would try it out as well, and see which one of two approaches shows you the trend more clearly. If I had to pick one straightaway -- I would probably go with the previous option that included a control variable.

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This is a great idea and this is how I initially thought I should do it but I actually ended up doing it differently and handed the lab in today =] – genius12 Jan 14 '14 at 22:18
@genius12, did I overlook a better solution? Do you mind sharing it? Good luck with you report. – Th334 Jan 14 '14 at 23:20