Biology Experiment Question Watch

WillHippo
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Hi there,

I am confused about the variables in a specific Biology experiment. I am investigating what affect Surface Area to Volume ratio has on the rate of diffusion.

The method involves taking multiple agar cubes (dyed with phenolphthalein) of different widths and putting them in a Sodium Hydroxide solution for 5 minutes. After the 5 minutes are up, the cubes are removed (and blotted on paper towels to remove excess NaOH). At this point, the agar on the outside of the cubes should be clear as the NaOH solution will have diffused into it and removed the dye, but depending on the volume of the cube, there should be a cube of still dyed agar in the centre that the NaOH hasn't reached yet. By cutting the cube in half, I will be able to measure the width of this 'undiffused' cube, which I can then cube, to find the volume of it, and then subtract from the total volume of the cube. This should give the volume of agar that has been diffused into by the solution.

I will take this value and then divide by the total volume of the agar cube, to give the % of the cube that has been diffused into. However, my question is this: what is the dependent variable? I will plot the % cube dissolved into on the y axis of my graph, although I will be physically measuring the width of the 'undiffused' cube in the centre of the agar cube.

Thanks to anyone who has read this far, and who has an answer.
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Joe0123456789
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The independent variable is the percentage diffused, and the dependent variable is the surface area to volume ratio. Hope this helps.
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madele
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The dependent variable would just be the amount of diffusion that you measure in the agar.

The independent variable would be the different sizes of the agar cubes.
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WillHippo
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(Original post by madele)
The dependent variable would just be the amount of diffusion that you measure in the agar.

The independent variable would be the different sizes of the agar cubes.
Thanks for answering madele. By "the amount of diffusion that you measure in the agar" do you mean the volume of the agar that the solution has diffused into or the percentage that this has happened to?

Joe0123456789, I think you've written the variables the wrong way round.

Thanks for the help.
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madele
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(Original post by WillHippo)
Thanks for answering madele. By "the amount of diffusion that you measure in the agar" do you mean the volume of the agar that the solution has diffused into or the percentage that this has happened to?

Joe0123456789, I think you've written the variables the wrong way round.

Thanks for the help.
Edit as I read your question wrong - doh!

A percentage would be a better choice when you are using cubes of variable volumes.
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houh
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hAHAHAHAHAHAH YUR ALL FOKKEN WRONG BOYZZZZ
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