The Hill Reaction Lab help?Why were all samples placed exactly 15 cm from the light source and exposed to light from the floodlight for 2 min all at the same time? In your answer explain why...

The Hill Reaction Lab help?

Why were all samples placed exactly 15 cm from the light source and exposed to light from the floodlight for 2 min all at the same time? In your answer explain why cuvette 5 (wrapped in aluminum foil) was also exposed to the light aong with the other four cuvettes?

Here is the procedure and data collected from the lab.

http://bayviewss.ca/halk/halk/Biology_12_files/Hill%20Reaction%20wksht.pdf

Help is greatly appreciated, thanks!

Asked on by sj-14

1 Answer | Add Yours

bandmanjoe's profile pic

bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

Posted on

What you are describing here is a control variable.  The whole point of this lab is that light is going to initate the electron transport chain that normally takes place while photosynthesis is going on in the chloroplasts.  We want to control all the other variables, such as distance to the light source and the amount of time the cuvettes were exposed to the light.  In other words, we are testing to see if the light exposure makes a difference in activation of the electron transport chain.  If we don't control the other variables, how can we be sure that was the factor that affected it?  You only test one variable at a time; all the other ones are controlled, so they are not a factor to be considered.

The cuvette that was covered in aluminum foil obviously would not permit the light to enter the chloroplasts.  So we would expect to see little, if any, color change from the indicator, it should still be a blue color, indicating it had not been reduced by the addition of electrons from the electron transport chain.  This cuvette would be the experimental variable; you allowed light to radiate through the other four cuvettes, but this fifth one, you did not.  We think whether light is present or not makes the difference.

Sources:

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