Any photosynthesis experts - urgent help needed when testing a green leaf for starch. Any clever clogs?

Hi, I need the answers to the following for a quiz I have entered. All of the contestants are a year above me and therefore, I need some urgent help - its not fair on me!!!





Please help.





The title of this section is "Testing a green leaf for starch."





The questions I am stuck on are:





1. What result would you expect if the plant had been kept in the dark for 48 hours?





2.The ethanol removed the chlorophyll from the leaf. Why was this necessary?





3.Why does the ethanol continue to boil, even though the Bunsen burner is turned off?





Thanks to all who have attempted to answer this question. And oh, remember, the person with the best answer gets 10 points!!!





Good Luck...and Thanks

Any photosynthesis experts - urgent help needed when testing a green leaf for starch. Any clever clogs?
I think I know...so here goes


1 The plant cannot photosynthesise without light so no starch will be produced


2 Chlorophyll is the chemical .(held in chloroplasts) that reacts with light to produce starch. It's what makes green spuds green! I imagine it was removed to eliminate stored starch that would give erroneous readings


3 It has a much lower boiling point than water and will continue to boil because of stored heat in the test tube etc
Reply:1. plants would sort of, scrunch down in on themselves, making their leaves less spread open.. if there is no light to be had, why waste energy holding leaves upright, right?!





2. ethanol is the solvent, will denature the chlorophyll, allowing the chloroplasts to leak out... if left long enough, it will dissolve the chloroplast's membrane... powerful solvent! water wont do it because the chlorophyll is hydrophilic, therefore you need a hydrophobic solvent to denature with. could also use ether.





3. ethanol has a relatively low boiling point, and bunsen burner will heat it up very quickly, so it takes it WAY past it's boiling point temperature wise, so until the glass and metal screen the glassware sits on cools to below ethanol's boiling point, it will continue to boil.
Reply:1. leaves go yellow as chlorophyll not needed. you would find less starch as it needs chlorophyll, starch used to grow pplant upwards tall to reach possible light





2. leaving chlorophyll in makes it possible for some starch to be created. by removing it there is no risk of additional starch being made after putting it in dark and removing





3, confusing statement, but either the mixture being heated reached a temperature above the boiling point of ethanol, so that as it was cooling down without heat input from bunsen it was still above boiling point,. OR maybe a reaction is taking place after heating the mixture that is exothermic and releases enough energy to keep ethanol boiling .





GOOD LUCK



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