Name: ______________________________
PhotosynthesisInvestigation1
Part1.MeasuringtheRateofPhotosynthesis
Youwillusethe"floatingleafdisk"methodtomeasuretherateofphotosynthesis.Tobegin,cutseveral
disksfromaspinachleafandputtheseleafdisksinacupofwater.
1.Doyourleafdisksfloat?
Usetheinformationinthisdiagramofa
cross-sectionofaleaftoexplainwhya
leafdiskwouldfloat.
Thewhiteovalinthecenterofeachcellrepresentsavacuole
whichisfilledwithwaterwithdissolvedsubstances.Thedark
spotsinthemesophyllcellsrepresentchloroplasts.
2.Wheredoesphotosynthesisoccurinaleaf?Statewhichorganellescarryoutphotosynthesisandwhich
typeortypesofleafcellshavethisorganelle.
3.Explainwhyitisusefultotheplanttohaveairspacesaroundthespongymesophyllcellsintheleaves.
(Hint:Recallthechemicalequationforphotosynthesis: light
6CO2+6H2OC6H12O6+6O2)
1Adapted
from Investigation 5 in College Board Teacher Manual for AP Biology Investigative Labs,
http://www.collegeboard.com/html/apcourseaudit/courses/pdfs/cb-biology-lab-manual-1-24-12.pdf by Drs. Ingrid Waldron, Linda Robinson and Scott Poethig,
Department of Biology, University of Pennsylvania, © 2016. This Student Handout and Teacher Preparation Notes with instructional suggestions and background
information are available at http://serendip.brynmawr.edu/sci_edu/waldron/#photosynthesis.
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4.Tomeasuretherateofphotosynthesis,youwillreplacetheairinthespongymesophyllinyourleaf
diskswithaliquid.Thiswillcausetheleafdiskstosink.Thenyouwillputtheseleafdisksinwaterwith
dissolvedCO2andmeasuretheamountoftimeittakesfortheleafdiskstofloat.Whichproductof
photosynthesiswillaccumulateinthespongymesophyllandcausetheleafdiskstofloat?
Forphotosynthesistooccurintheleafdisksthathavehadtheairsuckedout,youwillnedtoprovidethe
leafdiskswithlightandagoodsourceofCO2dissolvedinwater.Forthispurpose,youwilluseasolution
ofsodiumbicarbonate(NaHCO3)inwater.Sodiumbicarbonatereactswithwaterasfollows:
NaHCO3+H2ONaOH+H2CO3NaOH+H2O+CO2
5.Asacontrol,youwillputsomeleafdisksinwater(withnosodiumbicarbonate).Doyouexpectthese
leafdiskstofloat?___yes___no
Explainyourreasoning.
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Spinach Disc Lab Answer Sheet
PRE-LAB
Research Question: What do you want to know?
Independent variable: what experimental factor will you change to produce an outcome?
Dependent variable: what will you measure? Will you collect quantitative data or qualitative
data?
Control group: what kind of control group will you establish as a standard for comparison?
Constants: what conditions will you keep constant? Name at least 3.
DURING LAB
Results:
Number of Spinach Disks Floating
Time (minutes)
0
1
2
3
4
5
6
In Water
Bicarbonate
solution
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7
8
9
10
11
12
13
14
15
POST-LAB: graph your group’s data and the class average.
Graph: ________________________________________________________________________
Conclusion: Answer in complete sentences!
1. What gas is being consumed in photosynthesis? What gas is being produced in
photosynthesis?
2. How do the gasses consumed and produced in photosynthesis affect the buoyancy of the
leaf?
3. Possible errors:
o
What possible errors may have affected the results? (Identify at least one.)
o
How would the results be different had these errors not occurred?
4. Think about other variables that may affect the rate of photosynthesis. Choose ONE
variable and describe how you would set up an experiment to test it.
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