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StudentGuide
AP' Biology Laboratory 5
Cell Respiration
Objectives
.
Measurethe consumptionof oxygenby respiring
seeds
.
Comparerespirationratesat two different temperatures
Background
Many cellularprocesses
requireenergy.Aerobic cellularrespirationsupplies
energyby the oxidation of
glucose'This is a complexprocessinvolving
a number of
reactions;however,we can
summarizethe processin termsof input
".ry-.--ediated
output produ.tr'riil-,
n ,r"ry simpleequation:
"r-rJ
C6Hr206+ 602 -+ 6CO, + 6HrO * enersy
Introduction
Youwill usea respirometerto measurethe rate
of respirationof germinatingand nongerminatingpea
seedsat two different temperatures.The respiromerer
consisrsoia vial,hui.o.,ru-r-?h" p.u, u'd u
volume of air' The mouth of the vial is sealel with
a rubber t -hole sropperthat has a pipet inserted
in it.
The respirometeris submergedin water.If the peas
nr" ,"rpi.i.rg, they will useoxygenand releasecarbon
dioxide' since 1 mole of carbondioxide is released
fo..u.h
oro*ygen consumed,rhereis no
changein the volume of gasin the respirometer.(Avogadro's
-oi"
Law: At constanttemperarureand
pressure'I mole of any gashas the samevolume
as 1 riole of any other gas.)you ,ltintt". thi,
equilibriumby placinga-solution of potassiumhydroxide
(KoH)'in the iiul. potrrri,,^ hydroxide
reacts
with carbondioxide to form potassiumcarbonate,
which i, u soiid.
CO, + Z KOH -+ KrCO, + H2O
since the carbondioxide producedis removed
by reactionwith potassiumhydroxide,asoxygen
is used
by cellularrespirationthe volume of gasin the
respirom","r.,"iil?".rease.As the volume of gas
decreases,
water will move into th" pip"t. Youwill usethis
decreaseof volume,asread from the scale
printed on the pipet, as a measureof th. rat"
of cellular;r;i;;;"
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Measuring Respiration of Germinating and Nongerminating Peas
Materials
Room-temperaturewater bath, cold water bath, container of ice, paper (white or lined), water,
germinating peas, nongerminating peas, glassbeads, respirometers, graduated tube, absorbent cotton
balls, nonabsorbent cotton, 15olopotassium hydroxide (KOH) solution, dropping pipets, forceps,
thermometers,stopwatch or timer or clock with second hand, calculators (optional).
Procedure
Setupof Respirometers
andWaterBatlx
You will use two water baths (uays of water) to buffer the respirometersagainst tenperature change and
to provide two tenperatures for testing: room temperature and a colder temperature (approximately
10'C). Place a sheet of paper in the bottom of each water bath. This will make the graduated pipet easier
to read. Next, place a thermometer in each tray. If necessary,add ice to the cold-temperature tray to
further cool the water to get it as close to 10'C as possible.While waiting for the cold-water temperature
to stabilize at 10'C, two of you should prepare three respirometers to test at room temperature, and two of
you should prepare an identical set of three respirtlneters to test at the colder temperature.
Preparing Peasand Gloss Beads
You will need a set of peas and/or beadsfor testing at each temperature.
Respirometer 1: Put 25 mL of H'O in your 50-mL graduated plastic tube. Drop in 25 germinaring peas.
Determine the volume of water that is displaced (equivalent to the volume of peas). Record the volume
of the 25 germinating peas. Remove these peas and place them on a paper towel.
Respirometer 2: Refill the graduated tube to 25 rnl with HrO. Drop 25 dry, nongerminating peas into
the graduated cylinder. Next, add enough glassbeads to equal the volume of the germinating peas.
Remove the nongerminating peas and beads and place thern on a paper towel.
Respirometer 3: Refill the graduated tube to 25 mL with of H2O. Add enough glassbeads to equal the
volume of the germinating peas. Remove these beads and place them on a paper towel.
Respirometer Assembly
Youwill need three respirometers
for room-temperaturetestingand three respirometers
for coldtemperaturetesting.
placean absorbentcotton ball in the bottom of eachrespirometervial. Use a
To assemblea respirometer,
withKOH.
droppingpipet to saturatethe cotton with 2 mL of 15% KOH. (Caution: Auoidskincontctct
uialsare dr1on the inside.Do notget KOH on the sidesof therespirometer.)
Be certainthat the respirometer
Placea smallwad of dry,nonabsorbentcotton on top of the KOH-soakedabsorbentcotton. The
nonabsorbentcotton will prevent the KOH solution from contactingthe peas.It is important that the
amountsof cotton and KOH soludonbe the samefor eachrespirometer.
.
Place25 germinatingpeasin your respirometer
vial(s) 1.
.
vial(s)2.
Place25 drypeasand beadsin your respirometer
.
Placebeadsonly in your respirometervial(s) 3.
Insert a stopperfitted with a calibratedpipet into eachrespirometervial. The stoppermust fit tightly. If
the respirometersleak during the experiment,you will have to start over.
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Placementof RespirometersinWater Baths
Place a set of respirometers (1, 2, and 3) in each water bath with their pipet tips resting on one lip of the
tray. See Figure 1. Vait five minutes before proceeding. This is to allow time for the respirometers to
reach thermal equilibrium with the water. If any of the respirometers begins to fill with water, you have a
leak and must start over.
Figure 1. Respirometersin the water bath.
After the equilibrationperiod,immerseall respirometers(includingpipet tips) in the water bath.
Positionthe respirometers
so that you can read the scaleson the pipets.The papershouldbe under the
pipetsto make readingthem easier.Do not put anythingelseinto the water bath or take anythingout
until all readingshave been completed.
Tal<eReadings
Allow the respirometersto equilibratefor another five minutes.Then, observethe initial volune reading
on the scaleto the nearest0.01 mL. Recordthe data in Table 1 for Time O.Also, observeand record the
temperature.Repeatyour observationsand record them everyfive minutesfor 20 minutes.
Table 1: Respirationof Peasat Room Temperature
Respirometer1
GerminatingPeas
oc
Time V of
(Mi n ) Pipet
Respirometer
2
Dry Peas+ Beads
Vof
AV Corrected Pipet
AV
Respirometer
3
BeadsOnly
AV Corrected V o f
AV
Pipet
AV
0
5
10
15
20
AV = V at Time0 - V attimeof currentre a d in g
AV = AV (forResoirometer
Corrected
1 o r Re s p iro me t 2e )r- A V o f Re s p iro me t 3
er
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Table 2: Respirationof Peasat Colder Temperature
Respirometer1
GerminatingPeas
oc 'l'ime V o f
(Min) Pipet
AV
2
Respirometer
Dry Peas+ Beads
Corrected V o f
Pipet
AV
Respirometer
3
BeadsOnly
Vof
AV Gorrected
AV
Pipet
AV
0
5
10
15
20
AV = V at Time0 - V at time of currentreading
AV = AV (forRespirometer
1 or Respirometer
2l - LV of Respirometer
Corrected
3
Analysis of Results: Measuring Respiration of Germinating and Nongerminating Peas
Graphthe datafor respirometers
1 and2 fromyourgroup'stables.Tide the graphandsupplythe
following information:
a. The independent variable is
b. The dependentvariableis
Plot the independentvariableon the x-axis,and the dependentvariableon the y-axis.Labeleach
plotted line.
1. Write two hypothesesthat this experimentis designedto test.
2. In this experiment,you measuredthe changein volume of the gasinsidethe respirometers.
The
generalgaslnw describesthe stateof a gasunder given conditions:
pV:
nRT
where p :
V :
n :
R:
T :
pressureofthe gas
volume of the gas
kmoles (numberof molecules)of gas
(K)]
universalgasconsrant[8314joules/(kmole)
gas
temperatureof the
in K
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Since you have been measuring changes in volume, restate the general gas law to solve for volume:
nRT
\/
v- - _
D
Using the generalgaslaw and your experiencein this lab, give the variablesthat had to be
controlledfor your data to be valid. State the controlsusedfor eachvariableand any meansusedto
correct for the influenceof a variable(s).
(1,2, or 3) servesasa negativecontrol?Explainyour answer.
3. Which of the respirometers
4. In referenceto the generalgaslaw, and assumingyour conffol measuresworked,a changeto which
of the variablesled to the observedchangein volume (CorrectedAV in Tables1 and 2) / Explain
your answer.
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5. Using your graph and data tables,summarizeyour findings,comparingresultsfrom respirometers1
and2, and resultsobtainedat room temperaturevs. resultsat the colder temperature.Speculateas
to the cause(s)of any differencesbetweenthe ffeatments.
6. From your graph, calculate the rate of oxygen consumption for each treatment:
a. germinating seedsat room temperature :
mL/min
b. germinating seedsat colder temperature :
c. dry seedsat room temperature:
d. d.V seedsat colder temperature:
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mL/min
mL/min
mL/min
5-6
BlacklineMaster
Analvsis of Results
Name
Date
Graphthe resultsfrom the correcteddifferencecolumnforthe g€rminatingpeasand dry peasat both room temperatureand at 10'C. Placenme rn m,ftrtes on
the x-axisand mL oxyge, consumedonthe y axis,
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