Cellular Respiration Lab
Lab Design Tutorial
Instructions
• Use this tutorial along with the lab papers and
sample lab materials to help your group
understand the details of this lab
• Follow the directions on the instruction paper
• When your group feels confident that you
understand all aspects of the lab, come up to
the teacher for your oral quiz!
• Click on the buttons (like the one below) to
advance…
NEXT… 
Review Questions
• What is the equation for cellular respiration?
C6H12O6 + 6 O2  6 CO2 + 6 H2O + 686 kcal/mol
• Discussion Questions:
– What could you measure in an experiment that
tests the amount of cellular respiration?
NEXT… 
Focusing on one variable…
• You could use any of the reactants or
products, but for this experiment we are going
to measure change in oxygen over time.
• What will you observe in this experiment as it
progresses? (click on one)
O2 will
DECREASE
O2 will
INCREASE
Correct!
• Since oxygen is consumed during cellular
respiration, the amount of O2 will decrease as
more cellular respiration occurs.
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continue
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Background - Gases and Pressure
• Oxygen (O2) is a gas.
• You will measure the amount of gas by
measuring the pressure of the gas.
• Pressure = amount of force exerted on the
walls of container by the molecules of gas.
NEXT… 
Gases (continued)
• Click on the link below to review the
relationship between pressure and the
number of gas molecules.
• http://legacyweb.chemistry.ohiostate.edu/betha/nealGasLaw/fr2.2.html
NEXT… 
Check your understanding…
• Discuss the following questions with your lab
group:
• What happens to the pressure when the
number of gas molecules increases?
• What happens to the pressure when the
number of gas molecules decreases?
• What is the relationship between pressure and
volume?
Click HERE for answers
Gases… Answers
• The relationship between number of gas
molecules and pressure is directly
proportional
– When # of gas molecules increases, so does
pressure
– When # of gas molecules decreases, so does
pressure
NEXT… 
Gases… (Answers)
• The relationship between volume and
pressure is inversely proportional.
– When volume INCREASES, pressure DECREASES
– Discuss WHY with your lab group.
• The relationship between temperature and
pressure is directly proportional.
– When Temperature INCREASES, so does pressure
• Wait… I think I remember something like this
from Chemistry…
NEXT… 
Ideal Gas Law
• PV = nRT
– P = pressure
– V = volume
– n = # of moles of gas
– R = Gas constant
– T = temperature
NEXT… 
Using the Ideal Gas Law
• In this experiment, we are going to be
measuring pressure. So, the equation can be
rewritten like this:
P = nRT/V
NEXT… 
Experimental Set-up
• This lab will use the respirometer to measure
the change in oxygen pressure
• Any living organism that fits in the vial can be
used.
NEXT… 
Linking to the ideal Gas Law
• Considering the Ideal Gas Law, how do we
make sure we are only dealing with 1
variable?
– Lab Design: In order to make the experiment
valid, there can only be one unknown factor
(dependent variable). This means all the other
variables should be held constant.
– Which of the variables in the Ideal Gas Law
equation is the dependent variable (what is being
measured)? (CLICK ON ONE)
Temperature
Pressure
Volume
CORRECT!
• Pressure (of oxygen) is what you will be
measuring the change in, so this is your
dependent variable.
• The volume is held constant because the glass
vial doesn’t change in volume throughout the
experiment (and the volume taken up by
organism is also held constant).
• Temperature will be held constant with the
water bath
NEXT… 
Hold on… O2 isn’t the only gas!
• CO2 is also produced during cellular
respiration.
• So how will we make sure the pressure
measured is only O2?
– Change the CO2 into a solid so it doesn’t
contribute to the pressure measurement!
– How? Use KOH to convert it
NEXT… 
– CO2(g) + 2 KOH(s)  K2CO3(s) + H2O
KOH Soaked
Cotton
O2 (g)
CO2 (g)
How will you SEE the change in O2
pressure?
• Use the water bath
• When you put the respirometer into the water
bath, what happens?
– Hint: Think about where the pressure is higher.
Inside or outside the respirometer?
– Given this consideration, where will water go?
Why?
NEXT… 
High to Low… 
• Water will rush into the Pipette
• Why?
• Because the pressure outside (in the water) is
higher than the pressure inside the vial
• Discussion question: When will the water
stop moving into the pipette?
NEXT… 
How will you measure CR in this lab?
• Discuss these questions with your group:
• As the organism performs cellular respiration,
what will happen to the pressure in the
respirometer vial?
• What will you see happen in the pipette?
• Why? (Link this back to the Ideal Gas Law)
NEXT… 
Animation
• Click below for an animation of a respirometer
• http://www.phschool.com/science/biology_pl
ace/labbench/lab5/respwork.html
NEXT… 
Control
• What is the control for this experiment?
– Glass beads in the respirometer instead of live
organism
• Why?
• Discuss:
– Why this would be a control for the experiment
with your lab group?
– How will it be used quantitatively (how will you
use it to adjust the readings you get for your live
organism)?
NEXT… 
THE END!
Please follow the instructions
on the orange paper and
review with your group until
you are ready to be tested