Name ____________________
Cellular Respiration & Excretion Lab *
Biology
*Adapted from lab created by Sandy Latourelle
Purpose: In this exercise you will determine the amount of carbon dioxide produced by
cellular respiration and compare students in your class. You will be able to use this
information to gauge the respiration rate of your cells and thus the metabolic rate of the
human body.
Background information: Cellular respiration is the process by which cells extract
usable energy from the chemical bonds of food molecules (usually glucose). The energy
extracted is in the form of ATP which can be used immediately for various energy
requiring cellular activities. Cellular respiration also creates the waste products carbon
dioxide & water which are eliminated by the cell when these molecules diffuse into the
bloodstream. The blood carries these wastes to the air sacs of the lungs (alveoli) where it
is removed from the blood & exhaled from the body. Measurement of carbon dioxide is
therefore a simple method of determining the rate of cellular respiration (metabolism) of
the cells in the body.
The unit we will use to measure carbon dioxide production is the micromole.
Every element has an atomic weight (equal to the number of its protons & neutrons). The
element hydrogen (H) for example has an atomic weight of 1. Oxygen (O) has an atomic
weight of 16. These atomic weights contribute to the weight of a molecule. For example
H2O has a molecular weight of 18 (H molecular weight is1 X 2 molecules of H + O
molecular weight =16). A mole of any substance is its molecular weight in grams.
Applying these concepts CO2 has a molecular weight of 44 grams (C molecular weight is
12 + O molecular weight is 16 X 2 molecules of O). However, because 44 grams of CO2
is a very high volume of this gas, it is not convenient to measure CO2 production in
moles. Micromoles which are millionths of a mole are used instead.
The determination of CO2 in this lab will utilize the indicator phenolphthalein,
which is a chemical whose color changes to pink in the alkaline pH range (pH 8 through
14).
Materials:
100 ml graduated cylinder
Erlenmeyer flask
Phenolphthalein indicator
Rubber gloves
10 ml graduated cylinder
0.04% NaOH solution
pipette
apron
goggles
straw
stopwatch
Procedure:
1. You must determine the number of drops of NaOH solution in 1 ml. Add
NaOH to a 10 ml graduated cylinder until you have 1 ml. Count the number of
drops you add to the cylinder!! Record this value in you data table.
2. Measure 100 ml of tap water into a graduated cylinder and pour into your flask.
3. Add 5 drops of phenolphthalein indicator to your flask.
4. Add enough drops of 0.04% NaOH solution to mtach the pink color of your
teacher’s prepared flask.
CAUTION: NaOH IS A STRONG ALKALI; AVOID GETTING IT ON YOUR
SKIN OR CLOTHING!
5. Blow through your straw into the solution for exactly one minute. Breathe in
normally without the straw but exhale normally through the straw. Blow gently so
that the water will not splash from the flask.
6. Titration: Slowly & carefully, using a pipette add 0.04% NaOH drop by drop to
your flask while gently swirling the flask with your other hand. Add NaOH until
the pink color remains. Record the number of drops of NaOH you added to you
data table.
7. Using the information you collected in step 1, convert drops of NaOH into ml of
NaOH. Record this value in your data table.
8. Convert ml of NaOH to micromoles of CO2 exhaled per minute. Multiply the
number of ml of 0.04% NaOH used to turn your solution pink by 10. Record this
value in your data table.
9. On the board, record your name & the number of micromoles of CO2 you exhaled
in a minute.
10. When all of your classmates have recorded their CO2 values on the board,
calculate & record the class average in the data table.
Data Table
Drops of
NaOH in 1 ml
Drops of
NaOH to turn
solution pink
Volume of
NaOH to turn
solution pink
(ml)
CO2 exhaled
per minute
(micromoles)
Class average
CO2 exhaled
per minute
(micromoles)
Questions
1. What is the importance of using the phenolphthalein indicator & standardized
solution to your results?
2. What is the class average of CO2 in micromoles per minute?
3. Do all the members of your class exhale the same amount of CO2 in micromoles
per minute?
4. What is the significance of the observed variation among class members?
5. Since CO2 is a product of cellular metabolism, what does the amount of CO2
exhaled per minute tell you about the metabolism of the individuals in your class?
6. Write the equation for the process of cellular respiration.
7. In your answer to the above question, circle the product that is the most useful to
the cell.
8. How would the results to this activity vary if you just ran the mile in physical
education class?
9. Summarize the importance of cellular respiration to living organisms.