Qualitative Cellular Respiration
(Adapted from: State Adopted – Prentice Hall Laboratory Manual B)
Objectives:

Explain the interrelated nature of photosynthesis and cellular respiration.

Relate the structure of the major plant organs and tissues to physiological processes.
Purpose of Lab/Activity:

To understand how photosynthesis and cellular respiration work hand-in-hand.

To observe how cellular respiration occurs under aerobic conditions.
Prerequisites: Prior to doing this lab, students should have been taught about cellular respiration including lactic acid fermentation, alcoholic fermentation, glycolysis, the Krebs cycle, and the electron transport chain. Students should also be aware of how photosynthesis and cellular respiration go hand-in-hand. The products of one process are the reactions of the other and vice versa.
Problem Statement: How do organisms release energy from food?
Background:
All living things undergo respiration. During this process, food molecules are broken down. As part of this process, animals take in oxygen and release carbon dioxide by breathing, which is easily observable. Plants do not “breathe” as animals do, so respiration in plants is not as easily observable. How do we know that plants respire?
In this investigation, you will observe the release of carbon dioxide by humans. You also will perform an experiment to determine whether plants release carbon dioxide as a product of cellular respiration.

Purple cabbage indicator is a purple liquid turns red when mixed with an acid and blue when mixed with a base.

Keep in mind that carbon dioxide will combine with water to form carbonic acid.

Also keep in mind that plants carry out respiration (however, when exposed to light, they also perform photosynthesis, which reduces carbon dioxide levels)
For more background, open “Photosynthesis & Cellular Respiration Rates in Plants”
Safety: Wear goggles at all times in the science laboratory. To avoid burns, exercise caution when working with the hot plate and heated materials. Be careful not to inhale any of the cabbage indicator
Vocabulary: aerobic respiration, alcoholic fermentation, anaerobic respiration, cellular respiration, electron transport chain, glycolysis, Krebs
Cycle, lactic acid fermentation
Extension: Cell Energy Cycle Gizmo
Pre-Lab Questions:
Read the entire investigation. Then, work with a partner to answer the following questions.
1.
Breathing is actually a part of what biological process?
2.
What is cellular respiration?
3.
How are the processes of photosynthesis and cellular respiration related?
4.
What are the reactants and products of cellular respiration?
5.
Where does most of the cellular respiration steps take place in eukaryotic cells?
6.
What gas is exhaled during breathing?
7.
When the cabbage is mixed with the boiling water, what color do you expect the water to turn?
8.
When cabbage pH indicator solution is added to an acid (or an acid is added to it) what happens to its color?
9.
What does the cabbage pH indicator solution actually test for?
10.
If the substance detected by cabbage pH indicator solution is not same substance produced during cellular respiration, how can it can be used as indicator of cellular respiration?
11.
How are we going to find out if plants perform cellular respiration in this experiment?
12.
What do you hypothesize will happen in part A of the experiment? Why?
13.
What do you hypothesize will happen in part B of the experiment? Why?
14.
In Part B, what is the function of test tubes B & C?
15.
What is the purpose of covering tubes with aluminum foil?
16.
What special safety note should you observe when you blow through the straw.

Materials (per group):

Cabbage pH indicator (Or other pH indicator)

Calculator

Cotton Balls

Forceps

Germinating Seeds (Soaked, see below)

Glass Beads

Graduated Cylinder (100ml)
Procedures:
Part A. Cellular Respiration in Animals
1.
Prepare Cabbage pH indicator solution (See Acids & Bases Lab for more information) or other valid indicator solution.
2.
Label test tubes A, B , C, D
3.
Fill 1/3 of test tube A with cabbage pH indicator solution.
4.
Use a straw to exhale into the solution in tube A for 30 seconds.
Note: ONLY EXHALE INTO THE STRAW. DO NOT INHALE INTO THE
STRAW OR YOU WILL END UP WITH A MOUTHFUL OF PURPLE
CABBAGE INDICATOR. WHEN YOU NEED TO TAKE A BREATH, COME

Non-Germinating Seeds

Paper Towels

Rubber Stoppers

Straw

Culture Tubes x 4

Culture Tube Rack

Tray (to soak seeds for germination)
AWAY FROM THE STRAW; TAKE YOUR BREATH, AND THEN EXHALE
INTO THE STRAW. Record your observations in the Data Table.
Part B. Cellular Respiration in Germinating Seeds (Plant Seed Respiration!)
Prep:
1.
24-48 hours prior to the lab, soak seeds in water to make them germinate. The night before the lab, remove seeds from water and pat them dry on a paper towel. Keep them wrapped in the paper towel until they are used on the next day.
2.
To create proper comparison, we will use equal volumes of treatment in all our groups. Therefore, as a first step we need to measure equal volumes of germinating seeds, non-germinating seeds, and glass beads (This step can be omitted at the chance of small result bias).
A) Measure Germinating Seed Volume (Water Displacement Method):

Use a 100 ml graduated cylinder to measure 50ml of water; B) Add 10 germinating seeds; C) Measure volume again;
D) Seed volume = C – A.

Remove seeds and pat them dry.
B) Calculating necessary number of non-germinating seeds and glass beads to match volume of germinating seeds
(May be performed by teacher ahead of time)
Beads:

Use a 100ml graduated cylinder to measure 50ml of water; B) Add 100 glass beads C) Measure volume again; D) Average glass bead volume = (C-A) / 100.

Number of beads required = 1D / 2D

Alternative = Use a 100ml graduated cylinder to measure 50ml of water; B) Add glass beads 1 by one until volume of germinating seeds from 1D is matched. Use those very same beads in experiment (make sure they are patted dry)
Non-Germinating Seeds:

Use a 100ml graduated cylinder to measure 50ml of water; B) Add 100 non-germinating seeds C) Measure volume again; D)
Average non-germinating seed volume = (C-A) / 100.

Based on the average glass bead volume from above and on this average volume of non-germinating seeds, calculate amount of glass beads necessary to complete the volume of 10 non-germinating seeds so it matches the volume of 10 germinating seeds

Do not use the seeds used in the estimating procedure during the experiment. Since these seeds were submerged in water, they probably absorbed some (which may cause them to germinate) and thus bias the results. For the same reason, the alternative procedure used above to directly measure glass bead volume cannot be used with non-germinating seeds.
Lab:
1.
Label 3 test tubes A, B, & C using a marker and masking tape
2.
Fill 1/3 of test tubes with cabbage pH indicator solution
3.
Use a forceps to place a small layer of cotton ball over the cabbage pH indicator solution. It is very important that the cotton never actually touches indicator solution so leave some room. If it does touch it, you must remove it and place a new one. Place enough cotton to fill tube to the 2/3 level.
4.
Place 10 germinating seeds over the cotton ball in tube A, equal volume of glass beads + non-germinating seeds in tube B, and glass beads only in tube C
5.
Note color of indicator solution on test tubes
6.
Place rubber stopper on all tubes and cover all containers with aluminum foil
7.
Place the test tubes in a test-tube rack and after 24 hours, record any changes
Note: If there are no changes after 24 hours, wait another day.

Alternatives:

Instead of placing seeds directly above indicator solution in a tube with a rubber stopper (water from indicator may evaporate, be absorbed by cotton / seeds and bias the results), place a paper towel in the bottom of a jar, place seeds or beads over the paper towel, place a test tube with indicator solution open inside the jar, and then close the lid in the jar. For this method more seeds should be used.

Also, note that peas or any other kind of plant seeds can be used.

Use respirometer setup to measure carbon dioxide production (See AP LAB 5 – Cellular Respiration)
Results:
DATA TABLE
Test Tube Solution Color
Date
Germinating Peas
(Tube A)
Dry Peas + Beads
(Tube B)
Glass Beads
(Tube C)
Analysis / Discussion Questions:
1.
How did the color of the indicator solutions change over time?
2.
Compare results with that of other groups in your class (remember that repletion is important for validity)
3.
Did the results support or fail to support your pre-lab predictions?
4.
Explain what happened to indicator in Part A.
5.
How does it prove animals perform cellular respiration?
6.
Explain the differences between the tubes in Part B.
7.
Compare the reaction that occurred in the test tube that contained the seedlings with the one that occurred in the test tube into which you exhaled. How are they similar? Why the similarity?
8.
Why is the process of cellular respiration common to most life forms?
9.
Why do most living things take in oxygen?
10.
Based on this experiment, what have your learned about cellular respiration? Do animals breathe? What about plants?
INQUIRY EXTENSION:

Students design their own variations of this experiment following all steps of the scientific method with focus on manipulating conditions around the germinating seeds and seeing if it affects the production of carbon dioxide (pH, temperature, light, pollution, etc)

All experimental designs must include at least 3 levels of the independent variable (control + 2)

All experimental designs must include repetition (students do it 3 times or do all 3 times all at once, which would require several jars/test tubes)

You may use the available foods and chemicals or bring in your own.

At the conclusion, groups will have to submit full lab reports in accordance with lab report template / rubric

Before doing the lab, submit the following to the teacher: Problem Statement / Background / Material List /Procedure
Note: Before you write a full background you may want to check you problem statement and a preliminary idea of how to test it with the teacher. Students often decide to switch experiments after they realize their procedures are not practical. At that point, you may have wasted your time already writing a full background)