CELLULAR RESPIRATION

RESPIRATION Lab
Below is a listing which will help you to prepare for the quiz and lab on this
material.

CONTENT TO KNOW:

I. Overview of Respiration –
Respiration consists of a series of catabolic reactions which break down molecules to
release energy; creates ATP for use by the cell

C6H12O6 + 6O2 ——> 6CO2 + 6H2O

Mitochondria – the organelle in which cellular respiration occurs

II. ATP – adenosine triphosphate – energy “currency” of the cell; readily spendable

• 36 ATP – produced each time one glucose is completely “burned” using aerobic
respiration

• ADP + Pi ——> ATP (phosphorylation) – now carries energy

• ATP ——> ADP + Pi (releases energy)

Click Here for an IMAGE of ATP

III. Summary – The 3 Stages of Respiration –

Click Here for an IMAGE of the 3 Stages of Respiration

GLYCOLYSIS – Sugar “lysis” (breaks glucose into two pieces)
• End products of glycolysis = 2 pyruvate molecules
• Occurs out in the cytoplasm

THE KREBS CYCLE –
• all carbons originally in glucose are released as carbon dioxide here
• occurs in the mitochondria

ETC (ELECTRON TRANSPORT CHAIN) – electrons are passed down a series of
proteins embedded in the mitochondrial membrane; they accept and then release
electrons while harvesting energy from them

Reduction – is the gain of electrons
Oxidation – is the loss of electrons
These reactions are always coupled: hence the term REDOX

• changes NADH into ATP
• ETC occurs in the mitochondria

IV. Anaerobic Pathways –

Anaerobic – without oxygen
• Lactate (lactic acid) Fermentation (muscle cells can utilize this path)
• Alcohol Fermentation – has a decarboxylation step; produces 2 ATP

Cellular Respiration
Hands-on labs, inc.
Version 42-0040-00-01

Review the safety materials and wear goggles when
working with chemicals. Read the entire exercise
before you begin. Take time to organize the materials
you will need and set aside a safe work space in
which to complete the exercise.

Experiment Summary:

Students will measure the rate of cellular respiration
using millet seeds growing in a respirometer.
Students will design an experiment to study how
different conditions can affect cellular respiration
and will compare the rates with a control.

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ExpErimEnt

ObjEctivEs
● To measure the rate of cellular respiration

● To observe how different conditions affect cellular respiration

Time Allocation: Exercise 1 requires 2–3 days of advance preparation for germination of seeds.

Actual experiment: 3 hours

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Experiment Cellular respiration

matErials

MATERiAlS
FRoM:

lABEl oR
BoX/BAg: QTy iTEM DESCRiPTioN:

Student Provides 3 Cotton balls
1 Water, distilled
1 Light source, such as a 100-W bulb
1 Towels, paper
1 Stopwatch or Timer
1 Tape, clear

LabPaq Provides 2 Cup, 9 oz plastic

1

Dissection-kit with 7-tools – including the
following: Bent Probe, Dropping Pipet, Probe,
Ruler in pocket, Scalpel with 2 Blades – Note
blades are in the pocket, Scissors, Tweezers

2 Pipets, Empty Long Stem
2 Seed, Millet – 200+ in 2”x3” bag
1 Sodium Hydroxide, NaOH 0.5M, 1mL in Pipet
1

1

2

Marking pencil

Petri dish, 90 mm

Test Tubes

Note: The packaging and/or materials in this LabPaq may differ slightly from that which is listed
above. For an exact listing of materials, refer to the Contents List form included in the LabPaq.

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Experiment Cellular respiration

DiscussiOn anD rEviEw
Energy is an important component of life. All cells exchange energy with their environment and use
this energy for internal processes, growth, and repair. Organisms consume energy obtained from
an outside source, either from the Sun or from other organisms, to undergo cellular respiration.
Certain organisms, such as plants and specific bacteria, can trap the energy from the sun and
store this energy through a process called photosynthesis. However, many organisms must obtain
their energy from eating other organisms.

Cellular respiration is the process of transferring energy that is stored chemical bonds (such as
the chemical bonds of carbohydrates, fats, and proteins) to a usable form of energy in the cell:
a molecule called adenosine triphosphate (ATP). The cell can use the energy that is released
when the last phosphate bond of ATP breaks and convert it into other forms of energy, such
as mechanical energy for movement. However, in the process of this conversion, the organism
consumes oxygen and produces the waste product carbon dioxide (CO2). See Equation 1 for a
basic representation of respiration in an organism using glucose as energy:

Cellular respiration can occur either in the presence of oxygen, as in aerobic respiration, or in
the absence of oxygen, which is referred to as anaerobic respiration. Anaerobic respiration is far
less efficient: much less ATP is produced per amount of energy consumed. In addition, anaerobic
respiration cannot last as long as aerobic respiration and produces unwanted byproducts. For
these reasons, aerobic respiration is the preferred use of energy for cells.

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Experiment Cellular respiration

Exercise 1: Cellular Respiration in Plants
iMPoRTANT: Germinate the seeds 3 days ahead of time; see Steps 1–4.

In this exercise, you will observe germinating seeds in order to measure aerobic cellular
respiration. The rate of respiration is determined by measuring the production of carbon dioxide.
Plants undergo both cellular respiration and photosynthesis. It is difficult to measure the amount
of CO2 given off during respiration if it is also being consumed in the photosynthetic process.
To eliminate this variable, you will conduct your control experiment before the seeds undergo
photosynthesis, which is when the leaves germinate from a plant.

To offset the production of CO2, sodium hydroxide (NaOH) will be added to the test tubes. The
sodium hydroxide should interact with the gaseous form of CO2 to form solid sodium bicarbonate
(NaHCO3) − common baking soda. The simplified equation for this process is:

CO2 + NaOH à NaHCO3

Because the CO2 is taken out of the air to form the precipitate, the change in air levels within the
test tubes will give an indirect measure of the uptake of oxygen in cellular respiration.

prOcEDurE
1. Before beginning, set up a data table similar to the Data Table 1 in the Lab Report Assistant

section.

2. Moisten a paper towel, but do not oversaturate it with water. Fold the paper towel and place
into the bottom of the petri dish so it fits completely in the dish.

3. Spread half of the millet seeds (200 seeds) on top of the moistened paper towel. Place the top
half of the petri dish over the seeds and place the seeds in a dark, warm location.

4. Save the remaining half of the seeds for use later in the exercise.

5. Do not move the seeds for two or three days. Check on the seeds daily to ensure that they
stay moist. After two or three days, the seeds should show signs of germination.

6. Once approximately 100 seeds have germinated, move on to the next step. Note: you will use
approximately 100 seeds that have germinated below, and you may want to save the other
100 seeds that have or have not germinated yet in the petri dish in case you want to repeat
the experiment.

7. Place a test tube next to the ruler from the dissection kit as shown in Figure 1, with the open
end of the test tube at the 0-cm mark. Using the marking pencil, mark the test tube in 5-mm
(0.5-cm) intervals, until 6.0 cm have been marked off. Mark both test tubes. See Figure 1 for
guidance.

8. Label one test tube with a “C” for the control, and label the other with a “G” for germinating
seeds.

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Experiment Cellular respiration

Figure 1:

9. Use the tweezers from the dissection kit to pull cotton balls apart into six smaller cotton balls
of approximately 1 cm thick. See Figure 2 for guidance.

Figure 2:

10. Gently drop 100 germinated seeds into the test tube marked “G,” and from the 2nd bag of 200
dry seeds, place 100 dry non-germinated seeds into the test tube marked “C.”

11. After the seeds are in place, add a small ball of dry cotton 1 cm thick to each test tube. Use a
long-stem pipet to push the cotton into place in the test tube so that the seeds and cotton are
at the closed end of the test tube. See Figure 3.

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Experiment Cellular respiration

Figure 3:

12. Cut off the tip of the 0.5 M NaOH pipet. WARNiNg: This is a strong base, and safety precautions
should be taken to ensure that it does not come into contact with any mucous membranes
or skin.

13. Place 15 drops of 0.5 M NaOH into a clean plastic cup. Add 15 drops of distilled water to this
solution. This addition will create a 0.25 M solution. Stir the solution with a long-stem pipet.
Be careful not to spill any of the solution on any surfaces or on your skin, as it is very caustic.

14. Place the two cotton balls you prepared in Step 9 into a second clean plastic cup. Use the long-
stem pipet from Step 13 to draw up some of the 0.25 M NaOH solution, and put four drops
on top of each cotton ball.

15. Use the tweezers from the dissection kit to turn the cotton balls over, and put four more drops
of the solution on the other side of the cotton balls.

16. Use the tweezers to gently squeeze the cotton balls before placing one in each test tube. Push
the cotton balls toward the end of the test tube using the long-stem pipet (ensure that the
pipet is empty).

17. Wash and rinse the cup that was used for dropping the 0.25 M solution on the cotton balls
with soap and water. Fill the cup about half-full with distilled water.

18. Place the test tubes upside-down in the water and tape the test tubes to the sides of the
plastic cup, so the bottoms of the test tubes do not touch the bottom of the cup. See Figure 4.

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Experiment Cellular respiration

Figure 4:

19. Position the plastic cup with the test tubes next to a light source. The light source is used to
keep the seeds warm so they will respire more quickly. See Figure 5.

Figure 5:

20. Begin timing the experiment, and note the beginning water level for each of the test tubes.
Record this “Starting Level of Water” in Data Table 1.

21. After 30 minutes, note the water level of the test tubes. Write this water level in Data Table 1
under “Water Level: 30 min.”

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Experiment Cellular respiration

22. After 1 hour and 1.5 hours, note the levels of the water in the test tubes again. Write the data
in Data Table 1, under “Water Level: 1 hour,” and “Water Level: 1 hour, 30 min,” respectively.

23. Thoroughly clean all equipment with soap and water, and dispose of seeds and cotton balls in
the trash after use. Use the tweezers from the dissection kit to remove cotton balls, and shake
seeds out of test tubes to dispose of them.

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Experiment Cellular respiration

Cellular Respiration

Hands-on labs, inc. Version 42-0040-00-01

LAB REPORT

PHOTOS – Include the digital photos as attachments or place them right into your report.

Photo #1 – Take a photo which is a CLOSE UP of the seeds AFTER they have germinated, while still in the petri dish.

Photo #2 – Take a photo of your experimental set up with the two tubes in the glass, AT THE END. Get close enough that the results show in both tubes. Set up your tubes side by side on the same side of the glass so this can be done. You may need to put BLACK PAPER or a dark background behind the glass, to reduce glare.

Data Table 1: Oxygen Consumption Measured by Change in Water Level
Starting Level of

Water

Water level:

30 min

Water level:

1 hour

Water level:

1 hour, 30 min

Experiment
Control

Questions

A. Why use germinating seeds to detect cellular respiration?

B. Explain how the movement − or lack of movement − of the water in the respirometer is a reflection of cellular respiration.

Experiment

Cellular respiration

202

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C. What is the role of the NaOH-saturated ball of cotton in the respirometer? What would have

occurred if it were not in place?

D. In photosynthesis what is the reactant gas and what is the product gas?

In respiration what is the reactant gas and what is the product gas?

What is the elegant relationship between these gases and these two different processes?

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LAB REPORT

PHOTOS

Include

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as attachments or place them right into your report.

Photo #1

Take a photo which is a CLOSE UP of the seeds AFTER they have germinated, while still

in the petri dish.

Photo #2

Take a photo of your experimental set up with the two tubes in the glass, AT THE END.

Get close enough that the results show in both tubes. Set up your tubes side by side on the same

side of the glass so this can be done. You may need to put BLACK PA

PER or a dark background

behind the glass, to reduce glare.

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Experiment

Cellular respiration

20

2

©Hands-On Labs, Inc.

www.LabPaq.com

Cellular Respiration

Hands-on labs, inc. Version 42-0040-00-01

LAB REPORT

PHOTOS – Include the digital photos as attachments or place them right into your report.

Photo #1 – Take a photo which is a CLOSE UP of the seeds AFTER they have germinated, while still

in the petri dish.

Photo #2 – Take a photo of your experimental set up with the two tubes in the glass, AT THE END.

Get close enough that the results show in both tubes. Set up your tubes side by side on the same

side of the glass so this can be done. You may need to put BLACK PAPER or a dark background

behind the glass, to reduce glare.

Data Table 1: Oxygen Consumption Measured by Change in Water Level

Starting Level of

Water

Water level:

30 min

Water level:

1 hour

Water level:

1 hour, 30 min

Experiment

Control

Questions

A. Why use germinating seeds to detect cellular respiration?

B. Explain how the movement – or lack of movement – of the water in the respirometer is a

reflection of cellular respiration.

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