Lab Exercise 7 - Cellular Respiration
Anaerobic and Aerobic Metabolism
Introduction:
Cellular respiration occurs in most cells of both plants and animals. Cells must continually obtain
energy from the environment and use it to make adenosine triphosphate or ATP. ATP is used later in
cellular work. Cells may extract energy from organic food molecules such as carbohydrates, fats, and
proteins. Cells do not breakdown molecules in a single reaction; instead, the breakdown occurs in a
long sequence of reactions.
The two important pathways to extract energy from nutrients include aerobic respiration and
anaerobic respiration (fermentation). Some organisms carry out their energy producing reaction in
the complete absence of oxygen, a process known as anaerobic respiration. Fermentation is an
anaerobic process because oxygen is not used in the process. Other organisms use oxygen in their
metabolic process and are said to carry out aerobic respiration.
Objectives:
Upon completion of this exercise, you should be able to:
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6.
Explain cellular respiration in both aerobic and anaerobic respirations.
Understand the general reactions and products of aerobic respiration and fermentation.
Describe the stages for aerobic and anaerobic respirations
Describe the use of O2 and the production of CO2 in cellular respiration.
Explain the relationship between cellular respiration and photosynthesis.
Define all the terms that are bolded and underlined.
Cellular Respiration: (Figure 7.1):
Cellular respiration is the general term which describes all metabolic reactions involved in the formation
of usable energy from the breakdown of nutrients. In living organisms, the "universal" source of energy
is ATP.
Aerobic Respiration Summary Reaction
C6H12O6 + 6O2 ------------> 6CO2 + 6H2O + 36ATP + heat
(Glucose)
Anaerobic Respiration Summary Reaction of Alcoholic Fermentation
C6H12O6 ------------> 2ethyl alcohol + 2CO2 + 2ATP + heat
(6 carbons)
(2 carbons each)
Summary Reaction of Lactic Acid Fermentation
C6H12O6 ------------> 2 lactic acid + 2ATP + heat
(6 carbons)
(3 carbons each)
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Heat is produced in both fermentation and aerobic respiration because living cells are never 100%
efficient in transforming energy from one usable form (like food molecules) to another usable form (like
ATP). A certain amount of energy is always released in a form that cannot power reactions within the
cell (heat). Although heat cannot directly power reactions within a cell, it is important in controlling the
rate of chemical reactions. The higher the temperature of a cell (up to a point), the faster enzymatic
reactions will occur.
In some organisms, the temperature of the body changes with the temperature of the external
environment. In such cases, the hotter the environment, the higher the body temperature and the faster
the rate of chemical reactions within the body occur. Such organisms are referred to as poikilotherms
(poikilo = varies, therm = heat). Example: The fungus yeast is a poikiloterm that we will use in this lab.
Some organisms maintain a constant body temperature despite changes in the external environment.
They are called homeotherms (homeo = same). The heat to maintain their body temperatures comes
from cellular respiration reactions within the body.
Figure 7.1 - Cellular Respiration Overview
Steps of Cellular Respiration:
Cellular respiration is subdivided into the following three metabolic stages: glycolysis, Krebs
cycle, and electron transport chain.
1. Glycolysis: (Figure 7.2 and 7.3):
The first stage of cellular respiration is glycolysis, the breakdown of glucose (a six-carbon sugar) to
form two molecules of pyruvic acid (pyruvate). Glycolysis takes place in the cytoplasm of the cell.
The resulting pyruvate may pass through one of several pathways, depending on the organism in
question. In some organisms, such as yeast, fermentation occurs. In other organisms, aerobic
respiration occurs. Glycolysis also produces 2 molecules of energy carrying NADH, which moves
to the electron transport chain (ETC), and 2 molecules of ATP.
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Figure 7.2 - Glucose Molecule
Figure 7.3 - Formation of Pyruvic Acid
In an intermediate stage, (Figure 7.4): pyruvic acid is converted into acetyl coenzyme A after
pyruvic acid arrives in the mitochondria. Pyruvic acid is oxidized through a series of steps into a
compound called Acetyl–CoA that also reduces NAD+ to NADH.
Pyruvic acid is first altered in the transition stage by removal of a carbon and two oxygen atoms
(which combine to form carbon dioxide). When the carbon dioxide is removed, energy is given off,
and NAD+ is converted into the higher energy form NADH. Coenzyme A attaches to the remaining
2-C (acetyl) unit, forming acetyl CoA. This process is a prelude to the Krebs cycle.
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Figure 7.4 - Formation of Acetyl Coenzyme A
2. The Krebs cycle: (Figure 7.5)
The Krebs cycle takes the acetyl CoA from glycolysis and completely oxidizes it to carbon dioxide.
In the process, 2 ATP molecules are gained. The Krebs cycle yields much more energy than
glycolysis. Most of the energy produced by this cycle of reactions is not in the readily usable form of
ATP; instead, it is NADH and FADH2. Their energy must be transferred to phosphorylate ADP
molecules (add a phosphate) by the electron transport chain (ETC) to be readily usable. In the Krebs
cycle, for each acetyl CoA that goes into the cycle, three molecules of NADH, one molecule of
FADH2, and one molecule of ATP are formed (= 6 NADH, 2 FADH2, and 2 ATP per whole
glucose).
Figure 7.5 - Kreb's Cycle
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3. Electron Transport Chain: (Figure 7.6):
The electron transport chain or ETC is a system of electron carriers embedded into the inner
membrane of a mitochondrion. These compounds act to accept energy bearing electrons from
NADH and FADH2 and transfer them step-by-step to free oxygen. The oxygen is reduced by these
electrons combing with hydrogen to form water. At each of several transfer steps, some energy is
liberated and at some steps, enough energy is liberated to create an ATP molecule from ADP and
free phosphate. The net result is that 1 molecule of NADH can release enough to create 3 ATP
molecules and 1 FADH2 can create 2 ATP molecules.
By using the electron transport system to convert all the energy to ATP’s, 34 ATP molecules are
produced.
Figure 7.6 - Electron Transport Chain
Energy yields for aerobic respiration as discussed above, is given in the Table 7.1.
Table 7.1 - Net ATP Yield
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Lab Activity 7 - Cellular Respiration
Anaerobic and Aerobic Metabolism
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9 Test tubes
Test tube Racks
Bromthymol blue solution
Droppers 12 numbers
Plastic/Glass Beads 20
6 to 10 germinating (pea) seeds
6 to 10 dry seeds
drinking straw 4
rubber bulbed syringe
two thermos bottles
2-holed rubber stoppers to fit the thermos flask – 2 numbers
1000 ml beaker
150 gm of sucrose
Water Bottle
800 ml of Warm Water
Marker
Label saying ‘Control’ and ‘Experimental’
Yeast
Plastic / Rubber tubing 2 numbers
Thermometers – 2 numbers
250 ml conical flask – 2 numbers
One holed rubber stopper to fit the conical Flask -2 numbers
Glass tubing - 2 numbers
Limewater
Metal stand
2 green leaves
Forceps
Rubber stopper to fit the test tubes – 3 numbers
Aluminum foil
Assignment 1
To determine whether air exhaled from your lungs contains an accumulation of CO2
Procedure:
a)
b)
c)
d)
Place 30 drops of Bromthymol blue into each of 2 test tubes numbered 1 and 2.
Exhale through a drinking straw in to tube 1 for 5 minutes.
Use a rubber bulb syringe to pump atmospheric air into tube 2 for 5 minutes.
Record your results/ any color change in the Bromthymol blue solution in the tubes under
assignment 1 of the lab report.
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Assignment 2 - A demonstration has been set up and will be discussed by your instructor.
Respiration and Carbon dioxide
In this assignment you will determine whether cells of living organisms produce carbon dioxide by
cellular respiration. The presence of CO2 may be detected by using dilute Bromthymol blue solution (a
pH indicator). As CO2 accumulates, it causes a decrease in pH (an increase in acidity) by combining
with water to form carbonic acid that in turn releases hydrogen ions (H+) as it dissociates. The
hydrogen ions react with Bromthymol blue and cause it to turn from blue to green and then to yellow as
more and more acid is produced/ more CO2 released.
Procedure: (Figure 7.7).
a) Place 15 drops (0.15ml) of 0.004% Bromthymol blue into each of three test tubes numbered
one through three (1-3).
b) Place several glass beads or short lengths of glass tubing into each tube so that the seeds
are kept out of the solution.
c) Place 6 to 10 germinating seeds in tube 1
d) Place 6 to 10 dry seeds in tube 2. Place nothing in tube 3.
e) Insert a rubber stopper into each tube.
f) Place the tubes in a test tube rack for 1 hour. Then observe any color change in the
Bromthymol blue in each test tube and record your results under assignment 2 of the lab
report.
Figure 7.7 - Insertion of beads and seeds to Bromthymol blue solution
Assignment 3 - A demonstration has been set up and will be discussed by your instructor.
Measuring the release of energy from sucrose: Figure 7.8a & b.
Procedure:
a) Select two thermos bottles. Label one of the bottles Flask 1, which is the control and the
second bottle Flask 2, which is the experimental. To a 1 liter or 1000 ml beaker, add 150 gm of
sucrose to 800 ml of warm water and stir until dissolved.
b) Pour half of the sucrose solution into the insulated bottle marked “control”.
c) Add a packet of yeast to the sucrose solution left in the mixing beaker and stir. Pour the sucrose
and yeast mixture into the thermos bottle marked “experimental”.
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d) Close the thermos bottles with 2-holed rubber stoppers. Insert a thermometer into one hole of
each of the stoppers so that the bulb is in the liquid within the bottles.
e) Insert glass tubing through the second hole making sure it does not touch the liquid in the
thermos bottle (as demonstrated by your instructor).
f) Connect the other end of the tubing to a 250 ml flask containing limewater so that the end of the
tube is in the limewater.
g) Observe the difference in the appearance of lime water solutions in the beakers for each thermos.
Record your results under assignment 3 of the lab report.
Lime
water
Lime
water
Sucrose +
Yeast
Sucrose
Figure 7.8a – Control Thermos
Figure 7.8b – Experimental Thermos
Assignment 4 - A demonstration has been set up and will be discussed by your instructor.
Experiment to show the relationship between respiration and photosynthesis.
CO2 is produced via cellular respiration and that CO2 is used in photosynthesis. This experiment will
show you what happens to CO2 when photosynthesis is occurring and when it is not.
Procedure:
a) Place 15 drops of 0.004% bromthymol blue in to three test tubes numbered one through three
(1-3).
b) Take two leaves from a healthy plant. Do not allow the leaves to touch the liquid.
Keeping the surface of the leaves against the glass, roll and insert one leaf into tube 1 and
another leaf into tube 2.
c) Place nothing in tube 3.
d) Insert rubber stoppers into each tube.
e) Wrap tube 1 in aluminum foil to exclude light.
f) Place the tubes in a test tube rack and expose them to light, but not heat for 1 hour.
After one hour, note the color of the bromthymol solution in each tube. Record your results
under assignment 4 of the lab report.
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Lab Report - 7 Cellular Respiration
Anaerobic and Aerobic Metabolism
Name: ________________________________
Date:
____________________________
Class Index: ___________________________
Instructor: ____________________________
Before you begin filling out this lab report you must read Exercise 7 - Cellular Respiration in your lab
manual. Complete Assignments 1-8 below. You can use your Lab Manual results and Textbook to complete
the information below.
Assignment 1
To determine whether air exhaled from your lungs contains an accumulation of CO2
a. What was the color of Bromthymol blue solution before you exhaled into it? After you exhaled into it?
before ________________________________
After __________________________________
b. Why did the color of the Bromthymol blue change?
_______________________________________________________________________________
c. What is the source of CO2 in the exhaled human air?
________________________________________________________________________________
Assignment 2
Respiration and carbon dioxide production in germinating and dry seeds
Tube #
Amount of Material Used
1
6-10 Germinating Seeds
2
6-10 Dry Seeds
3
Nothing
Color of Bromthymol
Blue after test Interval
CO2 Concentration
(high/low)
a. Are dry seeds alive? (Yes/No) __________________. Support your answer.
_____________________________________________________________________________
_____________________________________________________________________________
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Assignment 3
Measuring the release of energy from sucrose.
a. Temperature in the control thermos _____0 C; Temperature in the experimental thermos _____ 0 C.
b. Which of the two types of fermentation has occurred? ___________________________________
c. What chemical substance is used to indicate the presence of CO2 gas?
_______________________________________________________
d. Is any indication of gas leaving the control thermos? _________ (Yes/No)
e. Is any indication of gas leaving the experimental thermos? _________(Yes/No)
How do you know? _________________________________________________________________
_________________________________________________________________________________
Assignment 4
Experiment to show the relationship between respiration and photosynthesis.
a. In test tube # 1 which gas is produced? What indicated the presence of that gas?
________________________________________________________________________________
________________________________________________________________________________
b. What was the purpose of wrapping the test tube # 1 with aluminum foil?
_________________________________________________________________________________
c. What can you say about the CO2 concentration in tubes#1 and #2? Explain the reason for the
difference?
Tubes#1 ________________________________
Ttubes#2_____________________________
__________________________________________________________________________________
__________________________________________________________________________________
d. What is the purpose of test tube #3
____________________________________________________________________________________
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