LAB 10. CELLULAR RESPIRATION: UNDERSTANDING CELLULAR RESPIRATION
Student learning outcomes
At the completion of this exercise, the student will be able to:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Define cellular respiration
Recite the equation for cellular respiration
Describe glycolysis, and tell where in the cell it occurs.
Define aerobic cellular respiration; include where in the cell the biochemical pathway
occurs and the products formed.
Define anaerobic cellular respiration.
Describe the two common fermentation pathways, and tell what products are formed in
each pathway.
Explain the function of the electron transport chain.
Compare the amount of ATP.
Describe the interrelationship between photosynthesis and cellular respiration.
OVERVIEW
Life is a conquest of energy that all begins with the sun. The radiant energy of sunlight is
converted into chemical energy (primarily glucose) through photosynthesis. In turn, the
glucose is used to produce adenosine triphosphate (ATP), the energy currency of living
systems, through the process of cellular respiration. Plants and animals have a unique
evolutionary relationship based upon each using the other’s products. As the results of
photosynthesis, some bacteria algae, and plants produce oxygen as a waste product. In turn,
the oxygen is a vital component in aerobic cellular respiration. The plants then use the CO2
produced in cellular respiration to ultimately build carbohydrate.
In nature, two major types of cellular respiration have evolved.
1. Some bacteria and fungi undergo anaerobic cellular respiration, which occurs in the
absence of oxygen. The ancestors of anaerobic organisms first appeared on Earth
approximately 3.5 billion years ago. Today, many species of anaerobic organisms
abound. Anaerobic bacteria can be found in certain soils, sediments in bodies of water
and the gut of some animals. Several species of anaerobic bacteria are responsible for
disease such gangrene, tetanus, and botulism.
2. Aerobic cellular respiration takes place in the presence of oxygen. The evolution of
aerobic cellular respiration began approximately 2.7 billion years ago, and the vast
majority of organisms on earth today are aerobic. The overall reaction of aerobic
cellular respiration is the reverse of photosynthesis.
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Anaerobic and aerobic respiration both begin with a molecule of glucose produced
through photosynthesis. With a few exceptions, the majority of living things undergo glucose
metabolism to release the energy from the sun locked within a molecule of glucose. The first step
in unlocking the energy within glucose is glycolysis. This complex pathway occurs anaerobically
in the cytoplasm of a cell. Because glycolysis is common to life on earth, it arose early in the
evolution of life.
The end products of glycolysis are four molecules of ATP (two of which are recycled in
further glycolysis), two molecules of NADH (nicotinamide adenine dinucleotide, a coenzyme),
and two molecules of pyruvate. If pyruvate is metabolized in the cytoplasm anaerobically, the
process is known as fermentation. If the pyruvate is shuttled into the mitochondrion, the process
continues aerobically and is known as aerobic cellular respiration.
Two significant types of fermentation reactions occur anaerobically: the alcoholic
fermentation reaction and lactate fermentation reaction. In both reaction, pyruvate is reduced by
NADH to form either ethyl alcohol (C2H5OH) or lactate ( C3H503). Both reaction produce two
molecule of water and only two molecules of ATP. Combined with the two ATPs produced from
glycolysis, the net yield of ATP during each reaction is only four molecules of ATP. Thus,
anaerobic organisms have no “energy to spare”. That explains why anaerobic life forms cannot
engage in a game of tennis or even “putt” around like a paramecium. Other types of
commercially important microbial fermentation process yield acetone and methanol.
AEROBIC CELLULAR RESPIRATION
One of the most significant events in the history of life was the evolution of aerobic
cellular respiration. In aerobic cellular respiration, the two molecules of pyruvate that result from
glycolysis are converted further to two molecules of acetyl coenzyme A and two molecules of
CO2 in a mitochondrion. This is the CO2 that you exhale. NAD+ facilitates the removal of
electrons from pyruvate and forms two molecules of NADH. The acetyl coenzyme (CoA) carries
the acetyl group.
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The acetyl group enters the citric acid cycle, or krebs cycle, named after the biochemist
Hans Krebs. The citric acid cycle is a complex series of metabolic reactions occurring in the
matrix of the mitochondrion. These reaction are enzymes-driven, and the products in one step of
the reaction become the reactants in the next. The end products of the citric acid cycle are two
molecules of ATP, four molecules of CO2, six molecules of NADH, and two molecules of
FADH2 (flavin adenine dinucleotide).
The final step of aerobic respiration occurs in the cristae of the mitochondrion and the
plasma membrane of prokaryotes. This process is known as the electron transport chain. At the
completion of the electron transport chain, typically 32 ATP molecules and water form. I the
electron transport chain, oxygen serve as the final electron acceptor by combining with two
hydrogen atoms to form water. The role of oxygen is responsible for the term aerobic cellular
respiration (Fig.11 .1)
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ALCOHOL FERMENTATION
Yeasts are unicellular organisms in kingdom Fungi that produce energy (ATP) anaerobically in a
two-step pathway called the alcoholic fermentation reaction (Fig. 11.2). In the first step of the
reaction, yeast chemically breaks down glucose into pyruvate in a series of metabolic reaction
called glycolysis. A molecule of carbon dioxide (CO2) is then removed from the pyruvic acid.
This leaves a two-carbon compound.
In second step of the reaction, two hydrogen atoms from NADH and H+ are added to the
two-carbon compound to form ethyl alcohol. The NADH is oxidized to form NAD+, an essential
molecule that allows the glycolysis pathway to continue.
Alcoholic fermentation is essential in making wine, beer, and bread. In making bred, the
CO2 produced causes the bread dough to rise. The ethyl alcohol evaporates during baking. Have
you ever eaten a slice of pizza or a piece of bread that smells a little of beer? The beer odor is a
bit of residual alcohol that has not completely evaporated!
A Tidbit from Biohistory
In the mid 1800’s, a French winery that produced alcohol from the fermentation of sugar beets
ran into a big problem: Its prized wine tasted like vinegar. The owner, Monsieur Bigo, contacted
the renowned Louis Pasteur to come up with a solution to the problem. At that time no one,
including Pasteur, really understood how sugar ferments into alcohol.
Pasteur sampled a healthy vat of fermenting sugar beets and, to his surprise, noted health
yeasts under the microscope. Next he examined a vat that contained poor-tasting wine. In this
vat, instead of finding yeasts, he observed rod-shaped bacteria. These bacteria were collected and
grown in a nutritive media. Pasteur determined that instead of producing alcohol as a byproduct,
the bacteria produced lactic acid. Thus, with this discovery, Pasteur was able to save the French
wine industry by ensuring that yeasts and not bacteria are introduced to wine-making vat.
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STUDENT ACTIVITY ALCOHOLIC FERMENTATION
Demonstrating alcoholic fermentation in yeasts
This activity has been designed to demonstrate alcoholic fermentation in yeasts (Fig. 11.3).
Materials:
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Half package of
yeast
25 mL 10%
glucose
Water
250 mL beaker
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Empty glass bottle
(Flask)
Stirring rod
Glass dropper
Microscope
Microscope slides
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Coverslips
Balloons
Hot plate
Thermometer
Rubber band
Procedure 11.1 Demonstrating Fermentation
1. Obtain the materials to be used in this
activity, and bring them to your lab
station.
2. Add 200 mL of tap water to the beaker,
and heat the water, using a hot plate, to
approximately 35 0C to 37 0C.
3. Carefully add the half package of yeast
and the 25 mL of 10 % glucose to the
water, and stir. Wash your hands after
handling the yeast.
4. Carefully pour the mixture into the glass
bottle to approximately the halfway
mark.
5. Cover the lip of the bottle with a
balloon, and secure the base of the
balloon to the bottle with a rubber band.
6. Observe and record what happens to the
balloon over the next 30 minutes.
7. Using a glass dropper, take a drop of the
mixture from the beaker
8. Make a wet mount of the mixture.
9. Observe the mixture using a microscope
on low and high power.
10. At the end of 30 minutes, remove the
balloon from the glass bottle, waft you
hand over the bottle, smell the contents
11. Clean your laboratory station,
glassware, and hands.
12. Return your materials to the designed
area.
13. Sketch your observations in the space
below.
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1. What happened to the balloon? Why?
____________
____________
2. Describe the odor of the mixture.
____________
____________
Cellular Respiration
The first law of thermodynamics state that energy cannot be created or destroyed, it only
changes from one form to another. Because living organisms have a constant energy
requirement, they have mechanisms to gather, store and use energy. Collectively these
mechanisms are called metabolism. A single, specific reaction that starts with one compound and
ends up with another compound is a reaction, and a sequence of such reactions is a metabolic
pathway.
In the last lab, you investigated the metabolic pathway by which green plants capture
light energy and use it to make carbohydrates such as glucose. Carbohydrates are temporary
energy stores. The process by which energy stored in carbohydrates is released to the cell is
respiration.
Both autotrophs and heterotrophs undergo respiration. Photoautotrophs such as plants
utilize the carbohydrates they have produced by photosynthesis to build new cells and maintain
cellular machinery. Heterotrophic organisms may obtain materials for respiration in two ways:
by digesting planting material of b digesting the tissue of animals that have previously digested
plants.
For aerobic respiration, the general equation is:
Enzymes
C6 H12 O6 + 6 O6
6 CO2
+
6 H2 O
+
36/38 ATP'S
If glucose is completely broken down to CO2 and H2O, about 686,000 calories of energy
are released. Each ATP molecule produced represents about 7,500 calories of usable energy. The
36 ATP represents 270,000 calories of energy (36 x 7,500 calories). Thus, aerobic respiration is
about 39% efficient [(270,000/686,000) x 100% =39.4%)
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Aerobic Respiration
During the process of aerobic respiration, relatively high-energy carbohydrates are broken down
in stepwise fashion, ultimately producing the low-energy products of carbon dioxide and water and
transferring released energy into ATP. But what is the role of oxygen?
During aerobic respiration, the carbohydrates undergo a series of oxidation-reduction reactions.
Whenever one substance is oxidized (loses electrons), another must be reduced (accept or gain, those
electrons). The final electron acceptor in aerobic respiration is oxygen. Tagging along with the electrons
as they pass through the electron transport process are protons (H+). When the electrons and protons are
captured by oxygen, water (H2O) is formed:
2H+
+
2e-
+
1/2 O2
→
H2O
In the following experiment, you will examine aerobic respiration in three sets of seeds.
Seeds contain stored food material, usually in the form of some type of carbohydrates. When a
seed germinates, the carbohydrate is broken down by aerobic respiration, liberating the energy (ATP)
required for each embryo to grow into a seedling. Two days ago, one set of dry pea seeds were soaked in
water to start the germination process. Another set was not soaked and another was boiled. In this
experiment, you will compare carbon dioxide production between germinating pea seeds, germinating pea
seeds that have been boiled and un-germinated (dry) pea seeds.
This experiment investigates the hypothesis that germinating seed produce carbon dioxide
(CO2) from aerobic respiration.
Materials
Per group
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3 Flasks (labeled germinating un-boiled, germinating-boiled, and un-germinated)
3 Large Test tube (fill with water)
3 Large Test tube(fill with phenol red)
Test tube rack
2 L plastic beaker or container (fill with tap water)
Procedure
1. Instructor will provide each group with germinating un-boiled, germinating-boiled, and
un-germinating seeds into the right flasks)
2. As soon as the instructors provide you with the seeds insert the large rubber stopper into
the flask. (Be sure that both the small and the large rubber stopper are placed correctly, so
no air can enter the flasks)
3. Insert the glass tubing inside the large test tube that is filled with water as shown in the
figure below. (This keeps gases from escaping from the flask).
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4. Set the three respiratory flask apparatus aside for 1 ½ hours (90 minutes).
5. Make a prediction about carbon dioxide production in each respiratory flask apparatus on
Table 11.1.
Table 11. Prediction of Pea seeds
Germinating- unboiled
Germinating-boiled
Ungerminated
6. After 1 ½ hours (90 minutes), replace the test tube that are filled with water, with the test
tubes filled with phenol red.
Phenol red solution, which should appear pinkish in the stock in the stock bottle, will be used
to test for the presence of carbon dioxide (CO2) within the respiration bottle. If CO2 is
bubbled through water, carbonic acid (H2CO3) forms:
CO2
+
H2O
→
H2CO3
Phenol red solution is mostly water. When the phenol red solution is basic (pH>7), it is pink;
when it is acidic (pH<7) the solution is yellow. The phenol red solution in the stock bottle is
_______________ (color); therefore, the stock solution is
_______________ (acidic/basic)
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7. Remove the small rubber stopper on the top of the thistle tube and slowly pour water
from the bucket into each thistle tube. (The water will force out gases present in the
bottles. If CO2 is present, the phenol red will turn yellow.
8. Record your observation on Table 11.2.
Table 11.2 Pea seeds results
Pea seeds
Phenols red color
(pink or yellow)
Conclusion
(CO2 present or absent)
Germinating- unboiled
Germinating-boiled
Ungerminated
1. Which set(s) of seeds underwent respiration? Why? _____________________________
________________________________________________________________________
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2. What happened during boiling that caused the germinating boiled seeds to get the results
you found?
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________________________________________________________________________
3. Write a conclusion, accepting or rejecting the hypothesis. ________________________
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___________________________________________
Last Name, First Name [lab partner N0. 1]
____________________________________________
Last Name, First Name [lab partner N0. 2]
_______________________________
_______________________________
Last Name, First Name [lab
partner N0. 3]
___________________________
Section
Last Name, First Name [lab
_______________
group #
partner N0. 4]
____________________
Date
Review Questions Lab 10: Cellular Respiration: Understanding
Cellular Respiration
1. What is the overall equation for aerobic respiration?
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2. What are the origins of the reactants and the destiny of products?
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3. Compare and contrast anaerobic respiration. Include an account of the number of ATP
molecules Produced in each reaction.
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4. What is the interrelationship between photosynthesis and cellular respiration?
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5. Why do many scientists consider one of the most important events in the evolution of life to
be the origin of aerobic respiration?
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6. Compare and contrast alcoholic fermentation and lactate fermentation?
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7. What are three products of alcoholic fermentation and lactate fermentation?
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8. What is the significance of glycolysis?
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9. Outline the series of events that occur once pyruvate is committed to the aerobic pathway?
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10. How many ATP molecules are produced in the citric acid cycles?
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11. What is the significance of the electron transport chain?
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12. What are the end products of the electron transport chain?
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13. What is the role of oxygen in the electron transport chain?
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14. Why are more life forms on the earth intimately linked to a star that is 150 million Km away?
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