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Chapter 9 Cellular Respiration-ANSWERS
9.1 Catabolic pathways oxidize organic fuels____________________________________
1.Where does the energy stored in organic molecules originally come from?
Sun
2. Describe the flow of energy through an ecosystem. Starting with The energy souce you
identified in the previous question.
Sun Light energy  autotrophs make glucose=chemical energy)  herbivores use
glucose to make ATP=another chemical energy when organisms use chemical energy
some energy is always lost as Heat Energy during the transformation.
3. Write the equation for the catabolism (breakdown) of glucose.
A. What are the Reactants?
B. What are the Products?
C. Is the reaction exergonic or endergonic?
A. Reactants glucose and oxygen
B. Products carbon dioxide and water
C. Exergonic because energy is released when hydrogen atoms are removed from glucose
by the dehydrogenase enzyme.
4. In a redox reaction, the loss of electrons from one substance is called (oxidation or
reduction), and the addition of electrons to another substance is called (oxidation or
reduction). Remember…LEO (Lose Electrons Oxidation) the tiger says GER (Gain
Electrons Reduction)
5. Which reactant is oxidized and which is reduced in the equation for catabolisim
(breakdown) of glucose?
Electrons are taken away from glucose, so glucose is oxidized.
Electrons are added to Oxygen in the last step of cell respiration, so it is reduced.
6. During Cellular respiration, glucose is not catabolized (broken down) in a single step.
WHY?
So that the energy stored in the bonds of glucose can be harnessed to make ATP. If all
electrons were transferred to oxygen in one step very little energy would be captured to
make ATP.
7. A.. What enzyme pulls the hydrogen atoms from glucose and transfers them to the
coenzyme? Dehydrogenase
B. To what coenzyme are the hydrogen atoms ( a hydrogen atom is made of 1electron
and 1proton) transferred after being stripped from glucose? NAD+
C. How many electron(s) and proton(s) does this enzyme transfer to the coenzyme
identified in the previous question? Two electrons, One proton
D. After the enzyme transfers the appropriate number of electrons and protons to the
coenzyme the coenzyme becomes NADH. Explain this transformation in terms of the
number of electrons and protons transferred.
Coenzyme NAD+  NADH
-If we add 1 electron to NAD+ we get NAD. The electron has a negative charge, so it
neutralizes the positive charge on NAD+
-To convert NAD to NADH, we need to add a hydrogen atom (H). A hydrogen atom is
made of 1 electron and 1 proton.
-In summary we have added 1 electron to convert NAD+ to NAD and 1 more electron
and one proton to convert NAD to NADH!
E. Using your answers for the previous questions A-D, explain why NADH is called an
“electron carrier”.
NADH will carry electrons pulled from glucose to the final step of cell respiration where
their energy will be used to power the production of ATP.
9.2 Glycolysis____________________________________________________________
8. Where does glycolysis occur?
In the cytpplasm of the cell.
9. The word gylcolysis means “splitting sugar.”
A) What sugar is split? Glucose
B) What is this sugar split into (i.e. the end products of glycolysis?)
2 pyruvate molecules
10A.Why is the first part of glycolysis called the energy investment phase?
2 molecules of ATP are USED to complete the first half of the glycolysis reactions.
10B.Why is the second part of glycolysis called the energy payoff phase?
4 molecules of ATP are MADE to complete the other half of the glycolysis reactions.
10C. How many NET ATP are produced during one round of glycolysis?
Net 2ATP are produced. You used 2 ATP in the energy investment. Then you made 4
ATP in the energy payoff phase, so you have an overall total (net) of 2 ATP at the end of
glycolysis.
11.List the major products of glycolysis.
Pyruvate
ATP
NADH
12. Of the products listed in the previous question, which is the most important product
produced? EXPLAIN why it is the most important.
Pyruvate.
Pyruvate it is the major reactant for the next stage of cell respiration, the Krebs
cycle/citric acid cycle. Without pyruvate the krebs/citric acid cycle will have no starting
material and will not produce product. Without the major product of the citric acid cycle,
the third and final step of cell respiration (where NEARLY ALL the ATP is made) will
have not have enough stating material to produce its major product (ATP).
9.3 Krebs/Citric Acid Cycle (CAC)__________________________________________
13. Where does the Krebs/Citric acid cycle occur?
In the matrix (innermost space) of mitochondria.
14. Identify the major reactant for the Krebs/Citric Acid Cycle.
Pyruvate (made in glycolysis)
This is more info thatn you need to know for this course but just so you know….
…Pyruvate loses CO2 before entering the mitochondrial matrix and is converted into
Acetyl CoA, which initiates the citric acid cycle. So Acetyl CoA is the actual starting
material for the CAC, but it cannot be made without pyruvate, so this is why we say
pyruvate is the major reactant
15. List the major products of the CAC.
CO2 (this is the gas you exhale! It also happens to be one of the major reactants for
photosynthesis!)
ATP (just a little bit)
NADH
FADH2
16. Of the products listed in the previous question, which is the most important product
produced? EXPLAIN why it is the most important.
NADH/FADH2
NADH/FADH2 are the major reactants for the next stage of cell respiration, oxidative
phsophorylation. Without NADH2 will have no starting material and will not produce
product. Without the major product of the citric acid cycle, the third and final step of cell
respiration (where NEARLY ALL the ATP is made) will have not have enough stating
material to produce its major product (ATP).
17. Where are the NADH molecules that are produced in the CAC eventually used?
Electron transport chain (ETC) during Oxidative Phosphorylation. They give the
electrons they are carrying (that originally came from the bonds of glucose) to the protein
pumps of the ETC. The electrons give the protein pumps energy to pump ions across the
innermembrane of the mitochondria to the intermembrane space.
18. FADH2 looks very similar to another product of the CAC. What other product of the
CAC is it similar to and what is this molecule’s function in cell respiration? It is very
similar to NADH, as it is also an electron carrier. It drops its electrons off at the electron
transport chain further down the chain than NADH because it is a lower energy electron
carrier.
9.4 Oxidative phosphorylation (OP)___________________________________________
19. Where does Oxidative Phosphorylation (OP) take place? Identify the major organelle
and any membranes or spaces within that organelle.
In general, OP takes place in the mitochondria, but you need to know more details about
where exactly in the mitochondria to understand OP.
Important membrane of the mitochondria for OP:
Inner membrane
The inner membrane of the mitochondria had many electron transport chains (ETC)
embedded in its phospholipid bilayer. The ETC is made up of protein pumps and electron
transporters.
Important spaces of the mitochondria for OP:
Matrix and Intermembrane Space
Protons also called Hydrogen ions (positive ions, often represented as + or H+) are
pumped through the protein pumps of the ETC from the Matrix to the Intermemebrane
Space of the mitochondria. H+ are concentrated in the Intermembrane space, producing a
gradient (more H+ in the intermembrane space, less H+ in the matrix).
20A. What are the major reactants of OP?
NADH and FADH2
Oxygen
Hydrogen ions (H+), AKA: protons
20B. NADH and FADH2 is one of the major reactants for OP. What part of these major
reactants is being used by the ETC? (HINT: What are they carrying?)
The Electrons they carry (remember, these electrons were pulled from glucose) are given
to the electron transport chain protein pumps.
20C. Describe how the major reactants identified in the previous question are used by the
ETC.
The energy from the electrons is transferred to the protein pumps of the ECT. The pumps
use this energy to pump Hydrogen ions (H+) from lower concentration of Hydrogen ions
in the mitochondrial matrix to higher concentration of Hydrogen ions in the
Intermembrane space. The ETC protein pumps are pumping H+ from low to high. This
requires ENERGY. Where does this energy to pump H+ from low to high concentration
across the innermembrane of the mitochondria come from …the electrons!
20D. What (reactant molecule) causes the electrons to move from one part of the ETC to
the next?
Oxygen (in the air you breathe, one of the major reactants of cell respiration) is very
electronegative (this means it LOVES electrons and wants them more than other atoms)
pulls, so to speak, electrons through the ETC from one part of the chain to the next until it
grabs them at the very last protein of the ETC. The oxygen with these electrons then
combines with H+ ions to create water…water is one of the major products of this
process.
21. As a result of electron transfer from one protein of the electron transport chain to the
next, ___Protons H+______(ions) are actively transported from the matrix of the
mitochondria to the intermembrane space.
Why does the transport of the ions identified above require energy?
There is a lower concentration of Hydrogen ions (H+) in the mitochondrial matrix and a
higher concentration of Hydrogen ions (H+) in the Intermembrane space. The ETC
protein pumps are pumping H+ from low to high. This requires ENERGY. Think of it as
rolling a ball up a hill (low to high) vs. down a hill (high to low). Which one requires an
input of energy. UPHILL (low to high)!
22A.The gradient of H+ ions (AKA: protons) in the intermembrane space (created by the
electron transport chain) is called the proton motive force.
Can H+ ions diffuse from the intermembrane space to the matrix through…
i. ETC protein pumps? EXPLAIN why or why not.
ii. phospholipid bilayer of the inner membrane? EXPLAIN why or why not.
iii. ATPsynthase? EXPLAIN why or why not?
H+ ions can move down their gradient (high to low) back into the matrix from the
intermembrane space only by going through the ATPsynthase.
IMPORTANT: H+ ions cannot move back through the proteins of the ETC (these are a
one way street, from matrix to intermembrane space only) or through the phospholipid
bilayer of the inner membrane of the mitochondria (because H+ are charged, polar
molecules and the membrane in mainly nonpolar (see chapter 7).
22B. Describe how the mitochondria uses the gradient of H+ ions/proton motive force to
produce ATP. (HINT: discuss the ATP synthase)
As H+ ions diffuse through the ATP synthase down their concentration gradient from
(high to low.) This results in conformational changes that open up catalytic sites on the
ATP synthase where ADP is joined to Phosphate to make ATP.
23. What are the major products of OP?
ATP
NAD+
Water
24. What product of OP is most important (purpose of Cell respiration)?
ATP
25. Summarize the travel of an electron through cellular respiration starting with an
electron that is pulled from a glucose molecule in the cytoplasm and ending with the
electron associating with oxygen in the last stage of cell respiration:
Food NAD+  NADH electron transport chain proteins oxygen
26. SUMMARY OF 3 MAJOR STEPS OF CELL RESPIRATION:
a. Most important molecule
produced in glycolysis
b. Most important
molecule produced in
the Krebs cycle?
c. Most important molecule
produced in oxidative
phosphorylation?
PYRUVATE
NADH AND FADH2
ATP
Are the compounds
listed here used,
produced or neither
(N/A) in:
Glucose
Glycolysis?
USED
The Krebs cycle?
Oxidative
phosphorylation?
N/A
N/A
N/A
USED
PRODUCED
N/A
N/A
PRODUCED
USED AND
PRODUCED
PRODUCED
PRODUCED
USED AND
PRODUCED
USED
USED
NADH
PRODUCED
PRODUCED
USED
NAD
USED
USED
PRODUCED
N/A
O2
CO2
N/A
H2O
N/A
ATP
ADP  P
i
9.5 Fermentation________________________________________________________
27. Where does fermentation occur? Cytoplasm of the cell.
28A. What metabolic step do Cellular respiration and Fermentation have in common?
Glycolysis - no Oxygen required
28B. In terms of reactants, what is the major difference between fermentation and cell
respiration?
Fermentation does not require oxygen
Cell Respiration requires oxygen
29.Which process, fermentation or cell respiration produces more ATP?
Cell Resp.
What are the approximate numbers of ATP produced in each process per glucose
molecule?
~36-38 ATP made in Cell Respiration vs. 2 ATP in Fermentation
30.Why do scientists think glycolysis preceded the full process of cellular respiration in
evolution as a process to make ATP? Early atmosphere had little oxygen, so organisms
had to produce ATP without oxygen. When Oxygen became more abundant with rise of
photosynthetic plants, process of cell respiration was created as a more lucrative way to
make energy
9.6_____________________________________________________________________
31.T/F Glucose is the only organic molecule that can be utilized during cellular
respiration to make ATP. Fats and proteins can also be used. See fig. 9.19
32. Cellular respiration is controlled by an allosteric enzyme Phosphofructokinase at a
key points in glycolysis (see figure below). Explain how Phosphofructokinase regulates
the rate of respiration in the cell when…
A. ATP increases
When cell has made enough ATP, ATP acts as an inhibitor and will inhibit the
phosphofructokinase enzyme by stabilizing the inactive form of this allosteric enzyme,
which will stop gylcolysis and any cell respiration events that follow.
B. ATP decreases
When ATP is low in cell, ATP will no longer inhibit the phsophfructokinase enzyme,
allowing gylcolysis, citric acid cycle and oxidative phosphorylation to proceed and make
the necessary ATP.