Cellular Respiration

How is energy transferred and transformed in living systems?

Why?- Living organisms display the property of metabolism, which is a general term to describe the
processes carried out to acquire and use energy. We know that people need to eat, and in our foods are
various kinds of nutrients that our cells use. One large group of nutrients in our foods is carbohydrates,
which supply our cells with glucose (C6H12O6). So the question is: How does the food we chew and
swallow fuel our cells?
Model 1 – Glycolysis

Cell membrane

NAD NADH

ADP ATP

NAD ! = pyruvic acid (3 C) ATP NADH

ADP
= glucose (6 C )
= mitochondrion

= nucleus

1. Refer to Model 1.
a. What is represented by the hexagon Glucose
b. and how many carbon atoms (C) are in one molecule of glucose? Six
2. Refer to Model 1.
a. What is represented by the triangle, Pyruvic acid
b. and how many carbon atoms (C) are in one molecule of pyruvic acid? Three
3. In the process of glycolysis, what happens to glucose after it crosses the cell membrane into the
cytoplasm of the cell?
Glucose is broken down into pyruvic acid
Read This! Glycolysis occurs in the cytoplasm of cells and does not require the presence of oxygen.
Therefore, the process is anaerobic. It is the first step used by cells to extract energy from glucose in the
form of ATP. ATP can be directly used by cells.

4. Thinking about the number of carbon atoms in glucose and in pyruvic acid, explain why there is
one molecule of glucose on the left side of the arrow and two molecules of pyruvic acid on the right
side of the arrow.

5. How many ATP molecules are produced during glycolysis?

two

Cellular Respiration 1
 6. Does glycolysis occur inside or outside the mitochondria?
Outside

Model 2 – Krebs Cycle

Mitochondrial matrix Inner
mitochondrial
membrane

NAD+ FAD NADH FADH2

NAD+ NADH

NAD+ NAD+ NADH

ADP NADH ATP
= pyruvic acid (3 C)
Outer mitochondrial
= carbon dioxide (1 C)
membrane

7. According to Model 2, what happens to pyruvic acid during the Krebs cycle?
It is broken down into three molecules of co2
8. According to Model 2, where does the change identified in the previous question occur?
In the mitochondrial matrix
9. Note the number of atoms of carbon in pyruvic acid and explain why three molecules of carbon
dioxide are produced.
Each pyruvic acid molecule contains three carbon atoms and each carbon dioxide molecule contain.

10. Considering that glycolysis produces two pyruvic acid molecules per glucose molecule, how
many total CO2 molecules will be produced from the complete breakdown of each glucose
molecule? Show a mathematical equation to support your answer.
Six, Each pyruvic acid has three carbons and two pyruvic acid molecules are produced
11. What two hydrogen-carrying molecules are formed during the Krebs cycle?

Nadh and fadh

12. Fill out the chart by looking back at the entire process of glycolysis and the Krebs cycle to list the
total number of ATPs and hydrogen-carrying molecules produced.
Process ATP NADH FADH2
2 2 0
Glycolysis

Krebs cycle 1 4 1
(1st pyruvic acid)

Krebs cycle 1 4 1
(2nd pyruvic acid)

2 POGIL™ Activities for High School Biology

Model 3 – The Electron Transport Chain

Outer mitochondrial
membrane
H+ H+ H+

e– = electron
= oxygen
Mitochondrial
matrix
e–
ADP ATP
NADH NAD +
e– H+
Inner mitochondrial
membrane FADH 2 FAD H2 O

13. What cell structure is the site for the electron transport chain?
The inner mitochondrial membrane
14. Label the carrier proteins in Model 3.
15. What substance do the carrier proteins transport across the inner mitochondrial membrane?
Hydrogen ions
Read This! 
NADH and FADH2 molecules release hydrogen ions that are transported across the inner mitochondrial
membrane with the help of electrons. The result of these multiple processes is the production of large
amounts of ATP.

16. What high energy molecules are formed by the electron transport chain?
Atp
17. Refer to Model 3.
a. What atom accepts the hydrogen ion at the end of the electron transport chain?
Oxygen accepts the hydrogen ions
18. Formulate an explanation for why the events of the electron transport chain constitute (uses) an
aerobic process rather than an anaerobic process (like glycolysis).’
The electron transport chain is an aerbioc process because it requires oxygen to complete the
process.

Read This!  Remember that glycolysis produces two pyruvic acid molecules per glucose molecule
along with two of the hydrogen-carrying NADH molecules. Remember also that the Krebs cycle produces
NADH as well as another hydrogen carrier called FADH 2. It is important to know that during the electron

Cellular Respiration 3
transport chain, when each NADH gives up electrons and hydrogen ions, there is enough of a potential
energy change to make three ATP molecules. When each FADH 2 gives up electrons and hydrogen ions,
there is enough of a potential energy change to make two ATP molecules.

19. Fill in the chart below to calculate the total amount of ATP produced from the breakdown of each
glucose molecule during the three steps of cellular respiration.
Number of H-carriers
Number of ATP produced from one glucose
produced from one molecule
glucose molecule NADH FADH2

Glycolysis 2 2 0

Krebs Cycle 2 8 2

Electron Transport Chain _______________ x3 x2

Total ATP Produced 4 30 4

Grand Total ATP produced (add all 3 columns above) 38

20. Look at the equation for cellular respiration and write in which stage of the process each molecule
is either used or produced.

C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP

Used in Used in Produced Produced Produced
in in in
Glycolysis Electron Kerb cycle Electron Glycolysis 2
transport transport
Kerb 2
chain chain
E.T.C 34

21. Compare the ATP available to cells when oxygen is present versus when it is absent. How might
this help explain why brain and heart functions are so quickly affected when a person cannot
breathe?

4 POGIL™ Activities for High School Biology