Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
Notes to Instructors
Chapter 9 Cellular Respiration: Harvesting Chemical Energy
Chapter 10 Photosynthesis
What is the focus of these activities?
In studying both cellular respiration and photosynthesis, many students tend to focus on
What are the particular activities designed to do?
Activity 9.1 A Quick Review of Energy Transformations
This activity adds consideration of the terms oxidation and reduction to the energy
relationships students learned in Chapter 8.
Activity 9.2 Modeling Cellular Respiration
Activity 9.2 is designed to help students understand:
Activity 10.1 Modeling Photosynthesis
Activity 10.2 How do C3, C4, and CAM photosynthesis compare?
Activities 10.1 and 10.2 are designed to help students understand:
• the roles photosystems I and II and the Calvin cycle play in photosynthesis, and
• how and why C4and CAM photosynthesis differ from C3photosynthesis.
What misconceptions or difficulties can these activities reveal?
Activity 9.1
This activity reviews the information presented in Chapter 8 and helps students integrate
into that an understanding of oxidation and reduction reactions that occur in living
organisms.
Notes to Instructors 43
Activity 9.2
By doing this modeling exercise, students will not only learn the definitions of all the
terms and structures involved in cellular respiration but also get an understanding of how
they function or interact in the cell.
Question 1: To help give students the “big picture,” this question looks at the summary
formula for cellular respiration and asks where each reactant is used and where each
product is produced in the process. Many students have difficulty answering most parts of
this question.
Questions 4, 5, and 6: These questions examine what happens in aerobic cellular
respiration when oxygen and, therefore, NAD+become limiting. We generally teach the
various processes of cellular respiration in order from glycolysis to the Krebs cycle to
electron transport and oxidative phosphorylation. Many students get the mistaken
impression that they must operate in this sort of relay fashion in the cell as well. Only a
few introductory students understand that all of these processes are occurring
simultaneously in the cell. Fewer yet have a good idea that various molecules and
resources in the cell (for example, NAD+) are finite and can be limiting. And it is the rare
student who can answer the question: Why does the Krebs cycle stop in the absence of
44 Notes to Instructors
Question 9: When chemiosmosis is discussed, students are asked to understand that a
hydrogen ion concentration gradient has potential energy that can be used to do work—in
this case, to drive the synthesis of ATP. The operation of a battery is often used as an
Question 12: This question asks why living organisms don’t spontaneously combust.
Students should be able to understand this if they understand the process of cellular
respiration.
Activity 10.1
Students have the same difficulties understanding photosynthesis that they have
understanding cellular respiration. This activity asks students to model photosynthesis in
Question 4: Whereas Activity 9.2 looked at what happens when NAD+becomes limiting
in cellular respiration, this question looks at what happens when NADP+becomes
limiting in photosynthesis.
Question 5: The question of why plants need to make glucose and store starch as an
energy source is addressed. Many students don’t understand why plants can’t just use the
ATP directly for processes other than photosynthesis. In fact, they can, as long as they are
Notes to Instructors 45
Activity 10.2
Question 1: This question is set up to allow students to more easily compare, and
therefore learn, the similarities and differences among C3, C4, and CAM photosynthesis.
Question 2: Many students have difficulty understanding how rubisco can serve as both a
Question 3: This question asks students to develop an evolutionary scheme for
glycolysis, the Krebs cycle, oxidative phosphorylation or electron transport, and
photosynthesis. Many students have the misconception that the order in which the
Answers
Activity 9.1 A Quick Review of Energy Transformations
Review Chapter 8 and pages 162–164 of Chapter 9 in Campbell Biology, 9th edition.
Then complete the discussion by supplying or choosing the appropriate terms.
To maintain life, organisms must be able to convert energy from one form to another. For
example, in the process of photosynthesis, algae, plants, and photosynthetic prokaryotes
use the energy from sunlight to convert carbon dioxide and water to glucose and oxygen
(a waste product).
The summary reaction for photosynthesis can be written as
46 Activity 9.1
The reactions involved in aerobic respiration are also redox reactions:
C6H12O6+ 6 O2→6 CO2+ 6 H2O
In this set of reactions, however, more complex molecules are “broken down” into
Spontaneous reactions rarely occur “spontaneously” because all chemical reactions, even
those that release energy, require some addition of energy—the energy of activation—
before they can occur. One way of supplying this energy is to add heat. An example is
heating a marshmallow over a flame or campfire. When enough heat is added to reach
(or overcome) the activation energy, the sugar in the marshmallow reacts by oxidizing.
(Burning is a form of oxidation.) The marshmallow will continue to burn even if you
remove it from the campfire. As the marshmallow burns, carbon dioxide and water are
formed as products of the reaction, and the energy that was stored in the bonds of the
sugar is released as heat.
Activity 9.1 47
Activity 9.2 Modeling cellular respiration: How can cells convert
the energy in glucose to ATP?
Using your textbook, lecture notes, and the materials available in class (or those you
devise at home), model both fermentation (an anaerobic process) and cellular respiration
(an aerobic process) as they occur in a plant or animal cell. Each model should include a
dynamic (working or active) representation of the events that occur in glycolysis.
Building the Model
• Use chalk on a tabletop or a marker on a large sheet of paper to draw the cell
membrane and the mitochondrial membranes.
Be sure your model of fermentation includes and explains the actions and roles of the
following:
48 Activity 9.2
glycolysis
cytoplasm
electrons
ADP
Pi
ATP
Be sure your model of cellular respiration includes and explains the actions and roles of
the following:
glucose electron transport chain
oxygen mitochondria
carbon dioxide inner mitochondrial membrane
pyruvate outer mitochondrial membrane
Use your models to answer the questions.
1. The summary formula for cellular respiration is
C6H12O6+ 6 O2→6 CO2+ 6 H2O + Energy
Activity 9.2 49
a. At what stage(s) in the
overall process is each of the
reactants used?
b. At what stage(s) in the overall process is each
of the products produced?
C6H12O6⫹6 O2→6 CO2⫹6 H2O⫹Energy
2. In cellular respiration, the oxidation of glucose is carried out in a controlled series of
reactions. At each step or reaction in the sequence, a small amount of the total
energy is released. Some of this energy is lost as heat. The rest is converted to other
forms that can be used by the cell to drive or fuel coupled endergonic reactions or to
make ATP.
50 Activity 9.2
a. What is/are the overall
function(s) of
glycolysis?
b. What is/are the overall
function(s) of the Krebs
cycle?
c. What is/are the overall
function(s) of oxidative
phosphorylation?
Oxidation of glucose to 2
Oxidation of
Oxidation of NADH and
3. Are the
compounds listed
here used or
produced in: Glycolysis?The Krebs cycle?
Oxidative
phosphorylation?
Glucose Used
4. The cell’s supply of ADP, Pi, and NAD+is finite (limited). What happens to cellular
respiration when all of the cell’s NAD+has been converted to NADH?
If NAD is unavailable, the cell is unable to conduct any processes that involve the
5. If the Krebs cycle does not require oxygen, why does cellular respiration stop after
glycolysis when no oxygen is present?
When no oxygen is present, oxidative phosphorylation cannot occur. As a result, the
6. Many organisms can withstand periods of oxygen debt (anaerobic conditions). Yeast
undergoing oxygen debt converts pyruvic acid to ethanol and carbon dioxide.
Animals undergoing oxygen debt convert pyruvic acid to lactic acid. Pyruvic acid is
fairly nontoxic in even high concentrations. Both ethanol and lactic acid are toxic in
even moderate concentrations. Explain why this conversion occurs in organisms.
As noted in question 4, when no NAD+is available, even glycolysis stops. No ATP
7. How efficient is fermentation? How efficient is cellular respiration? Remember that
efficiency is the amount of useful energy (as ATP) gained during the process divided
by the total amount of energy available in glucose. Use 686 kcal as the total energy
available in 1 mole of glucose and 8 kcal as the energy available in 1 mol of ATP.
Activity 9.2 51
Efficiency of fermentation Efficiency of aerobic respiration
8. a. Why can’t cells store large quantities of ATP? (Hint: Consider both the chemical
stability of the molecule and the cell’s osmotic potential.)
ATP is highly reactive at normal body temperatures and therefore difficult for cells to
b. Given that cells can’t store ATP for long periods of time, how do they store
c. What are the advantages of storing energy in these alternative forms?
These are very large molecules and, as a result, do not have as great an effect on
osmotic potential. They are also much more stable chemically than ATP.
9. To make a 5 Msolution of hydrochloric acid, we add 400 mL of 12.5 Mhydrochloric
acid to 600 mL of distilled water. Before we add the acid, however, we place the flask
containing the distilled water into the sink because this solution can heat up so rapidly
that the flask breaks. How is this reaction similar to what happens in chemiosmosis?
How is it different?
52 Activity 9.2
a. Similarities b. Differences
In both processes, as we add the acid to
Both processes set up a H+ion
9.2 Test Your Understanding
1. If it takes 1,000 g of glucose to grow 10 g of an anaerobic bacterium, how many
grams of glucose would it take to grow 10 g of that same bacterium if it was
respiring aerobically? Estimate your answer. For example, if it takes Xamount of
glucose to grow 10 g of anaerobic bacteria, what factor would you have to multiply
or divide Xby to grow 10 g of the same bacterium aerobically? Explain how you
arrived at your answer.
Aerobic respiration can produce a maximum of 38 ATP per glucose molecule.
2. Mitochondria isolated from liver cells can be used to study the rate of electron
transport in response to a variety of chemicals. The rate of electron transport is
measured as the rate of disappearance of O2from the solution using an oxygen-
sensitive electrode.
How can we justify using the disappearance of oxygen from the solution as a
measure of electron transport?
3. Humans oxidize glucose in the presence of oxygen. For each mole of glucose oxidized,
about 686 kcal of energy is released. This is true whether the mole of glucose is
oxidized in human cells or burned in the air. A calorie is the amount of energy required
to raise the temperature of 1 g of water by 1°C; 686 kcal ⫽686,000 calories. The
average human requires about 2,000 kcal of energy per day, which is equivalent to
about 3 mol of glucose per day. Given this, why don’t humans spontaneously combust?
As noted in question 9, during cellular respiration, the energy from the oxidation of
4. A gene has recently been identified that encodes for a protein that increases
longevity in mice. To function in increasing longevity, this gene requires a high ratio
of NAD+/NADH. Researchers have used this as evidence in support of a “caloric
restriction” hypothesis for longevity—that a decrease in total calorie intake increases
longevity. How does the requirement for a high NAD+/NADH ratio support the
caloric restriction hypothesis?
A decrease in calorie intake will decrease the rate of glycolysis and the Krebs cycle.
Activity 9.1 53
5. An active college-age athlete can burn more than 3,000 kcal/day in exercise).
a. If conversion of one mole of ATP to ADP + Pireleases about 7.3 kcal, roughly
speaking, how many moles of ATP need to be produced per day in order for this
energy need to be met?
b. If the molecular weight of ATP is 573, how much would the required ATP weigh
in kilograms?
c. Explain these results
Activity 10.1 Modeling photosynthesis: How can cells use the
sun’s energy to convert carbon dioxide and water into glucose?
Activity 10.1 is designed to help you understand:
1. The roles photosystems I and II and the Calvin cycle play in photosynthesis, and
2. How and why C4and CAM photosynthesis differ from C3photosynthesis.
Using your textbook, lecture notes, and the materials available in class (or those you
devise at home), model photosynthesis as it occurs in a plant cell.
Your model should be a dynamic (working or active) representation of the events
that occur in the various phases of C3photosynthesis.
Building the Model
• Use chalk on a tabletop or a marker on a large sheet of paper to draw the cell
membrane and the chloroplast membranes.
54 Activity 10.1
Your model of C3photosynthesis should include what occurs in photosystems I and II and
in the Calvin cycle. For photosystems I and II, be sure your model includes and explains
the roles of the following:
Also indicate where in the plant cell each item is required or produced.
For the Calvin cycle, be sure your model includes and explains the roles of the following:
glucose
C3or 3C sugars
carbon dioxide
NADPH
ATP
Also indicate where in the plant cell each item is required or produced.
Use your model and the information in Chapter 10 of Campbell Biology, 9th edition,
to answer the questions.
1. The various reactions in photosynthesis are spatially segregated from each other
within the chloroplast. Draw a simplified diagram of a chloroplast and include these
parts: outer membrane, grana, thylakoid, lumen, stroma/matrix.
a. Where in the chloroplast do the light
reactions occur?
In the thylakoid membranes
2. In photosynthesis, the reduction of carbon dioxide to form glucose is carried out in a
controlled series of reactions. In general, each step or reaction in the sequence
requires the input of energy. The sun is the ultimate source of this energy.
56 Activity 10.1
a. What is/are the overall
function(s) of
photosystem I?
b. What is/are the overall
function(s) of
photosystem II?
c. What is/are the overall
function(s) of the
Calvin cycle?
In noncyclic
photosphosphorylation,
Photosystem II generates
ATP. To fill the electron
The Calvin cycle uses the
ATP and NADPH
3. Are the compounds
listed here used or
produced in: Photosystem I? Photosystem II? The Calvin cycle?
Glucose Produced
O2Produced from the
breakdown of H2O
4. Which light reaction system (cyclic or noncyclic) would a chloroplast use in each
situation?
Activity 10.1 57
a. Plenty of light is available, but the
cell contains little NADP+.
b. There is plenty of light, and the cell
contains a high concentration of
NADP+.
If there is little NADP+, there must be
In this case, it appears that NADPH is
5. All living organisms require a constant supply of ATP to maintain life. If no light is
available, how can a plant make ATP?
Keep in mind that it is not always light and that not all cells of a plant are directly
Chloroplast thylakoids can be isolated and purified for biochemical experiments. Shown
below is an experiment in which pH was measured in a suspension of isolated thylakoids
before and after light illumination (first arrow). At the time indicated by the second arrow,
a chemical compound was added to the thylakoids. Examine these data and address the
following questions.
10.1 Test Your Understanding
a. Based on your understanding of the function of the chloroplasts, why does
turning on the light cause the pH in the solution outside the thylakoids to
increase?
Electron transfer (Photosystems II and I) in the thylakoid membrane resulted in
b. Given the response, the chemical added was probably an inhibitor of:
i. oxidative phosphorylation
ii. ATP synthase
iii. NADPH breakdown
iv. Electron transport chain between photosystems II and I
v. Rubisco
The answer is iv. Disrupting or inhibiting the electron transport chain between
Activity 10.2 How do C3, C4, and CAM photosynthesis
compare?
1. Carbon dioxide enters plant leaves through the stomata, while oxygen (the
photosynthetic waste product) and water from the leaves exit through the stomata.
Plants must constantly balance both water loss and energy gain (as photosynthesis).
This has led to the evolution of various modifications of C3photosynthesis.
58 Activity 10.2
8
6
pH
Light
time (minutes)
Chemical
e. What makes C4photosynthesis more efficient than C3photosynthesis in tropical
climates?
PEP carboxylase is much more efficient than rubisco at picking up CO2. As a
result, C4plants can capture large quantities of CO2and store it as a four-carbon
C3C4CAM
Draw simplified
diagrams of the
cross sections of a
leaf from a C3, a C4
and a CAM plant.
See Figure 10.4. See Figure 10.30.
CAM leaf anatomy
is similar to C3leaf
anatomy.
c. How and when
does carbon
dioxide get into
each leaf?
During daylight
hours, when
stomata are open
During cooler parts
of the day, when
stomata are open
At night, when it is
cool and stomata
are open
Activity 10.2 59
f. How is CAM photosynthesis advantageous in desert climates?
Stomata can be open at night when there is less evaporative loss of water and
2. Photosynthesis evolved very early in Earth’s history. Central to the evolution of
photosynthesis was the evolution of the enzyme rubisco (an abbreviation for ribulose
bisphosphate carboxylase oxidase). To the best of our knowledge, all photosynthetic
plants use rubisco. Rubisco’s function is to supply carbon dioxide to the Calvin
cycle; however, it does this only if the ratio of carbon dioxide to oxygen is relatively
high. (For comparison, a relatively high ratio of carbon dioxide to oxygen is 0.03%
carbon dioxide to 20% oxygen.) When the carbon-dioxide-to-oxygen ratio becomes
low, the role of rubisco switches and it catalyzes photorespiration, the breakdown of
glucose to carbon dioxide and water.
a. Why could we call photorespiration a “mistake” in the functioning of the cell?
Photorespiration could be called a “mistake” because under high O2/CO2
b. Rubisco is thought to have evolved when Earth had a reducing atmosphere. How
does this help explain the photorespiration “mistake?”
When the first photosynthetic organisms arose, the early Earth’s atmosphere
60 Activity 10.2
10.2 Test Your Understanding
The metabolic pathways of organisms living today evolved over a long period of time—
undoubtedly in a stepwise fashion because of their complexity. Put the following
processes in the order in which they might have evolved, and give a short explanation
for your arrangement.
First, glycolysis is found in all eukaryotes and many prokaryotes. It takes place in
the cytoplasm and can occur in the absence of oxygen.
Activity 10.2 61
