Biology & Life Sciences Chapter 9-10 Homework Before Add The Acid However Place The

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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

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

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