Section 1 Energy and Living · PDF file94 Chapter 5 • Photosynthesis and Cellular...

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section is a broadoverview of energy flow in naturalsystems. It also serves as an intro-duction to the process that convertsfood into ATP.

Ask students to list as many differ-ent forms of energy as they can.(Answers will vary but should includeheat, light, chemical energy, mechani-cal energy, and electrical energy.)

ActivitySandwich Energy Have studentstrace the energy in a ham andcheese sandwich back to the sun.(Ham ➠ pig ➠ grains ➠ sun. Cheese➠ milk ➠ cow ➠ grass ➠ sun. Bread➠ wheat ➠ sun. )

Logical

Teaching TipDeep-Sea Vents Explain that thevast majority of autotrophs arephotosynthetic, and include plants,prokaryotes, and algae. Thechemoautotrophs are prokaryotes,many of which live around deep-sea volcanic vents in completedarkness. Have students researchdeep-sea vents and some of theorganisms that are supported bythese unique autotrophs. TAKS 2 Bio 4B; Bio 9B

TeachTeach

TAKS 2 Bio 4B; Bio 9CLS

GENERAL

MotivateMotivate

Bellringer

FocusFocus

Trends in Fuel Production Food Energy Sometimes food is burned forenergy. For years, grain has been fermented tomake ethanol, an alcohol that can be added togasoline to boost power and reduce pollution.New research is producing fuels based entirelyon renewable sources. These fuels can be madefrom grains such as corn and wheat, or evenfrom trees and grasses. Biodiesel is a diesel-likefuel made from vegetable oil. TAKS 5 IPC 6D (grade 11 only); IPC 8E

Section 1

94 Chapter 5 • Photosynthesis and Cellular Respiration

• Lesson Plan • Directed Reading• Active Reading GENERAL

GENERAL

Chapter Resource File

• Reading Organizers• Reading Strategies

Planner CD-ROM

Section 1 Energy and Living Things

Energy in Living SystemsYou get energy from the food you eat. Where does the energy in foodcome from? Directly or indirectly, almost all of the energy in livingsystems needed for metabolism comes from the sun. Figure 1 showshow energy flows through living systems. Energy from the sunenters living systems when plants, algae, and certain prokaryotesabsorb sunlight. Some of the energy in sunlight is captured andused to make organic compounds. These organic compounds storechemical energy and can serve as food for organisms.

Building Molecules That Store EnergyMetabolism involves either using energy to build molecules orbreaking down molecules in which energy is stored. is the process by which light energy is converted to chemical energy.Organisms that use energy from sunlight or from chemical bonds ininorganic substances to make organic compounds are called

(AWT oh trohfs). Most autotrophs, especially plants, arephotosynthetic organisms. Some autotrophs, including certainprokaryotes, use chemical energy from inorganic substances tomake organic compounds. Prokaryotes found near deep-sea vol-canic vents live in perpetual darkness. Sunlight does not reach thebottom of the ocean. These prokaryotes get energy, however, fromchemicals flowing out of the vents.

autotrophs

Photosynthesis

Objectives● Analyze the flow of energy

through living systems.

● Compare the metabolism of autotrophs with that ofheterotrophs.

● Describe the role of ATP inmetabolism.

● Describe how energy isreleased from ATP.

Key Terms

photosynthesisautotrophheterotrophcellular respiration

1. Plants convert light energy to chemical energy.

2. Rabbits get energy by eating plants.

3. Foxes get energy by eating rabbits.

Light energy

Energy flows from sunlight or inorganic substances to autotrophs, such asgrasses, and then to heterotrophs, such as rabbits and foxes.

Figure 1 Flow of energy

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9D

4B

4B

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Student Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9D TEKS Bio 4B, 9D

Teacher Edition TAKS Obj 2 Bio 4BTAKS Obj 3 Bio 9DTAKS Obj 5 IPC 6DTEKS Bio 4B, 9B, 9C, 9D, 12A, 12ETEKS IPC 6D, 8E

pp. 94–95

TAKS 3

TAKS 2

TAKS 2

Vocabulary Have students use adictionary to define the root wordsof autotroph and heterotroph.(auto � self; hetero � other; troph �nutrition or feeding; so an autotrophis literally “self-feeding,” and a het-erotroph is literally “other-feeding.”)

Verbal

Using the FigureAsk students to identify theautotrophs (grasses) and het-erotrophs (rabbits, fox) in Figure 1.Next, ask students how the fox isindirectly using the sun to getenergy. (The plants convert theenergy in sunlight to chemical energystored in plant tissues. Rabbits eatthe plants to get the stored chemicalenergy. The fox then eats the rabbit.

Visual

Teaching TipAutotrophs versus HeterotrophsMake two columns on the boardwith the heads autotroph andheterotroph. Ask each student toname one specific autotroph andone specific heterotroph. Write thestudent’s responses in the columns.If you notice a pattern—such asstudents naming mostly mammals—bring this to their attention. Tellthem other kinds of heterotrophsexist, such as some protists andfungi. Bio 9BCo-op Learning

GENERAL

TAKS 3 Bio 9D; Bio 12A, 12ELS

GENERAL

LS

SKILLBUILDER

READINGREADING

Chapter 5 • Photosynthesis and Cellular Respiration 95

MISCONCEPTION ALERT

Transfer of Energy Because ATP suppliesmost of the energy that drives metabolism,ATP is sometimes called an energy-rich com-pound, and the bonds between its phosphategroups are sometimes called “high-energy”bonds. These terms are misleading becausethey imply that ATP contains an unusually

large amount of energy. ATP serves as thecell’s energy currency. The bonds betweenphosphate groups are unstable and thereforebreak easily. When they break, energy isreleased that can be use to drive metabolicprocesses.

• Unit 2 PhotosynthesisThis engaging tutorial gives studentsan overview of photosynthesis.

• Unit 3 Cellular RespirationThis engaging tutorial reviews theprocess of cellular respiration.

BIOLOGYBIOLOGY

Transparencies

TT BellringerTT Breakdown of StarchTT ATP Releases Energy

Breaking Down Food for EnergyThe chemical energy in organic compounds can be transferred toother organic compounds or to organisms that consume food.Organisms that must get energy from food instead of directly fromsunlight or inorganic substances are called (HEHT uhroh trohfs). Heterotrophs, including humans, get energy from foodthrough the process of cellular respiration. is ametabolic process similar to burning fuel. While burning convertsalmost all of the energy in a fuel to heat, cellular respiration releasesmuch of the energy in food to make ATP. This ATP provides cellswith the energy they need to carry out the activities of life.

Transfer of Energy to ATPThe word burn is often used to describe how cells get energy fromfood. Although the overall processes are similar, the “burning” offood in living cells clearly differs from the burning of a log in acampfire. When a log burns, the energy stored in wood is releasedquickly as heat and light. But in cells, chemical energy stored infood molecules is released gradually in a series of enzyme-assistedchemical reactions. As shown in Figure 2, the product of onechemical reaction becomes a reactant in the next reaction. In thebreakdown of starch, for example, each reaction releases energy.

When cells break down food molecules, some of the energy in themolecules is released as heat. Much of the remaining energy isstored temporarily in molecules of ATP. Like money, ATP is aportable form of energy “currency” inside cells. ATP delivers energywherever energy is needed in a cell. The energy released from ATPcan be used to power other chemical reactions, such as those thatbuild molecules. In cells, most chemical reactions require lessenergy than is released from ATP. Therefore, enough energy isreleased from ATP to drive most of a cell’s activities.

Cellular respiration

heterotrophs

C O

C C

CCHOH H

H OH

CH2OH

H

OH

OH

H

6CO2 + 6H2O

Carbondioxide

ProductsReactant

ProductReactant

Starch

Glucose

EnzymesEnzyme

Water

ATP

Heat

Energy is released from starch in a series of enzyme-assisted chemical reactions.

Figure 2 Breakdown of starch

The words autotroph andheterotroph have the samesuffix, -troph, which is fromthe Greek word trophikos,meaning “to feed.” The pre-fix auto- is from the Greekword autos, meaning “self,”and the prefix hetero- isfrom the Greek wordheteros, meaning “other.”

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Group ActivityFlow of Energy Assign studentsto cooperative groups of three orfour. Have each group create a dis-play that shows the transfer ofenergy through living systems.

Interpersonal TAKS 3 Bio 9D, 12E;Bio 9D; IPC 8B

ReteachingSet up a demonstration thatincludes several organisms, such asa sponge, a worm, a Venus flytrap,and a mushroom. Have studentsexamine the display. Do not letthem touch any of the items. Askstudents to decide which itemsrepresent heterotrophs and whichrepresent autotrophs. Visual

Quiz1. Organisms that can make their

own food using the energy of thesun are called ________.(autotrophs)

2. Organisms that obtain theirenergy by eating other organismsare called ________. (heterotrophs)

AlternativeAssessmentHave students build a three-dimensional model of ATP(adenosine triphosphate). Studentsshould use everyday materials, andinclude the three phosphate groups,the sugar, and the base. Make surestudents understand which part ofthe nucleotide breaks off to giveenergy for cellular reactions. (thelast phosphate group) KinestheticBio 3E, 9A, 9B; IPC 8B

LS

Bio 12B

TAKS 3 Bio 12B

GENERAL

LS

CloseClose

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Teach, continuedTeach, continued

Answers to Section Review

1. the sun 2. Autotrophs use the energy in sunlight or inor-

ganic substances to make organic compounds.Heterotrophs must consume food sources toget energy needed to power their metabolism.

3. When the outer phosphate bond in a moleculeof ATP is broken, energy is released.

4. Fox eat other organisms to get the energyneeded for their metabolism. The animals theyeat acquired their energy from eating plants.The plants used the energy of the sun to con-vert compounds into carbohydrates, whichpower their metabolism. Thus, foxes get theirenergy indirectly from the sun. TAKS 3 Bio 9D

TAKS 2 Bio 4B

Bio 9B

TAKS 3 Bio 9D 5. The flow of energy between organisms is con-tinuous because energy passes from the sun toautotrophs, then to heterotrophs, and then toother heterotrophs.

6. A. Incorrect. The snake obtainsenergy by eating the grasshopper. B. Incorrect.The grasshopper obtains energy by eatinggrass. C. Incorrect. Grass produces carbohy-drates by using energy from the sun. D.

Correct. The original energy source for thehawk is the sun. TAKS 3 Bio 12E

TAKS 3 Bio 9D


ATPRecall that ATP (adenosine triphosphate) is a nucleotide with twoextra energy-storing phosphate groups. As shown in Figure 3, thethree phosphate groups in ATP form a chain that branches from afive-carbon sugar called ribose (RIE bohs). This phosphate “tail” isunstable because the phosphate groups are negatively charged andtherefore repel each other. The phosphate groups store energy like acompressed spring does. This energy is released when the bondsthat hold the phosphate groups together are broken.

Breaking the outer phosphate bond requires an input of energy.Much more energy is released, however, than is consumed by thereaction. As shown in Figure 3, the removal of a phosphate groupfrom ATP produces adenosine diphosphate, or ADP. This reactionreleases energy in a way that enables cells to use the energy. The fol-lowing equation summarizes this reaction:

ATP → ADP � P � energy

Cells use the energy released by this reaction to power metabo-lism. In some chemical reactions, two phosphate groups areremoved from ATP instead of just one. This tends to make the reac-tion irreversible because the pair of phosphate groups that isremoved is not available for the reverse reaction. Rather, the pair isquickly split into two single phosphate groups.

P P P P P

P

Base (adenine)

Phosphate groups

Sugar(ribose)

ATP ADP

Energy

(Adenosine triphosphate) (Adenosine diphosphate)

Identify the primary source of energy that flowsthrough most living systems. 9D

Compare the metabolism of autotrophs withthat of heterotrophs. 9B

Describe how energy is released from ATP.

Critical Thinking Inferring RelationshipsHow can the energy in the food that a fox eats betraced back to the sun? 9D

Critical Thinking Analyzing PatternsExplain how life involves a continuous flow ofenergy. 9D

A grasshopper obtains energyby eating grass. A snake eats the grasshopper, and ahawk then eats the snake. What is the originalsource of energy for the hawk? 12E

A the snake C the grass B the grasshopper D the sun

TAKS Test PrepTAKS Test Prep

5

4

3

2

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Section 1 Review

When the outer phosphate group detaches from ATP, energy is released.

Figure 3 ATP releases energy

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Student Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9D TAKS Obj 4 IPC 8A TEKS Bio 4B, 9B, 9D, 12ETEKS IPC 8A

Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9D, 12B, 12ETEKS Bio 3E, 4A, 4B, 8B, 9A, 9B, 9D,12A, 12B, 12ETEKS IPC 8B

pp. 96–97

Section 2

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. In this section, studentswill learn to describe the majorevents of the three stages of photo-synthesis. These include the captureof energy (stage 1) the conversionof light energy to chemical energy(stage 2), and the formation oforganic compounds using storedchemical energy (stage 3).

On the board or overhead, ask stu-dents to write down the primaryrole that sunlight plays in livingsystems. (Sunlight is the main sourceof energy in living systems.) Thenask students to define photosynthe-sis. (Answers should indicate thatphotosynthesis is the process bywhich organisms use light energy tomake their own food.)

DemonstrationUse a scalpel to make thin crosssections of a potato. Use a projec-tion microscope to show the potatosection, or have students examinethe potato under a compoundmicroscope. Ask them to look forstarch granules, which should appearas large, translucent structures insidethe potato cells. Explain that themuch of the organic compoundsplants make during photosynthesisare stored as starch. VisualTAKS 2 Bio 4B; Bio 4A, 9B

LS

MotivateMotivate

TAKS 3 Bio 9D; Bio 12A

Bellringer

FocusFocus


• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Quick Lab GENERAL

GENERAL

GENERAL

Chapter Resource File• Reading Organizers• Reading Strategies• Basic Skills Worksheet

Reading a ThermometerTemperature Conversions

• Supplemental Reading GuideThe Lives of a Cell

Planner CD-ROMTransparencies

TT BellringerTT Overview of PhotosynthesisTT Absorption Spectra of

Photosynthetic PigmentsTT ChloroplastTT Electron Transport Chains

of PhotosynthesisTT Calvin Cycle

Using the Energy in SunlightWhen you eat a hamburger, you get energy from the sun indirectly.Plants, such as grass, capture the energy in sunlight. The beef in ahamburger comes from a cow that ate grass. The bun, lettuce, andtomato come from plants. With few exceptions, you end up withplants whenever you trace your food back to its origin. Plants, algae,and some bacteria capture about 1 percent of the energy in the sun-light that reaches Earth and convert it to chemical energy throughthe process of photosynthesis.

The Stages of PhotosynthesisPhotosynthesis is the process that provides energy for almost all life.As Figure 4 shows, photosynthesis has three stages:

Stage 1 Energy is captured from sunlight.

Stage 2 Light energy is converted to chemical energy, which is tem-porarily stored in ATP and the energy carrier moleculeNADPH.

Stage 3 The chemical energy stored in ATP and NADPH powers theformation of organic compounds, using carbon dioxide,CO2.

Photosynthesis occurs in the chloroplasts of plant cells and algaeand in the cell membrane of certain prokaryotes. Photosynthesiscan be summarized by the following equation:

3CO2 � 3H2O → C3H6O3 � 3O2

This equation, however, does not showhow photosynthesis occurs. It merely saysthat three carbon dioxide molecules, threewater molecules, and light are needed toform one three-carbon organic compoundand three molecules of oxygen. Plants usethe organic compounds they make duringphotosynthesis to carry out their lifeprocesses. For example, some of these sug-ars are used to form starch, which can bestored in stems or roots. The plant maylater break down the starch to make ATPused to power metabolism. All of the pro-teins, nucleic acids, and other moleculesof the cell are assembled from fragmentsof these sugars.

Photosynthesis Section 2

Objectives● Summarize how energy is

captured from sunlight in thefirst stage of photosynthesis.

● Analyze the function ofelectron transport chains inthe second stage of photo-synthesis.

● Relate the Calvin cycle tocarbon dioxide fixation inthe third stage of photo-synthesis.

● Identify three environmentalfactors that affect the rate ofphotosynthesis.

Key Terms

pigmentchlorophyllcarotenoid thylakoidelectron transportchain

NADPHcarbon dioxidefixation

Calvin cycle carbondioxide

water oxygengas

3-carbonsugar

light

NADP+

Light

NADPH

ADP

H2OO2

CO2

Organiccompounds

Stage 2 Stage 3Stage 1

ATP

The process of photosynthesis occurs in three stages.

Figure 4 Photosynthesis

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TAKS 2

TAKS 3

Teaching TipYellow and orange vegetables arerich in sources of carotenoids. Acarotenoid called beta carotene is animportant dietary source of vitaminA, which is necessary for proper eye-sight, for maintaining the health ofmembranes, and for tooth and bonedevelopment. Have studentsresearch and write a report on theeffectiveness of beta-carotene as anantioxidant. Also have them com-pare the effectiveness of food sourcesof betacarotene with that of othersources, such as dietary supplements.

Verbal

Teaching TipShade-Grown Plants versus Sun-Grown Plants Plants grown in theshade often produce larger leavesthan plants grown in full sunlight.Have students propose a hypothesisto explain this. (The larger leaves ofshade-grown plants gather more sun-light because they have a larger sur-face area available to absorb light.This is advantageous because lesslight reaches the leaves of shade-grown plants.) TAKS 3 13A; Bio 10C

GENERAL

Bio 3B, 9ALS

TeachTeach


did you know?Spectroscopy The study of specific interac-tions of light and matter is spectroscopy. Thespectrophotometer is the instrument used toaccomplish this. Many areas of biology usespectroscopy. The ability of a pigment toabsorb various wavelengths of light can bemeasured using the spectrophotometer. Agraph plotting the pigment’s light absorptionversus wavelength is called an absorptionspectrum. TAKS 5 IPC 5A (grade 10 only), 5B (grade 11 only)

Stage One: Absorption of Light EnergyThe chemical reactions that occur in the first and second stages ofphotosynthesis are sometimes called “light reactions,” or light-dependent reactions. Without the absorption of light, thesereactions could not occur. Light energy is used to make energy-storing compounds. Light is a form of radiation—energy in the formof waves that travel through space. Different types of radiation, suchas light and heat, have different wavelengths (the distance betweentwo consecutive waves). When the sun shines on you, your body isbombarded by many kinds of radiation from the sun. However, youcan see only radiation known as visible light. You see wavelengths ofvisible light as different colors. As shown in Figure 5, sunlight con-tains all the wavelengths of visible light, red through violet.

PigmentsHow does a human eye or a leaf absorb light? These structures con-tain light-absorbing substances called . Pigments absorbonly certain wavelengths and reflect all the others. (KLOR uh fihl), the primary pigment involved in photosynthesis,absorbs mostly blue and red light and reflects green and yellowlight. This reflection of green and yellow light makes many plants,especially their leaves, look green. Plants contain two types ofchlorophyll, chlorophyll a and chlorophyll b. Both types of chloro-phyll play an important role in plant photosynthesis.

The pigments that produce yellow and orange fall leaf colors, aswell as the colors of many fruits, vegetables, and flowers, are called

(kuh RAH tuh noydz). Carotenoids absorb wavelengthsof light different from those absorbed by chlorophyll, so having bothpigments enables plants to absorb more light energy during photo-synthesis. The graph in Figure 6 shows the wavelengths of lightabsorbed by chlorophyll a, chlorophyll b, and carotenoids.

carotenoids

Chlorophyllpigments

Sun

Sunlight

Visible spectrum

Increasing wavelength

400 nm 700 nm

Prism

Wavelength (nm)

Carotenoids

Chlorophyll b

Chlorophyll a

400 500 600 700

Perc

enta

ge o

flig

ht

abso

rbed

Absorption Spectra of Photosynthetic Pigments

Figure 5 Visible spectrum.Sunlight contains a mixture ofall the wavelengths (colors) ofvisible light. When sunlightpasses through a prism, theprism separates the light intodifferent colors.

Figure 6 Light absorptionduring photosynthesis.Chlorophylls absorb mostlyviolet, blue, and red light, whilecarotenoids absorb mostlyblue and green light.

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IPC Benchmark Fact

Since visible light comprises just one small part of the spectrum of electromagnetic waves, this is anopportune time to go over the full range of the elec-tromagnetic spectrum. Point out that other types ofelectromagnetic waves, which require no medium inorder to travel, include gamma rays, X rays, ultraviolet(UV) rays, infrared waves, microwaves, and radiowaves. You might also ask the students to identifywhich waves have a high frequency and are thereforehigh energy.TAKS 5 IPC 5A (grade 10 only), 5B (grade 11 only)

Student Edition TAKS Obj 2 Bio 4B TAKS Obj 4 IPC 8A TAKS Obj 4 IPC 9B TEKS Bio 4BTEKS IPC 8A, 9B

Teacher Edition TAKS Obj 2 Bio 4BTAKS Obj 3 Bio 13ATAKS Obj 5 IPC 5A, 5BTEKS Bio 3B, 4A, 4B, 9A, 10C, 13A, 13BTEKS IPC 5A, 5B

pp. 98–99

Phytoplankton Some of the most numerousorganisms on the planet are phytoplankton.These tiny, floating organisms form the foun-dation of ecosystems in lakes and oceans.Combined, they may be responsible for 40% of photosynthesis on Earth.

Demonstration Use small chocolate mints (about 5 cm diameter) with a white center.Make stacks of four or five mints.On one or two of the stacks, cutthe top mint in half to expose thecenter before putting it on thestack. Point out that each stack ofmints represents a column of thy-lakoids. To make the model morerealistic, connect one stack toanother using strips of paper torepresent the membranous connec-tions between thylakoids. Ask stu-dents why it is more advantageousfor the thylakoids to be in a stackthan in a single unit. (Stacksincrease the surface area available for light absorption by pigment molecules.) Visual

Using the Figure Point out the parts of Figure 7 thatbreak down the structure of achloroplast. Note that a leaf is alsoshown; leaves are the primary sitesof photosynthesis in plants becauseleaf cells contain many chloro-plasts. Leaves are generally thin,allowing sunlight to penetrate intothe cells. Openings in the leaf sur-face allow carbon dioxide to enterand oxygen and water vapor toleave. Visual TAKS 2 Bio 4B; Bio 4A, 13BLS

Bio 4A, 10C, 13BLS


MISCONCEPTION ALERT

Why Plants Look Green Many peoplethink that plants are green because plantsuse green light during photosynthesis. Infact, plants do NOT use green light, andinstead use mainly red and blue light. Tellstudents that plants look green because theycontain chlorophyll, which reflects greenand yellow light while absorbing blue andred light.

Production of OxygenAs shown in Figure 7, pigments involved in plant photosynthesis arelocated in the chloroplasts of leaf cells. Clusters of pigments areembedded in the membranes of disk-shaped structures called

(THIE luh koydz). When light strikes a thylakoid in achloroplast, energy is transferred to electrons in chlorophyll. Thisenergy transfer causes the electrons to jump to a higher energy level.Electrons with extra energy are said to be “excited.” This is howplants first capture energy from sunlight.

Excited electrons jump from chlorophyll molecules to othernearby molecules in the thylakoid membrane, where the electronsare used to power the second stage of photosynthesis. The excitedelectrons that leave chlorophyll molecules must be replaced byother electrons. Plants get these replacement electrons from watermolecules, H2O. Water molecules are split by an enzyme inside thethylakoid. When water molecules are split, chlorophyll moleculestake the electrons from the hydrogen atoms, H, leaving hydrogenions, H+. The remaining oxygen atoms, O, from the disassembledwater molecules combine to form oxygen gas, O2.

thylakoids

www.scilinks.orgTopic: Light AbsorptionKeyword: HX4116

Thylakoidspace

Thylakoid

Thylakoidmembrane

Innermembrane

Cluster ofpigments

Water-splittingenzyme

Thylakoidspace

Outside ofthylakoid

Outermembrane

Chloroplast

Plant cell

Leaf

e–

4H+

2H2O O2

Thylakoidmembrane

Pigment molecules are embedded in thylakoid membranes, as are othermolecules that participate in photosynthesis.

Figure 7 Chloroplast

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When an electron in an atom is boosted to ahigher energy level, it gains energy. When anelectron drops back to a lower energy level, itemits energy. These emissions often take theform of electromagnetic waves that are alwaysspecific to the magnitude of the drop inenergy. Emissions may be above or below thevisible range of the electromagnetic spectrum.TAKS 4 IPC 8A; IPC 8B

CHEMISTRYCHEMISTRYCONNECTIONCONNECTION

CareerCareerHorticulturist Arrange for a guided tour of anearby botanical garden with a horticulturist.Before the trip, explain that horticulturistsgrow plants and trees for use as ornamentals orfood. Have students prepare questions thatthey would like to ask the horticulturist aboutplants, as well as details of their career.At the site, ask the horticulturist to point outplants that have different light, temperature,and mineral requirements before answeringstudent questions. Visual TAKS 3 Bio 13A; Bio 10C, 13B

LS

Using the FigureFigure 8 follows the path of electrontransport during the light-dependentreactions of photosynthesis. Guidestudents through the electron trans-port chains of photosynthesis by asking the following questions: What is the source of the excitedelectrons? (chlorophyll molecules)What is the source of some of thereplacement electrons? (split watermolecules) What type of transportoccurs when hydrogen ions arepumped into the thylakoid? (activetransport) What type of transportoccurs when hydrogen ions move out of the thylakoid? (passive trans-port) What kind of membraneprotein is involved? (carrier protein)Have students record the questionsand answers in their notebooks.

Visual TAKS 2 Bio 4B, TAKS 4 IPC8A, 9B; Bio 4A, 9A, 9B, 13B; IPC 8B

Teaching TipStages of Photosynthesis Helpstudents remember the three stagesof photosynthesis by having themmake flash cards with a structure orprocess on one side and a descriptionof its role on the other side. Topicsshould include pigment molecules,thylakoids, electron transport chains,ATP, and NADPH. Visual TAKS 2Bio 4B; Bio 4A, 9A, 10C

LS

GENERAL

LS

GENERAL


Stage Two: Conversion of Light Energy Excited electrons that leave chlorophyll molecules are used toproduce new molecules, including ATP, that temporarily storechemical energy. First an excited electron jumps to a nearby mol-ecule in the thylakoid membrane. Then the electron is passedthrough a series of molecules along the thylakoid membrane like aball being passed down a line of people. The series of moleculesthrough which excited electrons are passed along a thylakoid mem-brane are called . Trace the path taken byexcited electrons in the electron transport chains shown in Figure 8.

Electron Transport ChainsHow are electron transport chains used to make molecules thattemporarily store energy in the cell? The first electron transportchain shown in Figure 8 lies between the two large green clusters ofpigment molecules. This type of electron transport chain contains aprotein (the large purple molecule) that acts as a membrane pump.Excited electrons lose some of their energy as they each pass throughthis protein. The energy lost by the electrons is used to pump hydro-gen ions, H�, into the thylakoid. Recall that hydrogen ions are alsoproduced when water molecules are split inside the thylakoid.

As the process continues, hydrogen ions become more concen-trated inside the thylakoid than outside, producing a concentrationgradient across the thylakoid membrane. As a result, hydrogen ionshave a tendency to diffuse back out of the thylakoid down their

electron transport chains

H+

H+ H+

H+

H+

H+

H+

H+H+

H+ H+

H+

H+ H+

H+H+

H+

H+

P

e-

e-

e-

Light

Pigments

Thylakoid

ATP-producingcarrier protein

2 H2O

O2

4 H+

Path of electrons

Hydrogen ions, H+

NADP+ +

Light

Water-splittingenzyme

NADPH

ADP + ATP

Electron transport chains (represented by the red lines) convert light energy to chemical energy.

Figure 8 Electron transport chains of photosynthesis

Interpreting GraphicsLook closely at Figure 8.Electrons are represented by the symbol e–. The redarrows show the path ofexcited electrons. Hydrogenions are represented by thesymbol H+. The blue arrowsshow the path of hydrogenions that cross the thylakoidmembrane.

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Teacher Edition TAKS Obj 2 Bio 4BTAKS Obj 3 Bio 13ATAKS Obj 4 IPC 8A, 9BTEKS Bio 4A, 4B, 9A, 9B, 10C, 13A, 13BTEKS IPC 8A, 8B

pp. 100–101

Teaching TipGraphic Organizer Have studentsmake a Graphic Organizer similar to the one at the bottom of thispage to illustrate the substances usedand produced during each stage ofphotosynthesis. VisualLS


Identifying aProduct ofPhotosynthesisSkills AcquiredInferring, analyzing,evaluating

Teacher’s NotesThe Elodea should be placed inthe test tube cut-side up; the cutshould be fresh. Be carefulworking with glass.

Answers to Analysis 1. Answers will vary. For exam-

ple, oxygen is produced aswater molecules are split in theelectron transport chains ofElodea.

2. A control could be a cutting ofElodea under all of the sameconditions except exposure tolight.

3. If the probe detects an increasein the oxygen content of thewater, then the hypothesis thatphotosynthetic organisms giveoff oxygen is supported.

Graphic Organizer

Stages of PhotosynthesisUsed Produced

Stage 1 Light, water Oxygen, hydrogen ionsStage 2 Electrons, hydrogen ions ATP, NADPHStage 3 ATP, NADPH, Organic compounds

carbon dioxide

Use this graphic organizer withTeaching Tip on this page.

concentration gradient through specialized carrier proteins (illus-trated on the lower surface of the thylakoid). These carrier proteinsare unusual because they function both as an ion channel and as anenzyme. As hydrogen ions pass through the channel portion of theprotein, the protein catalyzes a reaction in which a phosphate groupis added to a molecule of ADP, making ATP. Thus, the movement ofhydrogen ions across the thylakoid membrane through these pro-teins provides the energy needed to make ATP, which is used topower the third stage of photosynthesis.

While one electron transport chain provides energy used to makeATP, a second electron transport chain provides energy used tomake NADPH. is an electron carrier that provides the high-energy electrons needed to make carbon-hydrogen bonds in the thirdstage of photosynthesis. The second electron transport chain shownin Figure 8 lies to the right of the second green pigment molecule. Inthis second chain, excited electrons combine with hydrogen ions aswell as an electron acceptor called NADP+, forming NADPH.

The light-dependent reactions of photosynthesis can be summa-rized as follows. Pigment molecules in the thylakoids of chloroplastsabsorb light energy. Electrons in the pigments are excited by light andmove through electron transport chains in thylakoid membranes.These electrons are replaced by electrons from water molecules, whichare split by an enzyme. Oxygen atoms from water molecules combineto form oxygen gas. Hydrogen ions accumulate inside thylakoids,setting up a concentration gradient that provides the energy to makeATP and NADPH.

NADPH

Identifying a Productof Photosynthesis You can use the following procedure to identify the gas given off by a photosynthetic organism.

Materials

MBL or CBL system with appropriate software, test tube orsmall glass jar, sprig of Elodea, distilled water, cool lightsource, dissolved oxygen (DO) probe

Procedure

1. Set up an MBL/CBL systemto collect and graph datafrom a dissolved oxygenprobe at 30-second intervalsfor 60 data points. Calibratethe DO probe.

2. Place a sprig of Elodeain a test tube or glass

jar, and fill the test tube or jarwith distilled water.

3. Place the test tube or glassjar under a cool light source,and lower a DO probe intothe water. Collect data for 30minutes.

4. When data collection iscomplete, view the graph ofyour data. If possible, printthe graph. Otherwise, sketchthe graph on paper.

Analysis

1. Infer the cause of anychange you observed.

2. Propose a control for thisexperiment.

3. Critical ThinkingEvaluating HypothesesExplain how your data supportor do not support the hypoth-esis that photosyntheticorganisms give off oxygen.

4B

101

TAKS 2Bio 4B

TAKS 2

Using the FigureHave students count thetotal number of carbonatoms present at each

step in the summary of the Calvincycle, in Figure 9. Ask students thefollowing questions: How are ATPand NADPH important to theCalvin cycle? (They supply energyused to form new compounds.) Howmany carbon dioxide molecules areneeded? (3) How many 3-carbonsugars are made? (6) How many ofthese sugars are actually used tomake organic compounds that theplant uses for energy? (1) Emphasizethat most of the 3-carbon sugars are“recycled” and used to make thestarting 5-carbon compound thatbegins the cycle again. Visual

Activity Identifying Variables Have stu-dents list three factors that wouldincrease the rate of photosynthesis.Have them identify what stage ofphotosynthesis each factor wouldaffect. (Examples might includeincreasing light intensity, whichwould affect Stage 1; providing morewater, which would affect Stage 2;and increasing the carbon dioxideconcentration, which would affectStage 3.) TAKS 2 Bio 4B; Bio 4A, 9B, 9C

LS

GENERAL


Trends in Plant Physiology Increasing Carbon Dioxide Researchersaround the world are studying plant responsesto increasing atmospheric carbon dioxide. Ingeneral, more carbon dioxide means that morebiomass, or plant tissue, is made during photo-synthesis. This may help to counter the effectsof rising carbon dioxide levels caused by burn-ing fossil fuels. Other effects appear to be areduction of nutrients in plant tissues, whichmay impact the heterotrophs that feed on theplants.


BIOgraphic

C

C C C C C

C C C

BIOgraphic

Six 3-carbon

compounds

Three5-carbon

compounds

Threecarbon dioxide

molecules

Six 3-carbonsugars

3 CO2

P

P

P

3 ATP

3 ADP

6 ATP

6 ADP

6 NADPH

6 NADP+

Organiccompounds

C C C P6

C C C P6

One3-carbon

sugar

1

The Calvin cycle is a common method of carbon dioxide fixation.

Calvin Cycle

The other five three-carbon sugars regenerate the five-carbon compound that began the cycle.

4

A CO2 molecule is added to a five-carbon compound.

1

The three resulting six-carbon compounds split, forming a total of six three-carbon compounds.

2

One three-carbon sugar is used to make organic compounds.

3

Figure 9

Stage Three: Storage of EnergyIn the first and second stages of photosynthesis, light energy is usedto make ATP and NADPH, which temporarily store chemical energy.These stages are therefore considered light-dependent. In the third(final) stage of photosynthesis, however, carbon atoms from carbondioxide in the atmosphere are used to make organic compounds inwhich chemical energy is stored. The transfer of carbon dioxide toorganic compounds is called . The reactionsthat “fix” carbon dioxide are sometimes called “dark reactions,” orlight-independent reactions. Among photosynthetic organisms,there are several ways in which carbon dioxide is fixed.

Calvin CycleThe most common method of carbon dioxide fixation is the Calvincycle. The is a series of enzyme-assisted chemicalreactions that produces a three-carbon sugar. The Calvin cycle issummarized in Figure 9.

Step In carbon dioxide fixation, each molecule of carbon dioxide,CO2, is added to a five-carbon compound by an enzyme.

Calvin cycle

carbon dioxide fixation

102


Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9DTAKS Obj 5 IPC 6DTEKS Bio 4A, 4B, 9A, 9B, 9C, 9D, 10CTEKS IPC 6D

pp. 102–103IPC Benchmark Mini Lesson

Biology/IPC Skills TAKS 5 IPC 6D Investigate theenvironmental impact of using various energysources, such as rechargeable batteries and solarcells. Activity Have students use the Internet or thelibrary to research current technology for alternativeenergy storage. Ask students to choose one topic andreport on the environmental and economic impact ofthe technology.

TAKS 2 Bio 4B; TAKS 3 Bio 9D; Bio 4A, 9A, 9B


1. Certain pigments within the cells absorbspecific wavelengths of light energy.

2. Water molecules are split to provide new elec-trons for the electron transport chain andhydrogen ions. The excited electrons provideenergy used to pump even more hydrogen ionsinto the thylakoid. The hydrogen ions then dif-fuse out of the thylakoid in a process thatmakes ATP.

3. Carbon dioxide is used in the Calvin cycle toproduce a 3-carbon sugar that will be used toproduce glucose and other organic compounds.Most of the 3-carbon sugars are recycled.TAKS 2 Bio 4B

TAKS 2 Bio 4B4. Answers will vary, but may be similar to the

table on the right. 5. Factors include light intensity, water

availability, carbon dioxide concentration, and temperature.

6. A. Incorrect. The loss of a phos-phate from ATP forms ADP and releasesenergy. B. Incorrect. Energy is not stored inCO2. C. Correct. Energy stored in 3-carbonsugars is used to make other organic com-pounds. D. Incorrect. Water is not directlyinvolved in the Calvin cycle. TAKS 2 Bio 4B

TAKS 3 Bio 9D

TAKS 2 Bio 4B

ReteachingForm six cooperative groups of stu-dents. Assign one of the followingfactors to each group: water,chlorophyll, light, carbon dioxide,NADPH, and ATP. Have eachgroup decide on the role their fac-tor plays in photosynthesis. After adesignated time, select a person ineach group to read the decision ofthe group to the rest of the class.

Interpersonal

Quiz1. True or false: Chloroplasts are

found within the thylakoid mem-branes. (False. Thylakoids are thesmall disk shaped structures foundwithin the chloroplasts.)

2. True or false: Carbon dioxidefixation takes place during theCalvin cycle. (True. The Calvincycle is the most common methodof carbon dioxide fixation.)

3. The electron transport chainconverts light energy to chemicalenergy during the ________ stageof photosynthesis. (second)

AlternativeAssessmentHave students describe the eventsof the Calvin cycle from the per-spective of one of the carbon atomsin a carbon dioxide molecule.Students should include the mainevents of each of the four steps.

GENERAL

Co-op LearningLS

CloseClose


Answer

Most houseplants are small andable to grow in a small amountof soil with relatively low light.

Real Life

Light Excites electronsWater Provides hydrogen ions and

replacement electronsPigments Absorb lightATP and NADPH Store chemical energyCarbon dioxide Used to produce organic

compounds

Step The resulting six-carbon compound splits into two three- carbon compounds. Phosphate groups from ATP andelectrons from NADPH are added to the three-carbon com-pounds, forming three-carbon sugars.

Step One of the resulting three-carbon sugars is used to makeorganic compounds—including starch and sucrose—inwhich energy is stored for later use by the organism.

Step The other three-carbon sugars are used to regenerate theinitial five-carbon compound, thereby completing the cycle.

The Calvin cycle is named for Melvin Calvin, the American bio-chemist who worked out the chemical reactions in the cycle. Thereactions are cyclic—they recycle the five-carbon compound neededto begin the cycle again. A total of three carbon dioxide moleculesmust enter the Calvin cycle to produce each three-carbon sugar thatwill be used to make other organic compounds. These organiccompounds provide the organism with energy for growth andmetabolism. The energy used in the Calvin cycle is supplied by ATPand NADPH made during the second stage of photosynthesis.

Factors that Affect PhotosynthesisPhotosynthesis is directly affected by various environmental factors.The most obvious of these factors is light. In general, the rate ofphotosynthesis increases as light intensity increases until all thepigments are being used. At this saturation point, the rate of photo-synthesis levels off because pigments cannot absorb any more light.The carbon dioxide concentration affects the rate of photosynthesisin a similar manner. Once a certain concentration of carbon dioxideis present, photosynthesis cannot proceed any faster.

Photosynthesis is most efficient within a certain range of tem-peratures. Like all metabolic processes, photosynthesis involvesmany enzyme-assisted chemical reactions. Recall that unfavorabletemperatures may inactivate certain enzymes.

Real LifeSome houseplants thrivein dim light. A plant inside a home mayreceive 100 times lessbright light than it would ifit were grown outdoors. Recognizing Patterns Examine several speciesof houseplants in a store or nursery.What featuresare commonamonghouse-plants?

www.scilinks.orgTopic: Factors Affecting

PhotosynthesisKeyword: HX4079

Section 2 Review

Summarize how photosynthetic organismscapture the energy in sunlight. 4B

Compare the roles of water molecules andhydrogen ions in electron transport chains.

Describe the role of the Calvin cycle in the thirdstage of photosynthesis.

Critical Thinking Organizing InformationMake a table in which you identify the role of eachof the following in photosynthesis: light, water,pigments, ATP, NADPH, and carbon dioxide.

Critical Thinking Inferring RelationshipsWhat combination of environmental factorsaffects the rate of photosynthesis? 9D

During photosynthesis,plants store energy in A ADP. C 3-carbon sugars. B carbon dioxide. D water.


4B

103

Bio 9B, 10C

g4B

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. In this section students willlearn how organic compounds arebroken down into ATP, the energycurrency of all cells. Students willlearn the basic events of glycolysisand cellular respiration, as well asalternate energy pathways that takeplace in the absence of oxygen.TAKS 2 Bio 4B; Bio 4A, 9A, 9B; IPC 8B

Ask students to answer the follow-ing questions in their notebooks:How are the products of photosyn-thesis and respiration related? (Theproducts of photosynthesis are thestarting materials for respiration.)What kinds of organisms undergocellular respiration? (All organisms,including photosynthetic organisms,undergo cellular respiration as long asoxygen is available.)

IdentifyingPreconceptionsAsk students what they know aboutfermentation. Students may speak ofrotting, foul smells, or alcohol pro-duction. Explain that fermentationis a way that cells are able to makeATP when in the absence of oxygen.Fermentation can cause foul odors.It also helps produce cheese, yogurt,bread, and wine. Tell them that ifthey ever exercised to the point ofsoreness and cramping, they mayhave forced their muscle cells toundergo fermentation. TAKS 2 Bio 4B; Bio 9A, 9B

MotivateMotivate

TAKS 2 Bio 4B; Bio 9B

Bellringer

FocusFocus

Section 3


• Lesson Plan• Directed Reading• Active Reading GENERAL

GENERAL


• Reading Organizers• Reading Strategies • Supplemental Reading Guide

The Lives of a Cell

Planner CD-ROM

Transparencies

TT BellringerTT Cellular RespirationTT GlycolysisTT Krebs CycleTT Electron Transport Chain of

Aerobic Respiration

Section 3 Cellular Respiration

Cellular EnergyMost of the foods we eat contain usable energy. Much of the energyin a hamburger, for example, is stored in proteins, carbohydrates,and fats. But before you can use that energy, it is transferred to ATP.Like in most organisms, your cells transfer the energy in organiccompounds, especially glucose, to ATP through a process calledcellular respiration. Oxygen in the air you breathe makes the pro-duction of ATP more efficient, although some ATP is made withoutoxygen. Metabolic processes that require oxygen are called (ehr OH bihk). Metabolic processes that do not require oxygen arecalled (AN ehr oh bihk), meaning “without air.”

The Stages of Cellular RespirationCellular respiration is the process cells use to harvest the energy inorganic compounds, particularly glucose. The breakdown of glucoseduring cellular respiration can be summarized by the followingequation:

C6H12O6 � 6O2 → 6CO2 � 6H2O � energy

As Figure 10 shows, cellular respiration occurs in two stages:

Stage 1 Glucose is converted to pyruvate (PIE roo vayt), producinga small amount of ATP and NADH.

Stage 2 When oxygen is present, pyruvate and NADH are used to make a large amount of ATP. This process is called aero-

bic respiration. Aerobic respirationoccurs in the mitochondria of eukary-otic cells and in the cell membrane ofprokaryotic cells. When oxygen is notpresent, pyruvate is converted to eitherlactate (LAK tayt) or ethanol (ethyl alco-hol) and carbon dioxide.

The equation above does not showhow cellular respiration occurs. It simplyshows that the complete enzyme-assistedbreakdown of a glucose molecule usessix oxygen molecules and forms sixcarbon dioxide molecules, six watermolecules, and ATP. Aerobic respirationproduces most of the ATP made by cells.Intermediate products of aerobic respi-ration form the organic compounds thathelp build and maintain cells.

anaerobic

aerobic

Objectives● Summarize how glucose is

broken down in the firststage of cellular respiration.

● Describe how ATP is madein the second stage of cellu-lar respiration.

● Identify the role of fermen-tation in the second stage ofcellular respiration.

● Evaluate the importance of oxygen in aerobic respiration.

Key Terms

aerobicanaerobicglycolysis NADHKrebs cycleFADH2fermentation

enzymes

oxygengas

glucose carbondioxide

water ATP

Glucose

Stage 1

Stage 2

Aerobic(with O2)

Anaerobic(without O2)

Pyruvate

Ethanoland CO2, or

lactate

ATP

ATP

ADP

Mitochondrion

NAD+

NADH

1. First, glucose is broken down to pyruvate.

2. Then, either aerobic respiration or anaerobic processes occur.

Cellular respiration occurs in two stages.

Figure 10Cellular respiration

4B

4B

4B

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Student Edition TAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9D TAKS Obj 4 IPC 8A TAKS Obj 4 IPC 9B TEKS Bio 4B, 9DTEKS IPC 8A, 9B

Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 4 IPC 8ATEKS Bio 4A, 4B, 9A, 9BTEKS IPC 8A, 8B

pp. 104–105

TAKS 2

TAKS 2

TAKS 2

Teaching Tip Metabolic Pathways Review theterm metabolism with students.(Metabolism describes the sum of allchemical reactions within an organ-ism.) Tell students that glycolysis isan example of a metabolic path-way. In glycolysis, the energy storedin glucose is gradually released in aseries of enzyme–assisted chemicalreactions. TAKS 2 Bio 4B; Bio 9A, 9B;IPC 8B

Using the FigureHave students examine Figure 11,then ask them to identify the start-ing material in glycolysis. (glucose)Work with students to summarizethe events that take place in eachstep. Explain that as glucose is bro-ken down during glycolysis, someof the energy contained in glucoseis transferred to the products ofglycolysis. Ask students to identifythese products. (pyruvate, ATP, andNADH) Explain that pyruvate isthe ion of the organic moleculepyruvic acid. Visual

Anticipation Guide Write the fol-lowing statements on the board:

1. Organisms do not need oxygento get energy from organic mole-cules.

2. It is unlikely that humans willever run 1,600 m (about 1 mi.)in less than 2 minutes.

Ask students to think about eachstatement and decide whether theyagree or disagree. Students shouldpoint to specific passages in thetext that support their reasoning.After discussion, ask them if theiropinions have changed. LogicalLS

GENERALSKILLBUILDER

READINGREADING

Bio 9A, 9B; IPC 8BLS

GENERAL

TeachTeach


did you know?Life Without Oxygen Early life probably usedglycolysis to make ATP long before oxygenwas present in Earth’s atmosphere. Accordingto fossil records, prokaryotes were present onEarth 3.5 billion years ago, but oxygen was notabundant in the atmosphere until around 2.5billion years ago. Because glycolysis is ananaerobic metabolic pathway that occurs in allcells, glycolysis most likely occurred in earlycells. Bio 4B, 9A

Stage One: Breakdown of GlucoseThe primary fuel for cellular respiration is glucose, which is formedwhen carbohydrates such as starch and sucrose are broken down. Iftoo few carbohydrates are available to meet an organism’s glucoseneeds, other molecules, such as fats, can be broken down to makeATP. In fact, one gram of fat contains more energy than two grams ofcarbohydrates. Proteins and nucleic acids can also be used to makeATP, but they are usually used for building important cell parts.

GlycolysisIn the first stage of cellular respiration, glucose is bro-ken down in the cytoplasm during a process called

(glie KAHL uh sihs). Glycolysis is anenzyme-assisted anaerobic process that breaks downone six-carbon molecule of glucose to two three-carbon pyruvate ions. Recall that a molecule that haslost or gained one or more electrons is called an ion.Pyruvate is the ion of a three-carbon organic acidcalled pyruvic acid. The pyruvate produced during gly-colysis still contains some of the energy that wasstored in the glucose molecule.

As glucose is broken down, some of its hydrogenatoms are transferred to an electron acceptor calledNAD�. This forms an electron carrier called .For cellular respiration to continue, the electrons car-ried by NADH are eventually donated to other organiccompounds. This recycles NAD�, making it availableto accept more electrons. Glycolysis is summarized inFigure 11.

Step In a series of three reactions, phosphategroups from two ATP molecules are trans-ferred to a glucose molecule.

Step In two reactions, the resulting six-carbon com-pound is broken down to two three-carboncompounds, each with a phosphate group.

Step Two NADH molecules are produced, and onemore phosphate group is transferred to eachthree-carbon compound.

Step In a series of four reactions, each three-carboncompound is converted to a three-carbonpyruvate, producing four ATP molecules inthe process.

Glycolysis uses two ATP molecules but produces fourATP molecules, yielding a net gain of two ATP mol-ecules. Glycolysis is followed by another set of reactionsthat use the energy temporarily stored in NADH tomake more ATP.

NADH

glycolysis

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC




BIOgraphicBIOO

Glucose

6-carboncompound

Two 3-carbonpyruvates

Two 3-carboncompounds

Two 3-carboncompounds

2 ADP

2 NAD+

2 NADH + 2HNADH +

2

4 ADP

1

2

3

4

Glycolysis

Figure 11

105

Teaching Tip Coenzymes A coenzyme is anorganic chemical that is necessaryfor the action of many enzymes.Ask students why it is important forglucose to be partially broken downto pyruvate. (Unlike glucose, pyru-vate is small enough to diffuse acrossthe mitochondrial membranes.) Tellstudents that when pyruvate entersa mitochondrion and is brokendown to a 2-carbon acetyl group,coenzyme A attaches to the acetylgroup, forming acetyl-CoA.Coenzyme A enables the acetylgroup to enter the Krebs cycle. TAKS 2 Bio 4B; Bio 4A, 9A, 9B, 9C; IPC 8B

Using the FigureGuide students through the steps ofFigure 12. Have students count thenumber of carbon atoms present ateach step during the Krebs cycle.Ask them where the Krebs cycleoccurs. (in mitochondria) Remindstudents that for every molecule ofglucose that is broken down, twopyruvate ions are produced. Thusthe Krebs cycle occurs for eachpyruvate. Also tell them that a spe-cific enzyme is involved in eachstep. Emphasize the role of theKrebs cycle as a precursor of theelectron transport chain. VisualTAKS 2 Bio 4B; Bio 9A, 9B, 9C; IPC 8B

LS



C C C C C C

C C C C C

C C C CC C C C

C C C C

C

C

BIOgraphic

The Krebs cycle produces electron carriers that temporarily store chemical energy.

Krebs Cycle

C CAcetyl-CoA

6-carboncompound

5-carboncompound

4-carboncompound

4-carboncompound

4-carboncompound

CoA

NAD+

NADH + H+

NAD+

NAD+ NADH + H+

NADH + H+

ADP +

ATP

FADFADH2

CO2

CO2

1. Acetyl-CoA combines with a four-carbon compound, forming a six-carbon compound.

2. CO2 is released from the six-carbon compound, leaving a five-carbon compound.

3. CO2 is released from the five-carbon compound, leaving a four-carbon compound.

4. The four-carbon compound is converted to a new four-carbon compound.

5. The new four-carbon compound is converted to the four-carbon compound that began the cycle.

P

1 2

5

3

4

Stage Two: Production of ATP When oxygen is present, pyruvate produced during glycolysis entersa mitochondrion and is converted to a two-carbon compound. Thisreaction produces one carbon dioxide molecule, one NADH mole-cule, and one two-carbon acetyl (uh SEET uhl) group. The acetylgroup is attached to a molecule called coenzyme A (CoA), forming acompound called acetyl-CoA (uh SEET uhl-koh ay).

Krebs CycleAcetyl-CoA enters a series of enzyme-assisted reactions called the

, summarized in Figure 12. The cycle is named for thebiochemist Hans Krebs, who first described the cycle in 1937.

Step Acetyl-CoA combines with a four-carbon compound, form-ing a six-carbon compound and releasing coenzyme A.

Step Carbon dioxide, CO2, is released from the six-carbon com-pound, forming a five-carbon compound. Electrons aretransferred to NAD+, making a molecule of NADH.

Krebs cycle

Figure 12

106

Student Edition TAKS Obj 2 Bio 4B TAKS Obj 4 Bio IPC 8A TAKS Obj 4 Bio IPC 9B TEKS Bio 4BTEKS IPC 8A, 9B

Teacher Edition TAKS Obj 2 Bio 4B TAKS Obj 4 IPC 8A TEKS Bio/IPC 3CTEKS Bio 3F, 4A, 4B, 9A, 9B, 9CTEKS IPC 8B

pp. 106–107

IPC Benchmark Fact

Remind students that the end products of photosyn-thesis and cellular respiration are produced as theresult of complex chemical changes that the reactantsundergo. In order to review and stress the chemicalchanges that occur in these essential metabolicprocesses, have students identify the reactants andproducts in the overall chemical reactions of photo-synthesis and cellular respiration. Ask advancedstudents to do the same exercise with the Calvincycle, glycolysis, and the Krebs cycle. TAKS 4 IPC 8A

ATP Molecules The human body uses about1 million molecules of ATP per cell per second. There are more than 100 trillion cells in thehuman body. That's about 1 � 1020, or100,000,000,000,000,000,000 ATP moleculesused in your body each second!

Teaching TipElectron Transport Ask studentshow the electron transport chainsof photosynthesis and cellular res-piration are similar. (In bothprocesses, electrons are passed alongan electron transport chain and arepicked up by an electron acceptor.The energy of these electrons is usedto produce a hydrogen ion concentra-tion gradient, which provides theenergy needed to make ATP.) TAKS 2Bio 4B; Bio 9A, 9B; IPC 8B

Using the FigureIn Figure 13 have students followthe path of electrons, shown by thered arrows, through the electrontransport chain. Point out that theenergy of these electrons is used topump hydrogen ions out of theinner compartment. Ask studentsto identify this type of transport.(active transport) These ions thendiffuse back into the inner com-partment through the specializedcarrier protein (ATP synthase), pro-viding enough energy to make ATP.Ask students to identify this type oftransport. (passive transport) Askstudents why the folds of the mito-chondria are important. (Theyincrease the surface area of the mem-branes, which allows more ATP to bemade.) Ask students to identify therole of oxygen in the electron trans-port chain. (Oxygen is the final elec-tron acceptor, and water is producedwhen the spent electrons, hydrogenions, and oxygen combine.) VisualTAKS 2 Bio 4B; Bio 9A, 9B; IPC 8B

LS

GENERAL


CulturalAwarenessCulturalAwareness

Hans Adolph Krebs In 1937 Hans AdolphKrebs discovered the details of the Krebscycle. In 1953 Krebs was awarded theNobel Prize in physiology or medicine forhis discovery. Have students research andprepare a report on the life of Krebs, whohad to interrupt his work and leave NaziGermany prior to World War II because hewas Jewish. Bio/IPC 3C; Bio 3F

GENERAL

Step Carbon dioxide is released from the five-carbon compound,resulting in a four-carbon compound. A molecule of ATP ismade, and a molecule of NADH is also produced.

Step The existing four-carbon compound is converted to a newfour-carbon compound. Electrons are transferred to anelectron acceptor called FAD, making a molecule of FADH2.

is another type of electron carrier.

Step The new four-carbon compound is then converted to thefour-carbon compound that began the cycle. Another mol-ecule of NADH is produced.

After the Krebs cycle, NADH and FADH2 now contain much of theenergy that was previously stored in glucose and pyruvate. When theKrebs cycle is completed, the four-carbon compound that began thecycle has been recycled, and acetyl-CoA can enter the cycle again.

Electron Transport ChainIn aerobic respiration, electrons donated by NADH and FADH2 passthrough an electron transport chain, as shown in Figure 13. Ineukaryotic cells, the electron transport chain is located in the innermembranes of mitochondria. The energy of these electrons is used topump hydrogen ions out of the inner mitochondrial compartment.Hydrogen ions accumulate in the outer compartment, producing aconcentration gradient across the inner membrane. Hydrogen ionsdiffuse back into the inner compartment through a carrier proteinthat adds a phosphate group to ADP, making ATP. At the end of theelectron transport chain, hydrogen ions and spent electrons combinewith oxygen molecules, O2, forming water molecules, H2O.

FADH2

www.scilinks.orgTopic: Aerobic RespirationKeyword: HX4004

In the inner membranes of mitochondria, electron transport chains (represented by the red lines) make ATP.

Figure 13 Electron transport chain of aerobic respiration

H+

H+

H+

H+

H+

H+H+

H+H+

H+

H+

H+

P

e-

e-

Inner compartment

Outer compartment

ATP-producingcarrier protein

Innermitochondrial

membrane+

NAD+

2H2O4H+ + O2

ADP +

NADH

ATP

1. The electron transport chain pumps hydrogen ions, H+, out of the inner compartment.

2. At the end of the chain, electrons and hydrogen ions combine with oxygen, forming water.

3. ATP is produced as hydrogen ions diffuse into the inner compartment through a channel protein.

107


CareerCareer

Teaching TipInvite one of the physical educationteachers or coaches from yourschool to discuss the physiologicaleffects of exercise on the body. Becertain that the speaker discussesoxygen debt, muscle fatigue, therole of myoglobin in muscles, andthe role of lactate in muscle soreness.

Intrapersonal TAKS 2 Bio 4B; Bio 10A, 10B (grade 11 only); Bio 9B, 11C

Group Activity Fermentation Have studentswork in groups of four. Each groupshould brainstorm a list of foodsand beverages that make use of fer-mentation. Students may wish touse the Web to expand their list.For presentation, students shouldprepare a poster, using drawings orpictures of fermentation productscut out from magazines. (Answerswill vary, but could include variousbreads, pizza, various cheeses, beer,wine, soy sauce, doughnuts, etc.)

Interpersonal

TAKS 2 Bio 4B; TAKS 3 Bio 4D; Bio 9A

Co-op LearningLS

LS

did you know?Cyanide shuts down the electron transportchain. Cyanide is a fast-acting poison thatblocks the action of the electron transportchain. It exists as hydrogen cyanide gas orcyanide salts used in gold and other metalextractions, electroplating, and metal cleaning.Cyanide enters the body by absorption throughthe lungs, skin, or gastrointestinal tract. It ishighly toxic, and symptoms appear soon afterexposure. Ingesting as little as 3 g of cyanidecan be fatal. TAKS 2 Bio 4B; Bio 11B

Fitness Trainer Many people use health clubsto exercise or work out. These clubs employfitness trainers to direct exercise programs forgroups or custom-tailor programs for individu-als. Have students prepare a report describingthe education requirements and responsibilitiesof a fitness trainer. Bio 3D, 11C

C C C C C C

C C C

C C C C C C

C C C C

C

C

C C C CC C

C

Glucose

In lactic acid fermentation, pyruvate is converted to lactate. In alcoholic fermentation, pyruvate is broken down to ethanol, releasing carbon dioxide, CO2.

Lactic acid fermentation Alcoholic fermentation

PyruvateGlycolysis Glycolysis

NAD+ NADH + H+ NAD+ NADH + H+

Glucose Pyruvate

CO2

Lactate Ethanol 2-carboncompound

Fermentation in the Absence of OxygenWhat happens when there is not enough oxygen for aerobic respi-ration to occur? The electron transport chain does not functionbecause oxygen is not available to serve as the final electron accep-tor. Electrons are not transferred from NADH, and NAD� thereforecannot be recycled. When oxygen is not present, NAD� is recycled inanother way. Under anaerobic conditions, electrons carried byNADH are transferred to pyruvate produced during glycolysis. Thisprocess recycles NAD� needed to continue making ATP through gly-colysis. The recycling of NAD� using an organic hydrogen acceptoris called . Prokaryotes carry out more than a dozenkinds of fermentation, all using some form of organic hydrogenacceptor to recycle NAD�. Two important types of fermentation arelactic acid fermentation and alcoholic fermentation. Lactic acid fer-mentation by some prokaryotes and fungi is used in the productionof foods such as yogurt and some cheeses, as shown in Figure 14.

Lactic Acid FermentationIn some organisms, a three-carbon pyruvate is converted to a three-carbon lactate through lactic acid fermentation, as shown in Figure 15. Lactate is the ion of an organic acid called lactic acid. Forexample, during vigorous exercise pyruvate in muscles is convertedto lactate when muscle cells must operate without enough oxygen.Fermentation enables glycolysis to continue producing ATP in mus-cles as long as the glucose supply lasts. Blood removes excess lactatefrom muscles. Lactate can build up in muscle cells if it is notremoved quickly enough, sometimes causing muscle soreness.

fermentation

Figure 14 Fermentation.In cheese making, fungi orprokaryotes added to milkcarry out lactic acid fermenta-tion on some of the sugar inthe milk.

When oxygen is not present, cells recycle NAD+ through fermentation.

Figure 15 Two types of fermentation

108

Student Edition TAKS Obj 2 Bio 4B TAKS Obj 4 IPC 8A TAKS Obj 4 IPC 9B TAKS Obj 4 IPC 7D TEKS Bio 4BTEKS IPC 7D, 8A, 9B

Teacher Edition TAKS Obj 2 Bio 4B, 10A, 10B TAKS Obj 3 Bio 4DTAKS Obj 4 IPC 9BTEKS Bio 3D, 4B, 4D, 9A, 9B, 10A,10B, 11B, 11CTEKS IPC 9B

pp. 108–109

Demonstration Thoroughly mix half a packet ofyeast with about 400 mL of warmwater. Pour the mixture into anErlenmeyer flask or a beaker. Add afew drops of bromothymol blueindicator and set the flask aside.Ask students what the bubbles indi-cate. (Carbon dioxide is beingreleased by the yeast.) By the end of the class period, the blue yeastmixture should turn yellow. Askstudents why this happens. (Theindicator turns yellow in the presenceof an acid; when carbon dioxide isproduced by the yeast, carbonic acidis formed in the water.) VisualTAKS 2 Bio 4B; TAKS 4 IPC 9B (grade 11only)

LS


Muscle Fatigue andEndurance TrainingTAKS 2 Bio 4B, 10A, 10B (grade 11only); Bio 11C

Teaching Strategies Choose a student volunteerwho is willing to do a muscleendurance test. Have the stu-dent squat with their backagainst the wall until theirthighs are parallel to the floor.They should hold this positionuntil it becomes too uncomfort-able. Ask the class to explainwhy the student could notmaintain the position forhours? (The muscles were work-ing continuously until they werefatigued and depleted of oxygen.)

DiscussionWhy are endurance athletes ableto exercise longer than non-athletes are? (One reason is theirmuscles are conditioned to obtainATP through aerobic respirationlonger than non-athletes. Aerobicrespiration fuels muscles moreefficiently than fermentation.)In what form is glucose storedin muscle tissue? (Glycogen.Glycogen reserves are depletedmore slowly in trained athletesthan non-athletes.)

Alcoholic FermentationIn other organisms, the three-carbon pyruvate is broken down toethanol (ethyl alcohol), a two-carbon compound, through alcoholic fer-mentation. Carbon dioxide is released during the process. As shown inFigure 15, alcoholic fermentation is a two-step process. First, pyruvateis converted to a two-carbon compound, releasing carbon dioxide.Second, electrons are transferred from a molecule of NADH to the two-carbon compound, producing ethanol. As in lactic acid fermentation,NAD� is recycled, and glycolysis can continue to produce ATP.

Alcoholic fermentation by yeast, a fungus, has been used in thepreparation of many foods and beverages. Wine and beer containethanol made during alcoholic fermentation by yeast. Carbondioxide released by the yeast causes the rising of bread dough andthe carbonation of some alcoholic beverages, such as beer. Ethanolis actually toxic to yeast. At a concentration of about 12 percentethanol kills yeast. Thus, naturally fermented wine contains about12 percent ethanol.

www.scilinks.orgTopic: FermentationKeyword: HX4080

Muscle Fatigue and Endurance Training

nyone who runs or exercisesfor a long period of time

soon learns about muscle fatigue.As you continue vigorous exer-cise, the muscles you are usingbecome fatigued—that is, tiredand less able to generate force.The reasons for muscle fatigue arenot fully understood, but in mostcases the fatigue increases whenthe production of lactic acid bythe exercising muscle increases.

Anaerobic ThresholdWhy does an exercising muscleproduce lactic acid? A restingmuscle obtains most of its energyfrom aerobic respiration. A con-tinuously exercising muscle, how-ever, soon depletes its availableoxygen. At this point, called theanaerobic threshold, the exercis-ing muscle begins to obtain theATP needed anaerobically. In theabsence of oxygen, glycolysisextracts the required ATP fromglycogen in the muscle. Glycogen

is a storable form of glucosethat acts as an energy reserve.Glycolysis converts the muscleglycogen to pyruvate, which isthen fermented to lactic acid.

The ability to perform con-tinuous exercise is limited bythe body’s stored glycogen. So,physical endurance can increaseif glycogen stored in muscles isspared during exercise. Trainedathletes such as cyclist LanceArmstrong, shown at right, get arelatively large portion of theirenergy from aerobic respiration.Thus, their muscle glycogenreserve is depleted more slowlythan that in untrained individuals.In fact, the greater the level ofphysical training, the higher theproportion of energy the bodyderives from aerobic respiration.

Athletic EnduranceEndurance-trained athletes gen-erally have more muscle massthan untrained people. But it is

endurance-trained athletes’ highaerobic capacity—rather thantheir greater muscle mass—thatallows these athletes to exercisemore before lactic acid produc-tion and glycogen depletioncause muscle fatigue.

www.scilinks.orgTopic: Anaerobic ThresholdKeyword: HX4192

A

Lance Armstrong

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Teaching TipATP Production Tell students thatup to 36 molecules of ATP can beproduced from a single glucosemolecule during aerobic respira-tion. Have students calculate howmuch more efficient aerobic respi-ration is than glycolysis, whichyields only two ATP molecules. (36 ATP /2 ATP � 18 times moreefficient.) Logical TAKS 2 Bio 4B;Bio 9A, 9B

ReteachingAssign students to cooperativepairs. Have each pair evaluate thefollowing scenario: Suppose youare an organism that can carry outeither aerobic respiration or anaer-obic energy pathways. Which onewould be more beneficial to you,and why? (If oxygen is present, aer-obic respiration is more beneficialbecause more ATP can be produced.)

Quiz1. During glycolysis, glucose is

broken down to ________. (pyruvate)

2.True or false: When oxygen isnot present, a small amount ofATP is still made during theKrebs cycle. (False. The Krebscycle produces ATP in the presenceof oxygen.) TAKS 2 Bio 4B

TAKS 2 Bio 4B

GENERAL

Bio 9BCo-op Learning

CloseClose

LS



1. Pyruvate: if oxygen is present, pyruvate willenter the Krebs cycle; if oxygen is absent, pyruvate will undergo fermentation. NADH: ifoxygen is present, NADH will enter the elec-tron transport chain. ATP: temporarily storesenergy for cellular processes

2. The Krebs cycle produces electron carriers thatdonate electrons to the electron transport chain.The electron transport chain produces most ofthe ATP that is produced in cellular respiration.

3. Fermentation recycles NAD+, which is neededto continue ATP production in the absence ofoxygen. TAKS 2 Bio 4B

TAKS 2 Bio 4B

TAKS 2 Bio 4B

4. If oxygen is present, aerobic respiration canoccur. Aerobic respiration produces much moreATP than anaerobic processes.

5. Sensors in the body monitor the level of glu-cose in the blood. When the blood glucose levelis high, the storage of glycogen is stimulated.When the blood glucose level is low, glucose isreleased back into the blood.

6. A. Correct. B. Incorrect.Glycolysis is an anaerobic process. C. Incorrect.Alcoholic fermentation is an anaerobic process.D. Incorrect. Lactic acid fermentation is ananaerobic process. Bio 9B

TAKS 2 Bio 4B

TAKS 2 Bio 4B


English Language Learners

Production of ATPThe total amount of ATP that a cell is able to harvest from each glucosemolecule that enters glycolysis depends on the presence or absence ofoxygen. As shown in Figure 16, cells use energy most efficiently whenoxygen is present. In the first stage of cellular respiration, glucose isbroken down to pyruvate during glycolysis. Glycolysis is an anaerobicprocess, and it results in a net gain of two ATP molecules. In the sec-ond stage of cellular respiration, the pyruvate passes through eitheraerobic respiration or (anaerobic) fermentation. When oxygen ispresent, aerobic respiration occurs. When oxygen is not present,fermentation occurs instead. The NAD� that gets recycled during fer-mentation allows glycolysis to continue producing ATP. Thus, a smallamount of ATP is produced even during fermentation. Most of a cell’sATP is made, however, during aerobic respiration. For each moleculeof glucose that is broken down, as many as two ATP molecules aremade directly during the Krebs cycle, and up to 34 ATP molecules are produced later by the electron transport chain.

Most ATP is produced during aerobic respiration.

Figure 16 Effect of oxygen on ATP production

Anaerobic processes Aerobic respiration

Glucose

Pyruvate

LactateEthanoland CO2 (Up to)

Without O2 With O2

Glycolysis

Krebs cycleFermentation

Electrontransport

chain

2 ATP(Net)

2 ATP

34 ATP

List the products of glycolysis. What is the role of each of these products in cellular respiration? 4B

Summarize the roles of the Krebs cycle and the electron transport chain during aerobicrespiration. 4B

Describe the role of fermentation in the secondstage of cellular respiration. 4B

Critical Thinking Comparing FunctionsExplain why cellular respiration is more efficientwhen oxygen is present in cells. 4B

Critical Thinking Inferring ConclusionsExcess glucose in your blood is stored in yourliver as glycogen. How might your body senseswhen to convert glucose to glycogen and glyco-gen back to glucose?

When oxygen is present, most of the ATP made in cellular respiration isproduced by 9B

A aerobic respiration. C alcoholic fermentation. B glycolysis. D lactic acid fermentation.


Section 3 Review

4B

110

Student Edition TAKS Obj 2 Bio 4B TAKS Obj 4 IPC 7D TAKS Obj 4 IPC 8A TAKS Obj 4 IPC 9B TEKS Bio 4B; TEKS IPC 7D, 8A, 9B

Teacher Edition TAKS Obj 2 Bio 4B TEKS Bio 4B, 9A, 9B

pp. 110–111

Alternative AssessmentHave each student write a questionon an index card based on theinformation presented in this chap-ter. Each student should also recordan answer to the question on a sec-ond index card. Have studentstrade question cards with a partnerand try to answer their partner’squestions. Then have them conferwith each other about theiranswers. Encourage students torefer to the textbook to settle anydisagreements.


• Science Skills Worksheet• Critical Thinking Worksheet• Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


Answer to Concept Map

The following is one possible answer to Performance Zone item 15. is stored during

Energy

which includes

which requires

is harvested during

cellular respiration

fermentation

Krebs cycle

glycolysis

photosynthesis

electron transport chain

which includes

Calvin cycle

electron transport chain

NADH

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONEKey Terms

Section 1photosynthesis (94)autotroph (94)heterotroph (95)cellular respiration (95)

Section 2pigment (98)chlorophyll (98)carotenoid (98)thylakoid (99)electron transport chain (100)NADPH (101)carbon dioxide fixation (102)Calvin cycle (102)

Section 3aerobic (104)anaerobic (104)glycolysis (105)NADH (105)Krebs cycle (106)FADH2 (107)fermentation (108)

BIOLOGYBIOLOGYUnit 2, Unit 3—Use Topics 1–6 in these units toreview the key concepts and terms in this chapter.

Energy and Living Things

● Energy from sunlight flows through living systems, fromautotrophs to heterotrophs.

● Photosynthesis and cellular respiration form a cyclebecause one process uses the products of the other.

● ATP supplies cells with energy needed for metabolism.

Photosynthesis

● Photosynthesis has three stages. First, energy is capturedfrom sunlight. Second, energy is temporarily stored in ATPand NADPH. Third, organic compounds are made usingATP, NADPH, and carbon dioxide.

● Pigments absorb light energy during photosynthesis.● Electrons excited by light travel through electron transport

chains, in which ATP and NADPH are produced.● Through carbon dioxide fixation, often by the Calvin cycle,

carbon dioxide in the atmosphere is used to make organiccompounds, which store energy.

● Photosynthesis is directly affected by environmental factorssuch as the intensity of light, the concentration of carbondioxide, and temperature.

Cellular Respiration

● Cellular respiration has two stages. First, glucose is brokendown to pyruvate during glycolysis, making some ATP.Second, a large amount of ATP is made during aerobicrespiration. When oxygen is not present, NAD+ is recycledduring the anaerobic process of fermentation.

● The Krebs cycle is a series of reactions that produceenergy-storing molecules during aerobic respiration.

● During aerobic respiration, large amounts of ATP are madein an electron transport chain.

● When oxygen is not present, fermentation follows glycolysis,regenerating NAD+ needed for glycolysis to continue.

3

2

1

111

IPC BenchmarkReview

To prepare students for the TAKS, havestudents review the periodic table ofelements on pp. 1046–1047 andProperties of Matter: ChemicalBehavior of Elements and BalancedChemical Equations TAKS Obj 4 IPC 7Don pp. 1050–1051 of the IPC Refresher inthe Texas Assessment Appendix of thisbook.

ANSWERS

Using Key Terms

1. b Bio 4A2. d TAKS 2 Bio 4B3. c TAKS 2 Bio 4B4. a5. a. An autotroph uses the energy

in sunlight or inorganic sub-stances to make organic compounds. A heterotrophmust eat food to get energy.

b. Glycolysis is the first stage ofcellular respiration. Whenoxygen is not present, fermen-tation recycles NAD+, whichallows glycolysis to continue.

c. Chlorophyll is the primarypigment of photosynthesis.Chlorophyll reflects green lightand absorbs blue and red light.Carotenoids are pigments thatreflect yellow and orange lightand absorb mostly blue andgreen light.

d. In aerobic conditions, oxygenis present. In anaerobic condi-tions, oxygen is absent. TAKS 2Bio 4B

Understanding Key Ideas

6. c TAKS 3 Bio 9D7. a Bio 9B8. d TAKS 2 Bio 4B9. b TAKS 2 Bio 4B

10. a TAKS 2 Bio 4B11. The structures are thylakoids.

During photosynthesis, hydrogenions are more concentrated insidethe thylakoids. TAKS 2 Bio 4B

12. The energy flow begins with sun-light. Autotrophs create organiccompounds using energy fromsunlight, storing some of thisenergy in their tissues as carbohy-

drates. Humans get energy by eating theautotrophs or by eating other heterotrophsthat first ate autotrophs. TAKS 2 Bio 4B

13. At the anaerobic threshold, the muscle cellshave depleted the available oxygen and resortto glycolysis and lactic acid fermentation toobtain ATP. Fatigue and cramping can result.TAKS 2 Bio 4B

14. Starch is composed of hundreds of glucosemolecules. It is broken down by enzymes,such as amylase, yielding maltose. Maltoseconsists of two glucose molecules and is bro-ken down by the enzyme maltase.

15. The answer to the concept map is on the bottom of the Study Zone page. TAKS 3 Bio 9D

TAKS 2 Bio 4B


CHAPTER 5

Section Questions1 5a, 6, 122 1, 2, 5c, 8, 9, 11, 17, 213 3, 4, 5b, 5d, 7, 10, 13, 14, 15, 16–22

Assignment Guide

PerformanceZONE

CHAPTER REVIEW

Using Key Terms1. A pigment that causes a plant to look

green isa. carotenoid. c. NADH. b. chlorophyll. d. NAPH.

2. The electron transport chains of photo-synthesis produces a. pyruvate. c. glucose. b. water. d. ATP and NADPH.

3. Most of the ATP made during cellularrespiration is produced ina. glycolysis. b. the Krebs cycle.c. mitochondria.d. fermentation.

4. Aerobic respiration involves all of thefollowing excepta. glycolysis. b. the Krebs cycle.c. mitochondria.d. ATP.

5. For each pair of terms, explain thedifference in their meanings. a. autotroph and heterotrophb. glycolysis and fermentationc. chlorophyll and carotenoidd. aerobic and anaerobic

Understanding Key Ideas6. Energy flows through living systems

from? a. the sun, to heterotrophs, and

then to autotrophs. b. autotrophs, to the environment, and

then to heterotrophs. c. the sun, to autotrophs, and then to

heterotrophs. d. the environment, to heterotrophs, and

then to autotrophs.

7. The products of photosynthesis that begincellular respiration are a. organic compounds and oxygen. b. carbon dioxide and water. c. NADP+ and hydrogen. d. ATP and water.

8. The thylakoid membranes of a chloroplastare the sites wherea. electron transport chains operate. b. NADPH and ATP are produced.c. pigments are located.d. all of the above

9. The oxygen produced during photo-synthesis comes directly from thea. splitting of carbon dioxide molecules. b. splitting of water molecules. c. mitochondrial membranes. d. absorption of light.

10. Which of the following is the correct pairingof a process and its requirement for oxygen?a. glycolysis: no oxygen requiredb. fermentation: oxygen requiredc. Krebs cycle: no oxygen requiredd. none of the above

11. Study the micrograph of a chloroplast shownbelow, and identify the structures labeled X.During photosynthesis, are hydrogen ionsmore concentrated in these structures or inthe spaces around them?

12. Analyze the flow of energy that enables you toget energy from the food you eat.

13. What change occurs inmuscles at the anaerobic threshold?

14. How is starch broken down to glucoseprior to glycolysis? (Hint: See Chapter 2,Section 4.)

15. Concept Mapping Make a conceptmap that shows how photosynthesis and cel-lular respiration are related. Try to includethe following terms in your map: glycolysis,Krebs cycle, electron transport chain, Calvincycle, fermentation, and NADH.

X

4A

4B

4A 4B

4A 4B

4B

4B

4B

4B

4B

9D

4B

4B

9D

9B

112

Review and AssessTAKS Obj 1 IPC 3ATAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 2 Bio 4B TAKS Obj 3 Bio 9D, 13ATEKS Bio 3A, 3D, 3E, 4A, 4B, 9B, 9DTEKS Bio/IPC 2C, 2D

pp. 66–67

Critical Thinking

16. Humans must obtain thiaminefrom the foods they eat. Insuffi-cient thiamine in cells maydecrease the efficiency of aerobicrespiration.

17. Answers will vary, but studentsshould acknowledge that photo-synthetic organisms today carryout photosynthesis in the pres-ence of oxygen.

18. In photosynthesis, energy fromthe sun excites electrons in thepigments of the thylakoid mem-branes. The excited electrons are passed along the electrontransport chain, setting up a con-centration gradient of hydrogenions. This gradient is used tomake ATP. The process is similarin cellular respiration, but NADHis the original source of electrons,and the initial energy source isglucose rather than the sun.

19. More folds in the mitochondrialinner membrane would providemore surface area for cellular respiration, increasing theamount of cellular respirationthat can occur.

Alternative Assessment

20. Answers will vary. Bacteria areused to make yogurt, sour cream,and some cheeses. Other cheesesare made with the help of fungi.During bread making, alcoholicfermentation by yeast producesalcohol, which evaporates, andcarbon dioxide, which makes thebread rise.

21. Answers will vary. Enzymologistsstudy the structure and function ofenzymes and the effects of enzymedeficiencies. The career requiresbachelors and advanced degrees inchemistry or biology. Employersinclude universities and companiessuch as chemical and pharmaceuti-cal manufacturers. Growthprospects are good. Starting salarywill vary by region.

22. Answers will vary. The diet of anathlete depends on the energyrequirements of the athlete’ssport. Some sports, such asweight lifting, involve mainlyanaerobic metabolism. Others,such as jogging and swimminginvolve aerobic respiration.

Bio 3D

Bio 9B

TAKS 1 IPC 3A; Bio 3A

Standardized Test Prep1. A. Correct. Graph shows no photosynthesis at

0ºC. B. Incorrect. Optimum temperature forphotosynthesis is between 20–25ºC. C. Incorrect.Rate at 40ºC is less than at 20ºC. D. Incorrect.The rate decreases from 25ºC to 30ºC.

2. F. Incorrect. At 0ºC there is no photosynthesisoccurring. G. Correct. 23ºC is the optimumtemperature for photosynthesis, which pro-duces oxygen. H. Incorrect. At 46ºC very littlephotosynthesis is occurring. J. Incorrect. At50ºC there is no photosynthesis occurring.TAKS 1 Bio/IPC 2C

TAKS 1 Bio/IPC 2D

3. A. Incorrect. Photosynthesis would not occur atlow temperatures. B. Incorrect. Photosynthesiswould not occur at low temperatures.C. Incorrect. Plant would require higher tem-peratures for optimum rates of photosynthesis.D. Correct. Plant would be adapted for photo-synthesis at higher temperatures. TAKS 3 Bio 13A


Test

The chart below shows data on photosynthesisin one type of plant. Use the chart and yourknowledge of science to answer questions 1–3.

1. Which statement is supported by the data?A Photosynthesis does not occur at 0°C. B The optimum temperature for photo-

synthesis is approximately 46°C.C The rate of photosynthesis at 40°C is

greater than the rate at 20°C.D The rate of photosynthesis increases as

temperature increases from 25°C to 30°C.

2. At approximately what temperature is the plant producing oxygen at the greatestrate? F 0°C H 46°CG 23°C J 50°C

3. Data obtained from a different type of plant show a similar relationship betweenrate of photosynthesis and temperature, but the curve is shifted to the right. Whatenvironment would this plant be bestadapted to?A Cold subarctic environmentB Cool, wet environmentC Mild, dry environmentD Hot equatorial environment


100 20 30 40 50

Rate

of

photo

synth

esi

s

Temperature (°C)

Effect of Temperature on Photosynthesis

Critical Thinking16. Distinguishing Relevant Information The

enzyme that aids in the conversion of pyru-vate to acetyl-CoA requires vitamin B1, alsocalled thiamine. Thiamine is not made inthe human body. How would a deficiency ofthiamine in cells affect cellular respiration?

17. Evaluating Viewpoints State whether youthink the following viewpoint can be sup-ported, and justify your answer. “If Earth’searly atmosphere had been rich in oxygen,photosynthetic organisms would not havebeen able to evolve.”

18. Evaluating Differences Compare theenergy flow in photosynthesis to the energyflow in cellular respiration.

19. Inferring Relationships How might thefolding of the inner membrane of mito-chondria affect the rate of aerobic respiration? Explain your answer.

Alternative Assessment20. Analyzing Methods Research several ways

that fermentation is used in food prepara-tion. Find out what kinds of microorganismsare used in cultured dairy products, such asyogurt, sour cream, and some cheeses.Research the role of alcoholic fermentationby yeast in bread making. Prepare an oralreport to summarize your findings.

21. Career Connection Enzymologist Researchthe educational background necessary tobecome an enzymologist. List the coursesrequired, and describe additional degrees ortraining that are recommended for thiscareer. Write a report on your findings.

22. Interactive Tutor Unit 2 Photosynthesis,Unit 3 Cellular Respiration Write a reportsummarizing how exercise physiologistsregulate the diet and training of athletes.Find out how diet varies according to theneeds of each athlete. Research the rela-tionship between exercise and metabolism.

Before choosing an answer to a question, try toanswer the question without looking at the answerchoices on the test.

9B

2C

13A

2D

3D

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3A

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