81 Energy and Life ??1 Energy and Life 1 FOCUS Objectives 8.1.1 Explain where plants get the energy they need to produce food. 8.1.2 Describe the role of ATP in cellular activities. Vocabulary Preview Explain that the term autotroph comes from, ...

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Figure 81 Autotrophsuse light energy from thesun to produce food. Theseimpalas get their energy by eating grass, while thisleopard gets its energy byeating impalas and otheranimals. Impalas and leop-ards are both heterotrophs. Energy is the ability to do work. Nearly every activity in modern society depends on one kind of energy or another.When a car runs out of fuelmore precisely, out of the chemicalenergy in gasolineit comes to a sputtering halt. Without electrical energy, lights, appliances, and computers stop working.Living things depend on energy, too. Sometimes, the need forenergy is easy to see. It is obvious that energy is needed to playsoccer or other sports. However, there are times when that needis less obvious. For example, when you are sleeping, your cellsare busy using energy to build new proteins and amino acids.Clearly, without the ability to obtain and use energy, life wouldcease to exist.Autotrophs and HeterotrophsWhere does the energy that living things need come from? Thesimple answer is that it comes from food. Originally, though, theenergy in most food comes from the sun. Plants and someother types of organisms are able to use light energy fromthe sun to produce food. Organisms such as plants, whichmake their own food, are called (AW-toh-trohfs).Other organisms, such as animals, cannot use the sunsenergy directly. These organisms, known as (HET-uh-roh-trohfs), obtain energy from the foods they consume.Impalas, for example, eat grasses, which are autotrophs. Otherheterotrophs, such as the leopard shown in Figure 81, obtainthe energy stored in autotrophs indirectly by feeding on animalsthat eat autotrophs. Still other heterotrophsmushrooms, forexampleobtain food by decomposing other organisms. To live,all organisms, including plants, must release the energy insugars and other compounds.heterotrophsautotrophsKey Concepts Where do plants get theenergy they need to producefood? What is the role of ATP incellular activities?Vocabularyautotrophheterotrophadenosine triphosphate (ATP)Reading Strategy: Asking Questions Beforeyou read, study the diagram inFigure 83. Make a list ofquestions that you have aboutthe diagram. As you read, writedown the answers to yourquestions.81 Energy and Life1 FOCUSObjectives8.1.1 Explain where plants get theenergy they need to producefood.8.1.2 Describe the role of ATP incellular activities.Vocabulary PreviewExplain that the term autotrophcomes from the Greek words autos,meaning self, and trophe, meaningfood. Therefore, an autotroph is anorganism that makes food for itself.Ask: If heteros means other, whatdoes heterotroph mean? (A hetero-troph is an organism that gets foodfrom others.)Reading StrategyHave students write a question foreach head and subhead. For exam-ple, they might ask, What areautotrophs and heterotrophs? Asstudents read the section, encouragethem to write the answer to eachquestion. Students can use theirquestions and answers as a studyguide.2 INSTRUCTAutotrophs andHeterotrophsBuild Science SkillsClassifying Divide the class intosmall groups and have each groupbrainstorm a list of types of livingthings. Then, ask the groups to classi-fy each type of living thing accordingto whether it is an autotroph or aheterotroph. After the groups havemade their classifications, askwhether they found it difficult to classify any type of organism. Somestudents may know that certain bacteriachemoautotrophsareclassified as autotrophs but do notobtain energy from the sun.Photosynthesis 201Section 81SECTION RESOURCESPrint: Teaching Resources, Lesson Plan 81,Adapted Section Summary 81, AdaptedWorksheets 81, Section Summary 81,Worksheets 81, Section Review 81 Reading and Study Workbook A, Section 81 Adapted Reading and Study Workbook B,Section 81Technology: iText, Section 81 Animated Biological Concepts DVD, 8 ATPFormation Transparencies Plus, Section 81TimeSaver0200_0214_bi_c07_te 3/7/06 10:26 PM Page 201Chemical Energy and ATPEnergy comes in many forms, including light, heat, and electric-ity. Energy can be stored in chemical compounds, too. For exam-ple, when you light a candle, the wax melts, soaks into the wick,and is burned, releasing energy in the form of light and heat. Asthe candle burns, high-energy chemical bonds between carbonand hydrogen atoms in the wax are broken. The high-energybonds are replaced by low-energy bonds between these atomsand oxygen. The energy of a candle flame is released from elec-trons. When the electrons in those bonds are shifted from higherenergy levels to lower energy levels, the extra energy is releasedas heat and light.Living things use chemical fuels as well. One of the principalchemical compounds that cells use to store and release energy is(uh-DEN-uh-seen try-FAHS-fayt),abbreviated As Figure 82 shows, ATP consists of adenine,a 5-carbon sugar called ribose, and three phosphate groups.Those three phosphate groups are the key to ATPs ability tostore and release energy.Storing Energy Adenosine diphosphate (ADP) is a compoundthat looks almost like ATP, except that it has two phosphategroups instead of three. This difference is the key to the way inwhich living things store energy. When a cell has energy avail-able, it can store small amounts of it by adding a phosphategroup to ADP molecules, producing ATP, as shown in Figure 83.In a way, ATP is like a fully charged battery, ready to power themachinery of the cell.Releasing Energy How is the energy that is stored in ATPreleased? Simply by breaking the chemical bond between thesecond and third phosphates, energy is released. Because a cellcan subtract that third phosphate group, it can release energyas needed. ATP has enough energy to power a variety of cellularactivities, including active transport across cell membranes,protein synthesis, and muscle contraction. The character-istics of ATP make it exceptionally useful as the basicenergy source of all cells.What is the difference between ATP and ADP?Using Biochemical EnergyOne way cells use the energy provided by ATP is to carry out activetransport. Many cell membranes contain a sodium-potassiumpump, a membrane protein that pumps sodium ions (Na+) out ofthe cell and potassium ions (K+) into it. ATP provides the energythat keeps this pump working, maintaining a carefully regulatedbalance of ions on both sides of the cell membrane. ATP producesmovement, too, providing the energy for motor proteins that moveorganelles throughout the cell.ATP.adenosine triphosphate Figure 82 ATP is used byall types of cells as their basicenergy source. The energy neededby the cells of this soccer playercomes from ATP.P P PAdenine 3 Phosphate groupsRiboseATPFor: ATP activityVisit: PHSchool.comWeb Code: cbd-3081202 Chapter 8Chemical Energyand ATPAddress MisconceptionsSome students may have difficultywith the concept that naturalprocesses occur automatically whenmaterials and conditions are right.Ask: Do cells think about the lifeprocesses they carry out? (Somestudents might suggest that the nucle-us is the brain of the cell, so maybethe nucleus directs cell processes in thesame way a human brain directs bodymovements.) Point out that cells haveno thoughts. Although we oftenspeak of how a cell uses energy orof how a cell can add a phosphategroup, these words should not sug-gest that cells decide when or howto act.Use VisualsFigure 82 Ask: What does an ATPmolecule consist of? (Adenine,ribose, and three phosphate groups)What do the lines between theseparts of the molecule represent?(Chemical bonds) What would bethe result if the third phosphategroup were removed? (The remain-ing molecule would be ADP, andremoving the third phosphate groupwould release energy.)Make ConnectionsChemistry Use a large spring tohelp students understand the releaseof energy that occurs when the thirdphosphate group of ATP is removed.Explain that the tail of three phos-phate groups is unstable and that thebonds that hold the phosphategroups together have high potentialenergy. In a sense, they are like acompressed spring. The chemicalchange that occurs when a phos-phate group is removed and newproducts are formed is like lettingthat spring go. Energy is released asthe spring relaxesthat is, as thespring changes from an unstable con-dition to a more stable condition.Comprehension: Prior KnowledgeBeginning To help students understand theconcept of energy, show photos of people doingstrenuous activities, e.g., running, loading mov-ing vans. As you show each photo, brieflydescribe how energy is being used, for example,Legs need energy to move. Pair beginning stu-dents with English-proficient students, and havethe pairs identify other activities that requireenergy. Have the pairs explain aloud how energy is used in their examples.Intermediate Write the following sentence onthe board and read it aloud: Cells need ener-gy to do work. Call on volunteers to explainwhat energy means. Explain how the conceptof energy relates to cells. Then, have studentsuse what they learned in Chapter 7 to writelists of some cellular activities that requireenergy. Ask individual students to explain howthese processes use energy.SUPPORT FOR ENGLISH LANGUAGE LEARNERS81 (continued)Your students can extend theirknowledge of ATP through thisonline experience.0200_0214_bi_c07_te 3/7/06 10:26 PM Page 202Photosynthesis 203Answers to . . . ATP has three phos-phate groups; ADP has two.Figure 83 ADP is formed, andstored energy is released.81 Section Assessment1. The sun2. ATP stands for adenosine triphosphate, whichis one of the principal chemical compoundsthat living things use to store energy andrelease it for cell work to be done.3. A typical answer might mention active trans-port, movements within the cell, synthesis ofproteins and nucleic acids, or responses tochemical signals.4. Autotrophs obtain energy by making theirown food. Heterotrophs obtain energy fromthe foods they consume.5. Similar: Both store chemical energy for a cell.Different: A single molecule of glucose storesmore than 90 times the chemical energy ofan ATP molecule.Adenosine Diphosphate (ADP) + Phosphate Adenosine Triphosphate (ATP) +EnergyEnergyADPP PPP P PPartially charged batteryFully chargedbatteryATPEnergy from ATP powers other important events in the cell,including the synthesis of proteins and nucleic acids and responsesto chemical signals at the cell surface. The energy from ATP caneven be used to produce light. In fact, the blink of a firefly on asummer night comes from an enzyme powered by ATP!ATP is such a useful source of energy that you might thinkthe cells would be packed with ATP to get them through the day,but this is not the case. In fact, most cells have only a smallamount of ATP, enough to last them for a few seconds of activity.Why? Even though ATP is a great molecule for transferringenergy, it is not a good one for storing large amounts of energyover the long term. A single molecule of the sugar glucose storesmore than 90 times the chemical energy of a molecule of ATP.Therefore, it is more efficient for cells to keep only a smallsupply of ATP on hand. Cells can regenerate ATP from ADP asneeded by using the energy in foods like glucose. As you will see,thats exactly what they do. Figure 83 ATP can be com-pared to a fully charged batterybecause both contain stored energy,whereas ADP resembles a partiallycharged battery. Predicting Whathappens when a phosphate group isremoved from ATP?1. Key Concept What is theultimate source of energy forplants?2. Key Concept What is ATPand what is its role in the cell? 3. Describe one cellular activity thatuses the energy released by ATP.4. How do autotrophs obtainenergy? How do heterotrophsobtain energy?5. Critical Thinking Comparingand Contrasting With respectto energy, how are ATP andglucose similar? How are theydifferent?81 Section AssessmentInterdependence inNature Recall that energyflows and that nutrients cyclethrough the biosphere. Howdoes the process of photosyn-thesis impact the flow ofenergy and the cycling ofnutrients? You may wish torefer to Chapter 3 to help youanswer this question.Using BiochemicalEnergyBuild Science SkillsUsing Analogies Some studentsmay have difficulty understandingwhy cells keep only a small supply ofATP on hand. To clarify, displaynumerous coins and a number ofpaper bills of varying denominations.Explain that molecules of ATP are likethe coinscoins are very useful, buttoo many of them fill a pocket fast.The paper money is like glucosethe bills represent much more valuethan an equal mass of coins.3 ASSESSEvaluate UnderstandingCall on students at random toexplain the difference betweenautotrophs and heterotrophs. Then,ask other students to explain the dif-ference between ATP and ADP,describe how cells store and releaseenergy, and explain why cells con-tain only a small amount of ATP.ReteachHave pairs of students work togetherto make a sequence of labeled illus-trations that show how energy isstored and released through theaddition and removal of a phosphategroup. If your class subscribes to the iText,use it to review the Key Concepts inSection 81.Producers are essential to theflow of energy through the bio-sphere, since they help beginthat flow. Photosynthesis is alsoimportant in the carbon cycle.Plants and other photosyntheticorganisms take in carbon dioxideand use the carbon to build carbohydrates.0200_0214_bi_c07_te 3/7/06 10:26 PM Page 2030201_bi_c07_teCA.pdf0202_bi_c07_teCA.pdf0203_bi_c07_teCA.pdf


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