AP Environmental Science
PROFESSIONAL DEVELOPMENTAP EnvironmentalScienceEcologySpecial Focus08-1453.AP.SF.EnvSciences.indd 18/15/08 4:21:00 PM
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Contents1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Scottie Smith2. Ecosystem Energy Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Carol Widegren3. Ecosystem Structure and the Role of Species Within Biomes . . . . . . . . . . 11Kathryn Weatherhead4. Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Mark Ewoldsen5. Community Interactions and Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Sarah Utley6. Ecological Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Pam Schlachtman7. About the Editor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918. About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91iii08-1453.AP.SF.EnvSciences.indd 38/15/08 4:21:00 PM
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IntroductionScottie SmithCanterbury School of FloridaSt. Petersburg, FloridaOne of the essential underpinnings of a course in environmental science is abasic understanding of ecology. The irony lies in the nature of the two courses.Environmental science is an introductory college course and is often a collegestudent’s first foray into the natural sciences arena. However, ecology is typically anupper-level course at most colleges and universities, requiring numerous introductorycourses prior to enrollment. Ecology is the relationship between organisms—atthe individual, species, population, community, and ecosystem level—and theirenvironment. In order to understand environmental science, which is basically thehuman impact on these organisms and their interactions, one must grasp conceptsthat are actually quite difficult for the budding scientist. Therefore, a special focusdevoted to ecology seemed prudent, particularly since both multiple-choice andfree-response questions on the AP Environmental Science Exam will directly andperipherally address concepts of ecology.In this Special Focus publication, teachers will be provided with discussionand pertinent examples of numerous ecological precepts. The first section containsan introduction to energy, including photosynthesis, cellular respiration, and mattercycling and energy flow through ecosystems. This section is paramount to anunderstanding of AP Environmental Science and actually addresses one of the majorthemes of the course: Energy conversions underlie all ecological processes. Pertinentinformation is provided regarding trophic levels, food webs, and ecological pyramids.Another section discusses primary productivity because it potentiates the complexnature of the niche structure and therefore impacts the biodiversity of ecosystems.Special instruction is given to the terminologies used for species within variousniche structures. An entire section is devoted to discussing the evolution, naturalselection, adaptation, and interactions of species. The evolution section addresses08-1453.AP.SF.EnvSciences.indd 18/15/08 4:21:01 PM
Special Focus:Ecologyanother of the themes—that Earth is one interconnected system—upon which the APEnvironmental Science course is based. Finally, there is a discussion of communityinteractions, including succession, disturbance, resilience, stability, edge effect,and island biodiversity. Numerous exercises have been produced for this SpecialFocus publication, including adaptation and natural selection labs, succession,primary productivity, and ecological footprint and Shannon-Weiner biodiversity indexcalculations.Since students have traditionally had difficulty with the variety of calculationsrequired on the AP Environmental Science Exam, many different types of calculationsand exercises have been included in this guide. It is hoped that students will masterand acheive confidence in their mathematical skills after they have sufficient practiceto increase their proficiency. Calculations are required not only in the multiple-choiceportion of a typical AP Environmental Science Exam; sometimes the free-responsesection incorporates several different calculations so that the questions can beanswered fully.208-1453.AP.SF.EnvSciences.indd 28/15/08 4:21:01 PM
Ecosystem Energy Flow: An Introductionto Energy and Laws of ThermodynamicsCarol WidegrenLincoln Park High SchoolChicago, IlliniosAlthough students entering an AP Environmental Science class have taken previousscience classes, generally they do not have an understanding of the role that energyhas in their biological environment.In high school physics class, students are usually taught to define energy as theability to do work, which might be expressed as a force moving through a distance.They are further taught that energy may be either kinetic (an energy associatedwith motion) or potential (an energy associated with position). They may encounterenergy in mechanical, heat, light, and electrical form, among others. When studyingkinematics, they learn that not all of the energy put into a system results in usefulenergy; some is converted to heat due, for example, to friction. This phenomenonleads to an understanding that energy cannot be created or destroyed but can betransformed from one form to another.Often neither chemistry nor physics courses include a discussion about theenergy necessary to hold together the parts composing atoms or the energy requiredby atoms to form molecules. Energy levels may be discussed in both courses, butoften a conceptual understanding of energy is not achieved. It is with this backgroundthat students enter the AP Environmental Science class.Thermodynamics, the principles that govern energy relationships, is veryimportant to an understanding of our biological environment. Such energyrelationships describe constraints on the generation of heat, the transformations ofenergy, and energy transfer within a system or to the surroundings. In other words, ifenergy is added to a system from its surroundings, it may return to the surroundingsin a different form. The first law of thermodynamics states that energy is conserved08-1453.AP.SF.EnvSciences.indd 38/15/08 4:21:01 PM
Special Focus:Ecologywhen both a system and its surroundings are considered; that is, energy can neitherbe created nor destroyed but may be transformed from one form to another, includingthe exchange of energy with its surroundings. The second law is sometimes referredto as the law of entropy. To put it simply, in any energy transformation, some energy islost as unusable energy in the sense that work cannot be performed.Any discussion of energy in an environmental science class must investigatethe two following questions: (1) Where does the energy needed for living organismsoriginate and (2) how is energy used by these organisms? At the onset of a discussionabout energy relationships, it is important for students to think of the surface of earthas a system subject to the first two laws of thermodynamics. Most of the energyadded to this system arrives on earth in the form of electromagnetic radiation fromthe sun. It has been estimated that 58 percent of the radiation directed toward earthis reflected or absorbed as heat by our atmosphere, that less than two percent ofthis remaining radiation is used by plants, and that the balance is transformed onearth’s surface into heat. Other sources of energy that should be noted include energyreleased by geothermal and volcanic activity, as well as naturally occurring nuclearreactions.Living organisms must conform to the laws of thermodynamics. Consider livingorganisms as temporary storage units for useful energy, whereby one organism canbe used by another as a source of energy. In its transfer from one organism to another,useful energy is lost to the environment in the form of heat until the useful energy isultimately consumed. As energy cannot recycle, there is a continuous requirementfor new energy to enter the system. Photosynthesizing organisms use a series ofoxidation-reduction reactions based on solar input to produce and store their owncarbohydrates, which then become the energy source for other organisms.Ecosystems and EnergyThe food consumed by an organism will undergo a number of chemical reactionsthat are collectively referred to as metabolism. Materials in addition to water aretransported across cell membranes. These processes are facilitated by carrier proteinsembedded within the membrane. The detailed transformation of nutrients is beyondthe scope of this discussion. Descriptions of these processes may be found bysearching for information on the Krebs (citric acid) Cycle. Students should understandthat organisms take in nutrients, the energy of which becomes available throughoxidation and reduction reactions.408-1453.AP.SF.EnvSciences.indd 48/15/08 4:21:01 PM
Ecosystem Energy Flow: An Introduction to Energy and Laws of ThermodynamicsExtremophiles should be briefly considered in this course. These organismslive under severe conditions; some never receive sunlight or may be found clusteredaround underwater vents producing superheated boiling water. Their source of energyis through chemosynthesis, the process in which inorganic compounds such asnitrites, hydrogen sulfide, and hydrogen gas provide the necessary energy for theseorganisms to produce their own organic food. This information is sufficient to explainchemosynthesis without going into further detail.PhotosynthesisGreen plants are able to make food by producing ATP (a carrier for energy) andNADPH (a carrier for electrons used in the synthesis of glucose) in their chloroplasts,which then reduce carbon dioxide and water to form a carbohydrate (glucose) onlyin the presence of sunlight and chlorophyll. This process is actually a complex seriesof reactions where radiant energy is transformed into chemical energy. This series ofreactions produces most of the oxygen in our atmosphere.6CO 2 6H 2O — C 6H 12O 6 6O 2carbondioxidewater light& chlorophyllglucoseoxygenCellular RespirationIn this process, carbon dioxide, water, and available energy are produced by theoxidation of glucose. This series of chemical reactions occurs in all living cells. Inaerobic organisms (those that can utilize oxygen). It is a process that requires oxygenand occurs at the cellular mitochondria; however, the first steps in the transformationof glucose take place in the cytoplasm rather than within the mitochondria and do notrequire oxygen. If the reaction never proceeds to the mitochondria, the organism hascarried out anaerobic respiration, also known as fermentation. These first processesare known as glycolysis (glucose breaking). Although heat is released in this process,some of the energy is used to replenish the supply of ATP (a carrier for energy) andNADPH (a carrier for electrons used in the synthesis of glucose).C 6H 12O 6 6O 2 — 6CO 2 6H 2OglucoseoxygencarbondioxidewaterTrophic LevelsA producer, or autotroph, is an organism that makes its own food by eitherphotosynthesis or chemosynthesis. A consumer, or heterotroph, is an organism508-1453.AP.SF.EnvSciences.indd 58/15/08 4:21:01 PM
Special Focus:EcologySTORED ENERGY DECREASESthat receives its energy from other organisms. Each step in the transfer of energy(autotroph to heterotroph and heterotroph to heterotroph) is known as a trophiclevel. The laws of thermodynamics apply to the energy flow through an ecosystem;therefore, less energy is available to organisms at each higher trophic level. Thisdecreased amount of available energy at each trophic level is due to the amountof energy required by an organism to carry out the daily functions of living. It isestimated that only 10 percent of the energy at each trophic level is available toorganisms at the next higher level.Decomposers are often overlooked when considering trophic levels. Theseorganisms receive their nutrients and energy while breaking down and recyclingorganic materials. Because their activity permits nutrients contained within deceasedFINALCONSUMERSENERGY STORED BYSECONDARY CONSUMERSENERGY STORED BYPRIMARY CONSUMERSENERGY STORED BY PRODUCERSTHE ENERGY PYRAMIDorganisms and waste products to be available to other trophic-level organisms,decomposers are important to the flow of energy and matter through the ecosystemFood Chains and WebsEnergy flow through an ecosystem may be traced through its food chain; that is, bytracking down what feasts upon what, we can follow the flow of energy. At the lowestlevel of the food chain, we find the autotrophs—organisms that manufacture theirfood by either photosynthesis or chemosynthesis. Generally, herbivores eat autotrophsand are considered “primary consumers.” Carnivores dine on the primary consumers608-1453.AP.SF.EnvSciences.indd 68/15/08 4:21:02 PM
Ecosystem Energy Flow: An Introduction to Energy and Laws of Thermodynamicsand are designated as “secondary consumers.” This, of course, is stated as thesimplest food chain. In nature, as we are well aware, nothing is quite that simple. Inan ecosystem, there are numerous food chains linked to each other to form a complex“food web.”Ecological PyramidsThe trophic structure of an ecosystem may be represented by an ecological pyramid.The base of the pyramid is composed of the producers, and each trophic level abovethe base represents consumers higher on the food chain.Pyramids may be of three types: energy, numbers, and biomass. An energypyramid shows a decreasing amount of energy available to each successive trophiclevel. This pyramidal shape is, of course, in accordance with the fact that only 10percent of the energy at each trophic level is available to organisms at the next higherlevel. A pyramid based on the number of organisms at each trophic level also reflectsenergy loss, as does a pyramid based on biomass. Because only 10 percent of theenergy at a given trophic level is available to the next higher level, food chains areusually short—usually not more than four or five links—and the number of organismsat each lower level must be greater than that of the organisms at the next higher level.Image from:soils.usda.gov/ /soil food web.htmAn example of this could be found in a forest where green plants receive their energyfrom the sun. Primary consumers might include insects, mice, and rabbits. Secondaryconsumers could be birds and snakes, while tertiary consumers include wolves andowls. Note that owls are birds—a complex food web! Omnivores (like us) should708-1453.AP.SF.EnvSciences.indd 78/15/08 4:21:02 PM
Special Focus:Ecologybe mentioned because omnivores circumvent the traditional notion of a food chainbecause they consume organisms from multiple levels.Practice Questions:1. How does the flow of energy through an ecosystem conform to the laws ofthermodynamics? Be sure to discuss its origination, transformation, and utilization.Ecosystems conform to the laws of thermodynamics. The first law ofthermodynamics states that energy is conserved; that is, energy cannotbe created or destroyed, but it may be converted from one form to another.An ecosystem is a closed system that receives energy from outsidesources; although there may be other sources, students have studiedelectromagnetic radiation from the sun. The organisms making up theecosystem transform this energy into useful forms for storage and laterutilization. Students study photosynthesis as a transformation processproducing glucose (food), which may then be accessed as an energysource for the organism. The second law of thermodynamics states thatsome energy is lost as “useless” energy. Therefore, energy enters thesystem; is converted to food, which is stored by the organism; energyis used in normal metabolic processes; and energy is dissipated to theatmosphere during the normal living processes of the organism.2. Green plants produce most of the oxygen in our atmosphere through a series ofcomplex reactions. Name and describe this generalized reaction.Green plants produce most of the oxygen in our atmosphere byphotosynthesis. The generalized reaction for this process is often referredto as “the light reaction.”6CO 2 6H 2O — C 6H 12O 6 6O 2carbondioxidewaterglucoseoxygen3. What is the role of ATP and NADPH in metabolism? What effect does the amount oflight have on the metabolism of green plants?Green plants are able to make food by producing ATP (a carrier for energy)and NADPH (a carrier for electrons used in the synthesis of glucose) intheir chloroplasts, which then reduce carbon dioxide and water to forma carbohydrate (glucose) only in the presence of sunlight and chlorophyll.808-1453.AP.SF.EnvSciences.indd 88/15/08 4:21:02 PM
Ecosystem Energy Flow: An Introduction to Energy and Laws of ThermodynamicsThe amount of light available is critical for this process (photosynthesis)to occur.BIOMASS DECREASESMASSOFCONSUMERSTOTAL MASSOF PREDATORSTOTAL MASS OF HERBIVORESTOTAL MASS OF PRODUCERSTHE BIOMASS PYRAMID4. Identify the structure shown above—be specific! What factors limit the steepnessof the sides of this structure? Explain in detail.The diagram shown above may be a biomass, energy, or numberspyramid by trophic level. As one moves higher on the pyramid, there is adecrease in biomass, energy, or numbers. Specifically, at the base level,stored energy, mass, or number of producers is greater than at the nextlevel above. This decrease continues at each trophic level, culminating inthe apex of the pyramid having the least biomass, stored energy, and/orquantity of individuals present.5. A temperate deciduous forest contains the following organisms: oak tree, pine tree,grass, mouse, rabbit, crow, hawk, mushroom, dandelion, beetle, snake. Construct afood web using at least five of these organisms. If one of the organisms used in yourweb becomes unavailable, discuss what possible effect this would have on the web.There are numerous possibilities of a food web such as: grass-mousesnake-crow-hawk. If one of the organisms becomes unavailable, the webchanges to reflect the change. The most critical
Environmental science is an introductory college course and is often a college student’s first foray into the natural sciences arena. However, ecology is typically an upper-level course at most colleges and universities, requiring numerous introductory courses prior to enrollment. Ecology is the relationship between organisms—at
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The Environmental Science End-of-Course (EOC) exam is intended to measure student proficiency of the New Mexico Science Standards. This course-level exam is provided to all students who have completed Environmental Science or related courses. This exam can be given for the following STARS course codes: 1751 – Environmental Science 1752 – AP .
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