PROFESSIONAL DEVELOPMENT AP® Environmental Science Ecology Special Focus 08-1453.indd 1 8/15/08 4:21:00 PM The College Board: Connecting Students to College Success The College Board is a not-for-profit membership association whose mission is to connect students to college success and opportunity. Founded in 1900, the association is composed of more than 5,400 schools, colleges, universities, and other educational organizations. Each year, the College Board serves seven million students and their parents, 23,000 high schools, and 3,500 colleges through major programs and services in college admissions, guidance, assessment, financial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT®, the PSAT/NMSQT®, and the Advanced Placement Program® (AP®).
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All other products and services may be trademarks of their respective owners. Visit the College Board on the Web: www.indd 2 8/15/08 4:21:00 PM Contents 1. Ecosystem Energy Flow. Ecosystem Structure and the Role of Species Within Biomes.
Community Interactions and Diversity. About the Editor. About the Authors .indd 4 8/15/08 4:21:00 PM Introduction Scottie Smith Canterbury School of Florida St. Petersburg, Florida One of the essential underpinnings of a course in environmental science is a basic understanding of ecology.
The irony lies in the nature of the two courses. 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 the individual, species, population, community, and ecosystem level—and their environment.
In order to understand environmental science, which is basically the human impact on these organisms and their interactions, one must grasp concepts that are actually quite difficult for the budding scientist. Therefore, a special focus devoted to ecology seemed prudent, particularly since both multiple-choice and free-response questions on the AP® Environmental Science Exam will directly and peripherally address concepts of ecology. In this Special Focus publication, teachers will be provided with discussion and pertinent examples of numerous ecological precepts. The first section contains an introduction to energy, including photosynthesis, cellular respiration, and matter cycling and energy flow through ecosystems.
This section is paramount to an understanding of AP Environmental Science and actually addresses one of the major themes of the course: Energy conversions underlie all ecological processes. Pertinent information is provided regarding trophic levels, food webs, and ecological pyramids. Another section discusses primary productivity because it potentiates the complex nature of the niche structure and therefore impacts the biodiversity of ecosystems. Special instruction is given to the terminologies used for species within various niche structures.
An entire section is devoted to discussing the evolution, natural selection, adaptation, and interactions of species. The evolution section addresses 08-1453.indd 1 8/15/08 4:21:01 PM Special Focus: Ecology another of the themes—that Earth is one interconnected system—upon which the AP Environmental Science course is based. Finally, there is a discussion of community interactions, including succession, disturbance, resilience, stability, edge effect, and island biodiversity. Numerous exercises have been produced for this Special Focus publication, including adaptation and natural selection labs, succession, primary productivity, and ecological footprint and Shannon-Weiner biodiversity index calculations.
Since students have traditionally had difficulty with the variety of calculations required on the AP Environmental Science Exam, many different types of calculations and exercises have been included in this guide. It is hoped that students will master and acheive confidence in their mathematical skills after they have sufficient practice to increase their proficiency. Calculations are required not only in the multiple-choice portion of a typical AP Environmental Science Exam; sometimes the free-response section incorporates several different calculations so that the questions can be answered fully.indd 2 8/15/08 4:21:01 PM Ecosystem Energy Flow: An Introduction to Energy and Laws of Thermodynamics Carol Widegren Lincoln Park High School Chicago, Illinios Although students entering an AP Environmental Science class have taken previous science classes, generally they do not have an understanding of the role that energy has in their biological environment. In high school physics class, students are usually taught to define energy as the ability 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 associated with motion) or potential (an energy associated with position). They may encounter energy in mechanical, heat, light, and electrical form, among others. When studying kinematics, they learn that not all of the energy put into a system results in useful energy; some is converted to heat due, for example, to friction. This phenomenon leads to an understanding that energy cannot be created or destroyed but can be transformed from one form to another.
Often neither chemistry nor physics courses include a discussion about the energy necessary to hold together the parts composing atoms or the energy required by atoms to form molecules. Energy levels may be discussed in both courses, but often a conceptual understanding of energy is not achieved. It is with this background that students enter the AP Environmental Science class. Thermodynamics, the principles that govern energy relationships, is very important to an understanding of our biological environment.
Such energy relationships describe constraints on the generation of heat, the transformations of energy, and energy transfer within a system or to the surroundings. In other words, if energy is added to a system from its surroundings, it may return to the surroundings in a different form. The first law of thermodynamics states that energy is conserved 08-1453.indd 3 8/15/08 4:21:01 PM Special Focus: Ecology when both a system and its surroundings are considered; that is, energy can neither be created nor destroyed but may be transformed from one form to another, including the exchange of energy with its surroundings. The second law is sometimes referred to as the law of entropy.
To put it simply, in any energy transformation, some energy is lost as unusable energy in the sense that work cannot be performed. Any discussion of energy in an environmental science class must investigate the two following questions: (1) Where does the energy needed for living organisms originate and (2) how is energy used by these organisms? At the onset of a discussion about energy relationships, it is important for students to think of the surface of earth as a system subject to the first two laws of thermodynamics. Most of the energy added to this system arrives on earth in the form of electromagnetic radiation from the sun. It has been estimated that 58 percent of the radiation directed toward earth is reflected or absorbed as heat by our atmosphere, that less than two percent of this remaining radiation is used by plants, and that the balance is transformed on earth’s surface into heat.
Other sources of energy that should be noted include energy released by geothermal and volcanic activity, as well as naturally occurring nuclear reactions. Living organisms must conform to the laws of thermodynamics. Consider living organisms as temporary storage units for useful energy, whereby one organism can be 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 is ultimately consumed.
As energy cannot recycle, there is a continuous requirement for new energy to enter the system. Photosynthesizing organisms use a series of oxidation-reduction reactions based on solar input to produce and store their own carbohydrates, which then become the energy source for other organisms. Ecosystems and Energy The food consumed by an organism will undergo a number of chemical reactions that are collectively referred to as metabolism. Materials in addition to water are transported across cell membranes.
These processes are facilitated by carrier proteins embedded within the membrane. The detailed transformation of nutrients is beyond the scope of this discussion. Descriptions of these processes may be found by searching for information on the Krebs (citric acid) Cycle. Students should understand that organisms take in nutrients, the energy of which becomes available through oxidation and reduction reactions.indd 4 8/15/08 4:21:01 PM Ecosystem Energy Flow: An Introduction to Energy and Laws of Thermodynamics Extremophiles should be briefly considered in this course.
These organisms live under severe conditions; some never receive sunlight or may be found clustered around underwater vents producing superheated boiling water. Their source of energy is through chemosynthesis, the process in which inorganic compounds such as nitrites, hydrogen sulfide, and hydrogen gas provide the necessary energy for these organisms to produce their own organic food. This information is sufficient to explain chemosynthesis without going into further detail. Photosynthesis 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) in their chloroplasts, which then reduce carbon dioxide and water to form a carbohydrate (glucose) only in the presence of sunlight and chlorophyll.
This process is actually a complex series of reactions where radiant energy is transformed into chemical energy. This series of reactions produces most of the oxygen in our atmosphere. 6CO 2 + 6H 2O —> C 6H 12O 6 + 6O 2 carbon water light glucose oxygen dioxide & chlorophyll Cellular Respiration In this process, carbon dioxide, water, and available energy are produced by the oxidation of glucose. This series of chemical reactions occurs in all living cells.
In aerobic organisms (those that can utilize oxygen). It is a process that requires oxygen and occurs at the cellular mitochondria; however, the first steps in the transformation of glucose take place in the cytoplasm rather than within the mitochondria and do not require oxygen. If the reaction never proceeds to the mitochondria, the organism has carried out anaerobic respiration, also known as fermentation. These first processes are 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) and NADPH (a carrier for electrons used in the synthesis of glucose). C 6H 12O 6 + 6O 2 —> 6CO 2 + 6H 2O glucose oxygen carbon water dioxide Trophic Levels A producer, or autotroph, is an organism that makes its own food by either photosynthesis or chemosynthesis. A consumer, or heterotroph, is an organism 5 08-1453.indd 5 8/15/08 4:21:01 PM Special Focus: Ecology that receives its energy from other organisms. Each step in the transfer of energy (autotroph to heterotroph and heterotroph to heterotroph) is known as a trophic level.
The laws of thermodynamics apply to the energy flow through an ecosystem; therefore, less energy is available to organisms at each higher trophic level. This decreased amount of available energy at each trophic level is due to the amount of energy required by an organism to carry out the daily functions of living. It is estimated that only 10 percent of the energy at each trophic level is available to organisms at the next higher level. Decomposers are often overlooked when considering trophic levels.
These organisms receive their nutrients and energy while breaking down and recycling organic materials.