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Biology - Unpacking Ecological Energy Flow
Learning Goal for Biology: Ecology
National Science Education Standard
THE INTERDEPENDENCE OF ORGANISMS
The atoms and molecules on the earth cycle among the living and nonliving components of the biosphere.
Energy flows through ecosystems in one direction, from photosynthetic organisms to herbivores to carnivores and decomposers.
Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.
Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms.
Human beings live within the world's ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected.
- NSES at
Michigan Ecology Standard Relating to the Interdependence of Living Systems and the Environment
STANDARD B3: "Students describe the processes of photosynthesis and cellular respiration and how energy is transferred through food webs. They recognize and analyze the consequences of the dependence of organisms on environmental resources and the interdependence of organisms in ecosystems" (Michigan Biology Content Standards p. 17).
Content, Identifying and Using Performances
B3.1 Photosynthesis and Respiration
Organisms acquire their energy directly or indirectly from sunlight. Plants capture the Sun’s energy and use it to convert carbon dioxide and water to sugar and oxygen through the process of photosynthesis. Through the process of cellular respiration, animals are able to release the energy stored in the molecules produced by plants and use it for cellular processes, producing carbon dioxide and water.
B3.1A Describe how organisms acquire energy directly or indirectly from sunlight.
B3.1B Illustrate and describe the energy conversions that occur during photosynthesis and respiration.
B3.1C Recognize the equations for photosynthesis and respiration and identify the reactants and products for both.
B3.1D Explain how living organisms gain and use mass through the processes of photosynthesis and respiration.
B3.1E Write the chemical equation for photosynthesis and cellular respiration and explain in words what they mean.
B3.1FSummarize the process of photosynthesis.
The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in an ecosystem, some energy is stored in newly made structures, but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.
B3.2A Identify how energy is stored in an ecosystem.
B3.2B Describe energy transfer through an ecosystem, accounting for energy lost to the environment as heat.
B3.2C Draw the flow of energy through an ecosystem. Predict changes in the food web when one or more organisms are removed.
B3.3 Element Recombination
As matter cycles and energy flows through different levels of organization of living systems—cells, organs, organisms, and communities—and between living systems and the physical environment, chemical elements are recombined in different ways. Each recombination results in storage and dissipation of energy into the environment as heat. Matter and energy are conserved in each change.
B3.3A Use a food web to identify and distinguish producers, consumers, and decomposers and explain the transfer of energy through trophic levels.
B3.3B Describe environmental processes (e.g., the carbon and nitrogen cycles) and their role in processing matter crucial for sustaining life.
B3.4 Changes in Ecosystems
Although the interrelationships and interdependence of organisms may generate biological communities in ecosystems that are stable for hundreds or thousands of years, ecosystems always change when climate changes or when one or more new species appear as a result of migration or local evolution. The impact of the human species has major consequences for other species.
B3.4A Describe ecosystem stability. Understand that if a disaster such as flood or fire occurs, the damaged ecosystem is likely to recover in stages of succession that eventually result in a system similar to the original one.
B3.4B Recognize and describe that a great diversity of species increases the chance that at least some living organisms will survive in the face of cataclysmic changes in the environment.
B3.4C Examine the negative impact of human activities.
B3.4x Human Impact
Humans can have tremendous impact on the environment. Sometimes their impact is beneficial, and sometimes it is detrimental.
B3.4d Describe the greenhouse effect and list possible causes.
B3.4e List the possible causes and consequences of global warming.
Populations of living things increase and decrease in size as they interact with other populations and with the environment. The rate of change is dependent upon relative birth and death rates.
B3.5A Graph changes in population growth, given a data table.
B3.5B Explain the influences that affect population growth.
B3.5C Predict the consequences of an invading organism on the survival of other organisms.
B3.5x Environmental Factors
The shape of population growth curves vary with the type of organism and environmental conditions, such as availability of nutrients and space. As the population increases and resources become more scarce, the population usually stabilizes at the carrying capacity of that environment.
B3.5d Describe different reproductive strategies employed by various organisms and explain their advantages and disadvantages.
B3.5e Recognize that and describe how the physical or chemical environment may influence the rate, extent, and nature of population dynamics within ecosystems.
B3.5f Graph an example of exponential growth. Then show the population leveling off at the carrying capacity of the environment.
B3.5g Diagram and describe the stages of the life cycle for a human disease-causing organism. (recommended)
Unpacking these statements:
Students need to understand that organisms do not exist in isolation. Biological organisms interact with each other and their environment in complex ways. Most of these interactions involve the exchange of energy and matter. It is also possible for organisms to provide shelter for each other. In addition, it is important for students to understand that energy from the sun is initially stored in glucose by plants through the process of photoysynthesis. The energy in glucose is used by organisms through the process of cellular respiration. Energy is transferred between organisms in food webs when one organism consumes or parasitizes another organism. It is important for students to understand how organisms depend on environmental resources, such as nitrogen, and how limitations on these resources affect organisms. Finally, it is important for students to understand how organisms depend on each other and how changes in the population of one organism affect other populations of organisms.
What do these statements mean about learning Ecology:
Students should be able to:
*Explain how energy from the sun is captured by plants and stored in sugar molecules. The energy in sugar molecules can be transferred to other long term storage molecules, such as sugar, fat, starch, and protein molecules.
*Draw a food chain, using arrows to indicate the flow of energy between organisms, and explain how energy is transferred from one organism to another. Specifically, be able to explain how when one organism eats or parasitizes another organism it acquires the other organism's sugar, fat, starch, and protein molecules, which store energy. It uses the energy stored in these molecules by the proccess of metabolism and cellular respiration.
*Given a food chain, identify where energy is lost to the environment as heat, and explain what accounts for the loss of energy. Specifically, explain how each organism in the food chain uses some of the energy it consumes in its own life processes, which is given off as heat, and that only 10% of the energy that an organism consumes is stored in it's body when it dies. As a result, only 10% of the energy in the food chain is transferred at each step in the food chain. Explain how the food chain is sustained, despite the loss of energy, by the continual input of energy from the sun.
*Given a food chain, explain the consequences to the food chain when one of the organisms is removed. They should be able to explain the consequences to the direct and indirect consumers. They should understand that the loss of an organism has far reaching consequences in a food chain.
*Given a food chain, explain the consequences to the food chain when an organism is added. They should be able to explain the consequences to the direct and indirect consumers. They should uncerstand that the addition of an organism has far reaching consequence in a food chain.
*Understand that organisms acquire energy directly or indirectly through from sunlight. They will understand that autotrophs use the sun’s energy to produce their own compounds, and that heterotrophs then must consume other organisms to produce their nutrients, and that this is an indirect way of obtaining energy from the sun.
*Understand that plants use light energy and convert it into chemical energy through the synthesis of carbohydrates. They will also understand that during cellular respiration that these carbohydrates are broken down, and this chemical energy is used to produce ATP.
*Recognize that during photosynthesis that six carbon dioxide molecules and six water molecules are used to create one molecule of glucose and six molecules of oxygen gas. They will be able to recognize that the carbon dioxide and water molecules are the reactants in photosynthesis, and that the glucose and oxygen gas molecules are the products of photosynthesis.
*Recognize that during cellular respiration one molecule of glucose and six oxygen gas molecules, 38 molecules of ADP, and 38 Phosphorus molecules are converted into six molecules of carbon dioxide, six molecules of water, and 38 molecules of ATP. They must be able to recognize that glucose, and oxygen molecules are the reactants for cellular respiration, and that carbon dioxide, water and ATP are the products.
*Explain how plants are able to take carbon dioxide in the air, and through the part of photosynthesis know as the Calvin Cycle, convert that carbon dioxide into carbohydrates, thus gaining mass through the process of photosynthesis. They must also understand that organisms then use this mass through the process of cellular respiration in order to make energy for cell function.
*Write out the chemical equations for photosynthesis and cellular respiration, being able to explain in words what each part means. They should be able to note which products result in the generation of energy, and which products result in the generation of mass.
*Summarize that photosynthesis takes place in two parts, light dependent and light independent reactions. They should know that in the light dependent reactions chlorophyll molecules use energy from the sun to transfer energy to electrons which are then passed from the chlorophyll to an electron transport chain, which are a series of proteins imbedded in the membrane of the chloroplast. They should also know that as the electron is passed down the electron transport chain the electron loses energy, which is used to make ATP molecules, and the electron is eventually added to an electron carrying molecule NADP+, which makes NADPH. Also, they should know that to replace this electron in the chlorophyll a water molecule is split, producing electrons for the chlorophyll, and releasing oxygen molecules into the environment. Students should understand that in the light-independent reactions of photosynthesis, also known as the Calvin Cycle, carbon dioxide, ATP, and NADPH are used to synthesize glucose. Lastly, students should understand that the Calvin Cycle is circular, and that it takes six rounds of the Calvin Cycle to produce one molecule of glucose.
*Identify and distinguish producers, consumers, and decomposers and explain the transfer of energy through trophic levels in food webs they have created. They will understand that energy is recombined and dissipated as heat as one trophic level is consumed by another. They will understand however, that energy and matter are conserved, and that the energy lost to the organisms in higher trophic levels is not lost to the environment, it is simply in another form.
*Describe environmental processes (e.g., the carbon, nitrogen, water and phosphorus cycles) and their role in processing matter crucial for sustaining life.
Describe ecosystem stability/fragility and understand that if a disaster such as flood or fire occurs, the damaged ecosystem is likely to recover in stages of succession that eventually result in a system similar to the original one. They will recognize that ecosystems are not 100% stable systems, but are subject to change through natural disasters and human influence.
*Recognize and describe that a great diversity of species increases the chance that at least some living organisms will survive in the face of cataclysmic changes in the environment. They will understand the positive aspects of biodiversity and be able to provide some examples where biodiversity is being lost, i.e. genetic modification in crops and invasive species issues.
*Understand how human activities are negatively impacting ecosystems, such as air, water, and land pollution, and habitat degradation. Also, they will understand human activities providing positive impacts on ecosystems, such as making habitat corridors, and species protection programs.
*Describe the greenhouse effect and list possible causes as well as consequences of global warming. They will be able to articulate how global warming can be addressed/curbed.
*Understand how they as individuals and as community members can be a positive, responsible influence on ecosystems and the environment.
*Describe different reproductive strategies and explain the advantages and disadvantages of each. Students will be able to compare and contrast the different reproductive strategies as they relate to various organisms and their life cycles.
*Describe how the chemical and physical environment may influence rate, extent, and nature of population dynamics within ecosystems. This includes abiotic factors and biotic factors. Some abiotic factors are intensity of light, range of temperatures, amount of moisture, type of substratum, availability of inorganic substances, supply of gases, and pH. Biotic factors involve all living things that directly or indirectly affect environment including: presence of organisms, their composition, their interactions, their wastes, and their nutritional and symbiotic relationships.
*Graph exponential growth of a population and how the graph behaves as the carrying capacity of the environment is reached. They will be able to define carrying capacity as the maximum number of organisms of a population that can be supported by the environment and its resources. They will understand that exponential growth is density-dependent population growth and the growth rate DECREASES and levels off as the population approaches carrying capacity.
*Predict the consequences of an invading organism on the survival of other organisms. They will understand that communities are composed of populations that are able to survive under existing conditions. They will understand the idea of niche, being able to differentiater between fundamental and realized niche. Students will specifically understand the effect of an exotic species on the realized niche(s) of native species.
What do students need to know to learn Ecology?
Michigan Biology Content Standards provides a list of prerequisites for Standard B3:
L3.p1 Populations, Communities, and Ecosystems (prerequisite)
Organisms of one species form a population. Populations of different organisms interact and form communities. Living communities and the nonliving factors that interact with them form ecosystems. (prerequisite)
L3.p1A Provide examples of a population, community, and ecosystem. (prerequisite)
L3.p2 Relationships Among Organisms (prerequisite)
Two types of organisms may interact with one another in several ways; they may be in a producer/consumer, predator/prey, or parasite/host relationship. Or one organism may scavenge or decompose another. Relationships may be competitive or mutually beneficial. Some species have become so adapted to each other that neither could survive without the other. (prerequisite)
L3.p2A Describe common relationships among organisms and provide examples of producer/consumer, predator/prey, or parasite/host relationship. (prerequisite)
L3.p2B Describe common ecological relationships between and among species and their environments (competition, territory, carrying capacity, natural balance, population, dependence, survival, and other biotic and abiotic factors). (prerequisite)
L3.p2C Describe the role of decomposers in the transfer of energy in an ecosystem. (prerequisite)
L3.p2D Explain how two organisms can be mutually beneficial and how that can lead to interdependency. (prerequisite)
L3.p3 Factors Influencing Ecosystems (prerequisite)
The number of organisms and populations an ecosystem can support depends on the biotic resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. (prerequisite)
L3.p3A Identify the factors in an ecosystem that influence fluctuations in population size. (prerequisite)
L3.p3B Distinguish between the living (biotic) and nonliving (abiotic) components of an ecosystem. (prerequisite)
L3.p3C Explain how biotic and abiotic factors cycle in an ecosystem (water, carbon, oxygen, and nitrogen). (prerequisite)
L3.p3D Predict how changes in one population might affect other populations based upon their relationships in a food web. (prerequisite)
L3.p4 Human Impact on Ecosystems (prerequisite)
All organisms cause changes in their environments. Some of these changes are detrimental, whereas others are beneficial. (prerequisite)
L3.p4A Recognize that, and describe how, human beings are part of Earth’s ecosystems. Note that human activities can deliberately or inadvertently alter the equilibrium in ecosystems. (prerequisite)
(Michigan Biology Content Standards p. 17)
What preconceptions might students have?
Students might think:
Animals get their energy from the outside environment, and plants get their energy from the soil by using their roots.
Organsims at the top of the food chain eat all of the organisms below them in the food chain.
Students believe there is a starting and ending point in the food chain.
The top of the food chain has the most energy becuase it is the "top" of the food chain (i.e. energy accumulates up the food chain).
The numbers of organisms at the top of the food chain are higher because they eat the organims lower in the food chain.
There are more herbivores soley because people keep and breed them.
Decomposers release some energy that is cycled back to plants.
Diagrams of energy pyramids that indicate decreases in energy (without indicating that the energy is given off as heat) can reinforce students' misconception that energy is not conserved.
The number of producers is high to satisfy consumers.
Students believe energy can be recycled through an ecosystem many times.
Plants do not live in water.
Often students will only address the components of a food chain that they can see. This is often reinforced by teachers using those components that are observable in their particular local.
Plants are dependent on humans, not vice versa.
Carbon dioxide is a source of energy for plants.
Energy is not lost in trophic transfer.
Energy comes from fuel (like gasoline) which makes power. Students may not think of a plant or animal as a source of power/energy.
Students may only think of energy in association with humans. (i.e. Energy is like bouncing around.)
Students may get stuck in thinking about individual organisms that do not fit the food web pattern.
Students may not see the overall flow of energy in an ecosystem.
Students may visualize flow only in terms of water and not grasp the concept that it means something starts in one place and gradually moves to another (In our case, energy flows through the food web slowly).
Varying the population of an organism will only affect the others that are directly connected through a food chain.
Varying the population of an organism may not affect an ecosystem, because some organisms are not important.
Varying the population of an organism will affect all other organisms to the same degree.
Populations higher on a food web increase in number because they deplete those lower in the web.
Ecosystems are not an organized whole, but a collection of organisms.
Communities change little over time.
Decomposers release some energy that is cycled back to plants.
The number of producers is high to satisfy consumers.
An organism cannot change trophic levels.
Humans provide food for other organisms.
The climax community is usually the final stage, long-lasting, and self-perpetuating.
Succession involves separate stages leading ultimately to deterministic climax.
Species coexist in an ecological system because of their compatible needs and behaviors: they “get along.”
The needs and roles of a species are general and typical of species.
Green plants are only producers of carbohydrates in ecosystems.
Plants take in food from the outside environment, and/or plants get their food from the soil via roots.
Food webs are interpreted as simple food chains.
The relative sizes of prey and predator populations have no bearing on the size of each other.
In a food web, a change in one population will only affect another population if the two populations are directly related as predator and prey.
Food chains involve predator and prey, no producers.
Carnivores are big or ferocious. Herbivores are passive or smaller.
Carnivores have more energy or power than herbivores do.
Traits are developed by individuals in response to the needs of the individual.
Traits develop because they are part of a predetermined plan.
Traits are properties of populations.
Traits are passed on by the bigger, stronger organisms that replace the smaller, weaker ones.
Adaptation equals evolution.
All factors are limiting except the most abundant one.
The most limiting factor is the least abundant one.
Populations exist in states of either constant growth or decline depending upon their position in a food chain.
Some ecosystems are limitless resources and provide an opportunity for limitless growth of a population.
Density-dependent factors are biotic, and density-idependent factors are abiotic.
Populations increase until limits are reached, then they crash and go extinct.
Plants are weak and cannot defend themselves.
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