Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties.
All biological systems are composed of parts that interact with each other. These interactions result in characteristics not found in the individual parts alone. In other words, “the whole is greater than the sum of its parts.” All biological systems from the molecular level to the ecosystem level exhibit properties of biocomplexity and diversity. Together, these two properties provide robustness to biological systems, enabling greater resiliency and flexibility to tolerate and respond to changes in the environment. Biological systems with greater complexity and diversity often exhibit an increased capacity to respond to changes in the environment. At the molecular level, the subcomponents of a biological polymer
determine the properties of that polymer. At the cellular level, organelles interact with each other as part of a coordinated system that keeps
the cell alive, growing and reproducing. The repertory of subcellular organelles and biochemical pathways reflects cell structure and differentiation. Additionally, interactions between external stimuli and gene expression result in specialization and divergence of cells, organs and tissues. Interactions and coordination between organs and organ systems determine essential biological activities for the organism as a whole. External and internal environmental factors can trigger responses in individual organs that, in turn, affect the entire organism. At the population level, as environmental conditions change, community structure changes both physically and biologically. The study of ecosystems seeks to understand the manner in which species are distributed in nature and how they are influenced by their abiotic and biotic interactions, e.g., species interactions. Interactions between living
organisms and their environments result in the movement of matter and energy. Interactions, including competition and cooperation, play important roles
in the activities of biological systems. Interactions between molecules affect their structure and function. Competition between cells may occur
under conditions of resource limitation. Cooperation between cells can improve efficiency and convert sharing of resources into a net gain in fitness for the organism. Coordination of organs and organ systems provides an organism with the ability to use matter and energy effectively. Variations in components within biological systems provide a greater flexibility to respond to changes in its environment. Variation in molecular units provides cells with a wider range of potential functions. A population is often measured in terms of genomic diversity and its ability to respond to change. Species with genetic variation and the resultant phenotypes can respond and adapt to changing environmental conditions. Enduring understanding 4.A: Interactions within biological systems lead to complex properties. All biological systems, from cells to ecosystems, are composed of parts that interact with each other. When this happens, the resulting interactions enable characteristics not found in the individual parts alone. In other words, “the whole is greater than the sum of its parts,” a phenomenon sometimes referred to as “emergent properties.” At the molecular level, the properties of a polymer are determined by its subcomponents and their interactions. For example, a DNA molecule is comprised of a series of nucleotides that can be linked together in various sequences; the resulting polymer carries hereditary material for the cell, including information that controls cellular activities. Other polymers important to life include carbohydrates, lipids and proteins. The interactions between the constituent parts of polymers, their order, their molecular orientation and their interactions with their environment define the structure and function of the polymer. At the cellular level, organelles interact with each other and their environment as part of a coordinated system that allows cells to live, grow and reproduce. For example, chloroplasts produce trioses through
the process of photosynthesis; however, once trioses are synthesized and exported from the chloroplast, they may be packaged by the Golgi body
and distributed to the edge of the cell where they serve as a building block for cellulose fibers comprising the cell wall. Similarly, several organelles
are involved in the manufacture and export of protein. The repertory of subcellular organelles determines cell structure and differentiation;
for instance, the components of plant leaf cells are different from the components of plant root cells, and the components of human liver cells are different from those in the retina. Thus, myriad interactions of different parts at the subcellular level determine the functioning of the entire cell, which would not happen with the activities of individual organelles alone. In development, interactions between regulated gene expression and external stimuli, such as temperature or nutrient levels or signal molecules, result in specialization of cells, organs and tissues. Differentiation of the germ layers during vertebrate gastrulation is an example of one such divergence. The progression of stem cells to terminal cells can also be explained by the interaction of stimuli and genes. Additionally, cells, organs and tissues may change due to changes in gene expression triggered by internal cues, including regulatory proteins and growth factors, which result in the structural and functional divergence of cells. Organisms exhibit complex properties due to interactions of their constituent parts, and interactions and coordination between organs and organ systems provide essential biological activities for the organism
as a whole. Examples include the vessels and hearts of animals and the roots and shoots of plants. Environmental factors such as temperature
can trigger responses in individual organs that, in turn, affect the entire organism. Interactions between populations within communities also lead to
complex properties. As environmental conditions change in time and space, the structure of the community changes both physically and biologically, resulting in a mosaic in the landscape (variety or patterns ) in a community. Communities are comprised of different populations of organisms that interact with each other in either negative or positive ways (e.g., competition, parasitism and mutualism); community ecology seeks to understand the manner in which groupings of species are distributed in nature, and how they are influenced by their abiotic environment and species interactions. The physical structure of a community is affected by abiotic factors, such as the depth and flow of water in a stream, and also by the spatial distribution of organisms, such as in the canopy of trees. The mix of species in terms of both the number of individuals and the diversity of species defines the structure of the community. Mathematical or computer models can be used to illustrate and investigate interactions of populations within a community and the effects of environmental impacts on a community. Community change resulting from disturbances sometimes follows a pattern (e.g., succession following a wildfire), and in other cases is random and unpredictable (e.g., founder effect). At the ecosystem level, interactions among living organisms and with their environment result in the movement of matter and energy. Ecosystems include producers, consumers, decomposers and a pool of organic matter,
plus the physiochemical environment that provides the living conditions for the biotic components. Matter, but not energy, can be recycled within
an ecosystem via biogeochemical cycles. Energy flows through the system and can be converted from one type to another, e.g., energy available
in sunlight is converted to chemical bond energy via photosynthesis. Understanding individual organisms in relation to the environment and
the diverse interactions that populations have with one another (e.g., food chains and webs) informs the development of ecosystem models; models
allow us to identify the impact of changes in biotic and abiotic factors. Human activities affect ecosystems on local, regional and global scales.
Essential knowledge 4.A.1: The subcomponents of biological molecules and their sequence determine the properties of that molecule (video).
a. Structure and function of polymers are derived from the way their monomers are assembled.
Evidence of student learning is a demonstrated understanding of each of the following:
1. In nucleic acids, biological information is encoded in sequences of nucleotide monomers. Each nucleotide has structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate and a nitrogen base (adenine, thymine, guanine, cytosine or uracil). DNA and RNA differ in function and differ
slightly in structure, and these structural differences account for the differing functions.
✘ The molecular structure of specific nucleotides is beyond the scope of the course and the AP Exam.
2. In proteins, the specific order of amino acids in a polypeptide (primary structure) interacts with the environment to determine the overall shape of the protein, which also involves secondary tertiary and quaternary structure and, thus, its function. The R group of an amino acid can be categorized by
chemical properties (hydrophobic, hydrophilic and ionic), and the interactions of these R groups determine structure and function of that region of the protein.
✘ The molecular structure of specific amino acids is beyond the scope of the course and the AP Exam.
3. In general, lipids are nonpolar; however, phospholipids exhibit structural properties, with polar regions that interact with other polar molecules such as water, and with nonpolar regions where differences in saturation determine the structure and function of lipids.
✘ The molecular structure of specific lipids is beyond the scope of the course and the AP Exam.
4. Carbohydrates are composed of sugar monomers whose structures and bonding with each other by dehydration synthesis determine the properties and functions of the molecules. Example include: cellulose versus starch.
✘ The molecular structure of specific carbohydrate polymers is beyond the scope of the course and the AP Exam.
b. Directionality influences structure and function of the polymer.Evidence of student learning is a demonstrated understanding of each of the following:
1. Nucleic acids have ends, defined by the 3' and 5' carbons of the sugar in the nucleotide, that determine the direction in which complementary nucleotides are added during DNA synthesis and the direction in which transcription occurs (from 5' to 3').
2. Proteins have an amino (NH2) end and a carboxyl (COOH) end, and consist of a linear sequence of amino acids connected by the formation of peptide bonds by dehydration synthesis between the amino and carboxyl groups of adjacent monomers.
3. The nature of the bonding between carbohydrate subunits determines their relative orientation in the carbohydrate, which then determines the secondary structure of the carbohydrate.
Learning Objectives:
LO4.1The student is able to explain the connection between the sequence and the subcomponents of a biological polymer and its
properties.
LO4.2The student is able to refine representations and models to explain how the subcomponents of a biological polymer and their sequence determine the properties of that polymer.
LO4.3The student is able to use models to predict and justify that changes in the subcomponents of a biological polymer affect the functionality of the molecule.
Essential knowledge 4.A.2: The structure and function of subcellular components, and their interactions, provide essential cellular processes (video)
a. Ribosomes are small, universal structures comprised of two interacting parts: ribosomal RNA and protein. In a sequential manner, these cellular components interact to become the site of protein synthesis where the translation of the genetic instructions yields specific polypeptides.
b. Endoplasmic reticulum (ER) occurs in two forms: smooth and rough.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Rough endoplasmic reticulum functions to compartmentalize the cell, serves as mechanical support, provides site-specific protein synthesis with membrane-bound ribosomes and plays a role in intracellular transport.
2. In most cases, smooth ER synthesizes lipids.
✘ Specific functions of smooth ER in specialized cells are beyond the scope of the course and the AP Exam.
c. The Golgi complex is a membrane-bound structure that consists of a series of flattened membrane sacs (cisternae).
Evidence of student learning is a demonstrated understanding of the following:
1. Functions of the Golgi include synthesis and packaging of materials (small molecules) for transport (in vesicles), and production of lysosomes.
✘ The role of this organelle in specific phospholipid synthesis and the packaging of enzymatic contents of lysosomes, peroxisomes and secretory vesicles are beyond the scope of the course and the AP Exam.
d. Mitochondria specialize in energy capture and transformation.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Mitochondria have a double membrane that allows compartmentalization within the mitochondria and is important to its function.
2. The outer membrane is smooth, but the inner membrane is highly convoluted, forming folds called cristae.
3. Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production.
e. Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes, which are important in intracellular digestion, the recycling of a cell’s organic materials and programmed cell death (apoptosis). Lysosomes carry out intracellular digestion in a variety of ways.
✘ Specific examples of how lysosomes carry out intracellular digestion are beyond the scope of the course and the AP Exam.
f. A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In plants, a
large vacuole serves many functions, from storage of pigments or poisonous substances to a role in cell growth. In addition, a large central vacuole allows for a large surface area to volume ratio.
g. Chloroplasts are specialized organelles found in algae and higher plants that capture energy through photosynthesis.
Evidence of student learning is a demonstrated understanding of each of the following:
1. The structure and function relationship in the chloroplast allows cells to capture the energy available in sunlight and convert it to chemical bond energy via photosynthesis.
2. Chloroplasts contain chlorophylls, which are responsible for the green color of a plant and are the key light-trapping molecules in photosynthesis. There are several types of chlorophyll, but the predominant form in plants is chlorophyll a.
✘ The molecular structure of chlorophyll a is beyond the scope of the course and the AP Exam.
3. Chloroplasts have a double outer membrane that creates a compartmentalized structure, which supports its function.
Within the chloroplasts are membrane-bound structures called thylakoids. Energy-capturing reactions housed in the thylakoids are organized in stacks, called “grana,” to produce ATP and NADPH2, which fuel carbon-fixing reactions in the Calvin-Benson cycle. Carbon fixation occurs in the stroma,
where molecules of CO2 are converted to carbohydrates.
Learning Objectives:
LO4.4The student is able to make a prediction about the interactions of subcellular organelles.
LO4.5The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures
provide essential functions.
LO4.6The student is able to use representations and models to analyze situations qualitatively to describe how interactions of subcellular structures, which possess specialized functions, provide essential functions.
Essential knowledge 4.A.3: Interactions between external stimuli and regulated gene expression result in specialization of cells, tissues and organs (video).
a. Differentiation in development is due to external and internal cuesthat trigger gene regulation by proteins that bind to DNA.
b. Structural and functional divergence of cells in development is due to expression of genes specific to a particular tissue or organ type.
c. Environmental stimuli can affect gene expression in a mature cell.
Learning Objective:
LO4.7The student is able to refine representations to illustrate how interactions between external stimuli and gene expression
result in specialization of cells, tissues and organs.
Essential knowledge 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts (video).
a. Interactions and coordination between organs provide essential biological activities.
illustrative examples:
• Stomach and small intestines
• Kidney and bladder
• Root, stem and leaf
b. Interactions and coordination between systems provide essential biological activities.
illustrative examples:
• Respiratory and circulatory
• Nervous and muscular
• Plant vascular and leaf Learning Objectives:
LO4.8The student is able to evaluate scientific questions concerning organisms that exhibit complex properties due to the interaction of their constituent parts.
LO4.9The student is able to predict the effects of a change in a component(s) of a biological system on the functionality of an organism(s).
LO4.10The student is able to refine representations and models to illustrate biocomplexity due to interactions of the constituent parts.
Essential knowledge 4.A.5: Communities are composed of populations of organisms that interact in complex ways (video).
a. The structure of a community is measured and described in terms of species composition and species diversity.
b. Mathematical or computer models are used to illustrate and investigate population interactions within and environmental impacts on a community.
illustrative examples:
• Predator/prey relationships spreadsheet model
• Symbiotic relationship
• Graphical representation of field data
• Introduction of species
• Global climate change models
c. Mathematical models and graphical representations are used to illustrate population growth patterns and interactions.
Evidence of student learning is a demonstrated understanding of each of the following
1. Reproduction without constraints results in the exponential growth of a population.
2. A population can produce a density of individuals that exceeds the system’s resource availability.
3. As limits to growth due to density-dependent and densityindependent factors are imposed, a logistic growth model generally ensues.
4. Demographics data with respect to age distributions and fecundity can be used to study human populations.
Learning Objectives:
LO4.11The student is able to justify the selection of the kind of data needed to answer scientific questions about the interaction of
populations within communities.
LO4.12The student is able to apply mathematical routines to quantities that describe communities composed of populations of organisms that interact in complex ways.
LO4.13The student is able to predict the effects of a change in the community’s populations on the community.
Essential knowledge 4.A.6: Interactions among living systems and with their environment result in the movement of matter and energy.
a. Energy flows, but matter is recycled.
b. Changes in regional and global climates and in atmospheric composition influence patterns of primary productivity.
c. Organisms within food webs and food chains interact.
d. Food webs and food chains are dependent on primary productivity.
e. Models allow the prediction of the impact of change in biotic and abiotic factors.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Competition for resources and other factors limits growth and can be described by the logistic model.
2. Competition for resources, territoriality, health, predation, accumulation of wastes and other factors contribute to density dependent population regulation.
f. Human activities impact ecosystems on local, regional and global scales.
Evidence of student learning is a demonstrated understanding of each of the following:
1. As human populations have increased in numbers, their impact on habitats for other species have been magnified.
2. In turn, this has often reduced the population size of the affected species and resulted in habitat destruction and, in some cases, the extinction of species.
g. Many adaptations of organisms are related to obtaining and using energy and matter in a particular environment.
Learning Objectives:
LO4.14The student is able to apply mathematical routines to quantities that describe interactions among living systems and their environment, which result in the movement of matter and energy.
LO4.15The student is able to use visual representations to analyze situations or solve problems qualitatively to illustrate how interactions among living systems and with their environment result in the movement of matter and energy.
LO4.16The student is able to predict the effects of a change of matter or energy availability on communities.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.
Summary: Competition and cooperation play important roles in the activities of biological systems at all levels of organization. Living systems require
a myriad of chemical reactions on a constant basis, and each of these chemical reactions relies on the cooperation between a particular enzyme
and specific substrates, coenzymes and cofactors. Chemical inhibitors maycompete for the active sites of enzymes that, in turn, affect the ability of
the enzyme to catalyze its chemical reactions. Thus, interactions between molecules affect their structure and function. Other examples of this
phenomenon include receptor-ligand interactions and changes in protein structure due to amino acid sequence. Similar cells may compete with each other when resources are limited; for example, organisms produce many more spores or seeds than will germinate. Competition for resources also determines which organisms are successful and produce offspring. In the vertebrate immune system, competition via antigen-binding sites determines which B-cell lineages are stimulated to reproduce. The cooperation of parts extends to the organism that depends on the coordination of organs and organ systems, such as between the digestive and excretory systems of an animal or the roots and shoots of a plant. Cooperation within organisms increases efficiency in the use of matter and energy. For example, without the coordination and cooperation of its shoot and roots, a plant would be unable to survive if its root system was too small to absorb water to replace the water lost through transpiration by the shoot. Similarly, exchange of oxygen and carbon dioxide in an animal depends on the functioning of the respiratory and circulatory systems. Furthermore, population interactions influence patterns of species distribution and abundance, and global distribution of ecosystems changes substantially over time.
Essential knowledge 4.B.1: Interactions between molecules affect their structure and function (video).
a. Change in the structure of a molecular system may result in a change of the function of the system.
b. The shape of enzymes, active sites and interaction with specific molecules are essential for basic functioning of the enzyme.
Evidence of student learning is a demonstrated understanding of each of the following:
1. For an enzyme-mediated chemical reaction to occur, the substrate must be complementary to the surface properties (shape and
charge) of the active site. In other words, the substrate must fit into the enzyme’s active site.
2. Cofactors and coenzymes affect enzyme function; this interaction relates to a structural change that alters the activity
rate of the enzyme. The enzyme may only become active when all the appropriate cofactors or coenzymes are present and bind to the appropriate sites on the enzyme.
✘ No specific cofactors or coenzymes are within the scope of the course and the AP Exam. c. Other molecules and the environment in which the enzyme
acts can enhance or inhibit enzyme activity. Molecules can bind reversibly or irreversibly to the active or allosteric sites, changing the activity of the enzyme.
d. The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/or presence of a competitive inhibitor.
Learning Objective:
LO4.17The student is able to analyze data to identify how molecular interactions affect structure and function. [See SP5.1]
Essential knowledge 4.B.2: Cooperative interactions within organisms promote efficiency in the use of energy and matter. (video)
a. Organisms have areas or compartments that perform a subset of functions related to energy and matter, and these parts contribute to the whole.
Evidence of student learning is a demonstrated understanding of each of the following:
1. At the cellular level, the plasma membrane, cytoplasm and, for eukaryotes, the organelles contribute to the overall specialization and functioning of the cell.
2. Within multicellular organisms, specialization of organs contributes to the overall functioning of the organism.
illustrative examples:
• Exchange of gases
• Circulation of fluids
• Digestion of food
• Excretion of wastes
3. Interactions among cells of a population of unicellular organisms can be similar to those of multicellular organisms, and these interactions lead to increased efficiency and utilization of energy and matter.To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Bacterial community in the rumen of animals
• Bacterial community in and around deep sea vents
Learning Objective:
LO4.18The student is able to use representations and models to analyze how cooperative interactions within organisms promote
efficiency in the use of energy and matter.
Essential knowledge 4.B.3: Interactions between and within populations influence patterns of species distribution and abundance (video).
a. Interactions between populations affect the distributions and abundance of populations.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Competition, parasitism, predation, mutualism and commensalism can affect population dynamics.
2. Relationships among interacting populations can be characterized by positive and negative effects, and can be modeled mathematically (predator/prey, epidemiological models, invasive species).
3. Many complex symbiotic relationships exist in an ecosystem, and feedback control systems play a role in the functioning of these ecosystems.
✘ Specific symbiotic interactions are beyond the scope of the course and the AP Exam.
b. A population of organisms has properties that are different from those of the individuals that make up the population. The cooperation and competition between individuals contributes to these different properties.
c. Species-specific and environmental catastrophes, geological events, the sudden influx/depletion of abiotic resources or increased human activities affect species distribution and abundance.
illustrative examples:
• Loss of keystone species
• Kudzu
• Dutch elm disease
Learning Objective:
LO4.19The student is able to use data analysis to refine observations and measurements regarding the effect of population interactions on patterns of species distribution and abundance.
Essential knowledge 4.B.4: Distribution of local and global ecosystems changes over time (video).
a. Human impact accelerates change at local and global levels.
illustrative examples:
• Logging, slash and burn agriculture, urbanization, monocropping, infrastructure development (dams, transmission lines, roads), and global climate change threaten ecosystems and life on Earth.
• An introduced species can exploit a new niche free of predators or competitors, thus exploiting new resources.
• Introduction of new diseases can devastate native species.
Illustrative examples:
• Dutch elm disease
• Potato blight
• Small pox [historic example for Native Americans]
b. Geological and meteorological events impact ecosystem distribution.
Evidence of student learning is a demonstrated understanding of the following:
1. Biogeographical studies illustrate these changes.
illustrative examples:
• El Niño
• Continental drift
• Meteor impact on dinosaurs
Learning Objectives:
LO4.20The student is able to explain how the distribution of ecosystems changes over time by identifying large-scale events that have resulted in these changes in the past.
LO4.21The student is able to predict consequences of human actions on both local and global ecosystems.
Enduring understanding 4.C: Naturally occurring diversity among and between components within biological systems affects interactions with the environment.
Summary: A biological system that possesses many different components often has greater flexibility to respond to changes in its environment. This
phenomenon is sometimes referred to as “robustness.” Variation in molecular units provides cells with a wider range of functions; cells with
multiple copies of genes or heterozygous genes possess a wider range of functions compared to cells with less genetic diversity, while cells with myriad
enzymes can catalyze myriad chemical reactions.Environmental factors influence the phenotypic expression of an organism’s genotype. In humans, weight and height are examples of complex traits that can be influenced by environmental conditions. However, even simple single gene traits can be influenced by the environment; for example, flower color in some species of plants is dependent upon the pH of the environment. Some organisms possess the ability to respond flexibly to environmental signals to yield phenotypes that allow them to adapt to changes in the environment in which they live. Environmental factors such as temperature or density can affect sex determination in some animals, while parthenogenesis can be triggered by reproductive isolation. Plant seed dormancy can increase the survival of a species, and some viruses possess both lysogenic and lytic life cycles.The level of variation in a population affects its dynamics. The ability of a population to respond to a changing environment (fitness) is often measured in terms of genomic diversity. Species with little genetic diversity, such as a population of plants that reproduces asexually or a very small population exhibiting a genetic bottleneck effect, are at risk with regard to long-term success and survival. Diversity of species within an ecosystem may influence the stability of the ecosystem. Ecosystems with little species diversity are often less resilient to changes in the environment. Keystone species, predators, and
essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. For example, the removal of sea otters or mollusks can drastically affect a marine ecosystem, and the introduction of an exotic plant or animal species can likewise affect the stability of a terrestrial ecosystem.
Essential knowledge 4.C.1: Variation in molecular units provides cells with a wider range of functions (video).
a. Variations within molecular classes provide cells and organisms with a wider range of functions. To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Different types of phospholipids in cell membranes
• Different types of hemoglobin
• MHC proteins
• Chlorophylls
• Molecular diversity of antibodies in response to an antigen
b. Multiple copies of alleles or genes (gene duplication) may provide new phenotypes.
Evidence of student learning is a demonstrated understanding of each of the following:
1. A heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with two different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.
2. Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function.
illustrative example such as:
• The antifreeze gene in fish
Learning Objective:
LO4.22The student is able to construct explanations based on evidence of how variation in molecular units provides cells with a wider range of functions.
Essential knowledge 4.C.2: Environmental factors influence the expression of the genotype in an organism (video).
a. Environmental factors influence many traits both directly and indirectly.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Height and weight in humans
• Flower color based on soil pH
• Seasonal fur color in arctic animals
• Sex determination in reptiles
• Density of plant hairs as a function of herbivory
• Effect of adding lactose to a Lac + bacterial culture
• Effect of increased UV on melanin production in animals
• Presence of the opposite mating type on pheromones production in yeast and other fungi
b. An organism’s adaptation to the local environment reflects a flexible response of its genome.
illustrative examples:
• Darker fur in cooler regions of the body in certain mammal species
• Alterations in timing of flowering due to climate changes
Learning Objectives:
LO4.23The student is able to construct explanations of the influence of environmental factors on the phenotype of an organism.
LO4.24The student is able to predict the effects of a change in an environmental factor on the genotypic expression of the phenotype.
Essential knowledge 4.C.3: The level of variation in a population affects population dynamics (video).
a. Population ability to respond to changes in the environment is affected by genetic diversity. Species and populations with little genetic diversity are at risk for extinction.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• California condors
• Black-footed ferrets
• Prairie chickens
• Potato blight causing the potato famine
• Corn rust affects on agricultural crops
• Tasmanian devils and infectious cancer
b. Genetic diversity allows individuals in a population to respond differently to the same changes in environmental conditions.
illustrative examples:
• Not all animals in a population stampede.
• Not all individuals in a population in a disease outbreak are equally affected; some may not show symptoms, some may have mild symptoms, or some may be naturally immune and resistant to the disease.
c. Allelic variation within a population can be modeled by the HardyWeinberg equation(s).
Learning Objectives:
LO4.25The student is able to use evidence to justify a claim that a variety of phenotypic responses to a single environmental factor can result from different genotypes within the population.
LO4.26The student is able to use theories and models to make scientific claims and/or predictions about the effects of variation
within populations on survival and fitness.
Essential knowledge 4.C.4: The diversity of species within an ecosystem may influence the stability of the ecosystem (video).
a. Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to
changes in the environment. [See also 1.C.1]
b. Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. The effects
of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem, and when they are removed from the ecosystem, the ecosystem often collapses.
Learning Objective:
LO4.27The student is able to make scientific claims and predictions about how species diversity within an ecosystem influences ecosystem stability.
determine the properties of that polymer. At the cellular level, organelles interact with each other as part of a coordinated system that keeps
the cell alive, growing and reproducing. The repertory of subcellular organelles and biochemical pathways reflects cell structure and differentiation. Additionally, interactions between external stimuli and gene expression result in specialization and divergence of cells, organs and tissues. Interactions and coordination between organs and organ systems determine essential biological activities for the organism as a whole. External and internal environmental factors can trigger responses in individual organs that, in turn, affect the entire organism. At the population level, as environmental conditions change, community structure changes both physically and biologically. The study of ecosystems seeks to understand the manner in which species are distributed in nature and how they are influenced by their abiotic and biotic interactions, e.g., species interactions. Interactions between living
organisms and their environments result in the movement of matter and energy. Interactions, including competition and cooperation, play important roles
in the activities of biological systems. Interactions between molecules affect their structure and function. Competition between cells may occur
under conditions of resource limitation. Cooperation between cells can improve efficiency and convert sharing of resources into a net gain in fitness for the organism. Coordination of organs and organ systems provides an organism with the ability to use matter and energy effectively. Variations in components within biological systems provide a greater flexibility to respond to changes in its environment. Variation in molecular units provides cells with a wider range of potential functions. A population is often measured in terms of genomic diversity and its ability to respond to change. Species with genetic variation and the resultant phenotypes can respond and adapt to changing environmental conditions. Enduring understanding 4.A: Interactions within biological systems lead to complex properties. All biological systems, from cells to ecosystems, are composed of parts that interact with each other. When this happens, the resulting interactions enable characteristics not found in the individual parts alone. In other words, “the whole is greater than the sum of its parts,” a phenomenon sometimes referred to as “emergent properties.” At the molecular level, the properties of a polymer are determined by its subcomponents and their interactions. For example, a DNA molecule is comprised of a series of nucleotides that can be linked together in various sequences; the resulting polymer carries hereditary material for the cell, including information that controls cellular activities. Other polymers important to life include carbohydrates, lipids and proteins. The interactions between the constituent parts of polymers, their order, their molecular orientation and their interactions with their environment define the structure and function of the polymer. At the cellular level, organelles interact with each other and their environment as part of a coordinated system that allows cells to live, grow and reproduce. For example, chloroplasts produce trioses through
the process of photosynthesis; however, once trioses are synthesized and exported from the chloroplast, they may be packaged by the Golgi body
and distributed to the edge of the cell where they serve as a building block for cellulose fibers comprising the cell wall. Similarly, several organelles
are involved in the manufacture and export of protein. The repertory of subcellular organelles determines cell structure and differentiation;
for instance, the components of plant leaf cells are different from the components of plant root cells, and the components of human liver cells are different from those in the retina. Thus, myriad interactions of different parts at the subcellular level determine the functioning of the entire cell, which would not happen with the activities of individual organelles alone. In development, interactions between regulated gene expression and external stimuli, such as temperature or nutrient levels or signal molecules, result in specialization of cells, organs and tissues. Differentiation of the germ layers during vertebrate gastrulation is an example of one such divergence. The progression of stem cells to terminal cells can also be explained by the interaction of stimuli and genes. Additionally, cells, organs and tissues may change due to changes in gene expression triggered by internal cues, including regulatory proteins and growth factors, which result in the structural and functional divergence of cells. Organisms exhibit complex properties due to interactions of their constituent parts, and interactions and coordination between organs and organ systems provide essential biological activities for the organism
as a whole. Examples include the vessels and hearts of animals and the roots and shoots of plants. Environmental factors such as temperature
can trigger responses in individual organs that, in turn, affect the entire organism. Interactions between populations within communities also lead to
complex properties. As environmental conditions change in time and space, the structure of the community changes both physically and biologically, resulting in a mosaic in the landscape (variety or patterns ) in a community. Communities are comprised of different populations of organisms that interact with each other in either negative or positive ways (e.g., competition, parasitism and mutualism); community ecology seeks to understand the manner in which groupings of species are distributed in nature, and how they are influenced by their abiotic environment and species interactions. The physical structure of a community is affected by abiotic factors, such as the depth and flow of water in a stream, and also by the spatial distribution of organisms, such as in the canopy of trees. The mix of species in terms of both the number of individuals and the diversity of species defines the structure of the community. Mathematical or computer models can be used to illustrate and investigate interactions of populations within a community and the effects of environmental impacts on a community. Community change resulting from disturbances sometimes follows a pattern (e.g., succession following a wildfire), and in other cases is random and unpredictable (e.g., founder effect). At the ecosystem level, interactions among living organisms and with their environment result in the movement of matter and energy. Ecosystems include producers, consumers, decomposers and a pool of organic matter,
plus the physiochemical environment that provides the living conditions for the biotic components. Matter, but not energy, can be recycled within
an ecosystem via biogeochemical cycles. Energy flows through the system and can be converted from one type to another, e.g., energy available
in sunlight is converted to chemical bond energy via photosynthesis. Understanding individual organisms in relation to the environment and
the diverse interactions that populations have with one another (e.g., food chains and webs) informs the development of ecosystem models; models
allow us to identify the impact of changes in biotic and abiotic factors. Human activities affect ecosystems on local, regional and global scales.
Essential knowledge 4.A.1: The subcomponents of biological molecules and their sequence determine the properties of that molecule (video).
a. Structure and function of polymers are derived from the way their monomers are assembled.
Evidence of student learning is a demonstrated understanding of each of the following:
1. In nucleic acids, biological information is encoded in sequences of nucleotide monomers. Each nucleotide has structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate and a nitrogen base (adenine, thymine, guanine, cytosine or uracil). DNA and RNA differ in function and differ
slightly in structure, and these structural differences account for the differing functions.
✘ The molecular structure of specific nucleotides is beyond the scope of the course and the AP Exam.
2. In proteins, the specific order of amino acids in a polypeptide (primary structure) interacts with the environment to determine the overall shape of the protein, which also involves secondary tertiary and quaternary structure and, thus, its function. The R group of an amino acid can be categorized by
chemical properties (hydrophobic, hydrophilic and ionic), and the interactions of these R groups determine structure and function of that region of the protein.
✘ The molecular structure of specific amino acids is beyond the scope of the course and the AP Exam.
3. In general, lipids are nonpolar; however, phospholipids exhibit structural properties, with polar regions that interact with other polar molecules such as water, and with nonpolar regions where differences in saturation determine the structure and function of lipids.
✘ The molecular structure of specific lipids is beyond the scope of the course and the AP Exam.
4. Carbohydrates are composed of sugar monomers whose structures and bonding with each other by dehydration synthesis determine the properties and functions of the molecules. Example include: cellulose versus starch.
✘ The molecular structure of specific carbohydrate polymers is beyond the scope of the course and the AP Exam.
b. Directionality influences structure and function of the polymer.Evidence of student learning is a demonstrated understanding of each of the following:
1. Nucleic acids have ends, defined by the 3' and 5' carbons of the sugar in the nucleotide, that determine the direction in which complementary nucleotides are added during DNA synthesis and the direction in which transcription occurs (from 5' to 3').
2. Proteins have an amino (NH2) end and a carboxyl (COOH) end, and consist of a linear sequence of amino acids connected by the formation of peptide bonds by dehydration synthesis between the amino and carboxyl groups of adjacent monomers.
3. The nature of the bonding between carbohydrate subunits determines their relative orientation in the carbohydrate, which then determines the secondary structure of the carbohydrate.
Learning Objectives:
LO4.1The student is able to explain the connection between the sequence and the subcomponents of a biological polymer and its
properties.
LO4.2The student is able to refine representations and models to explain how the subcomponents of a biological polymer and their sequence determine the properties of that polymer.
LO4.3The student is able to use models to predict and justify that changes in the subcomponents of a biological polymer affect the functionality of the molecule.
Essential knowledge 4.A.2: The structure and function of subcellular components, and their interactions, provide essential cellular processes (video)
a. Ribosomes are small, universal structures comprised of two interacting parts: ribosomal RNA and protein. In a sequential manner, these cellular components interact to become the site of protein synthesis where the translation of the genetic instructions yields specific polypeptides.
b. Endoplasmic reticulum (ER) occurs in two forms: smooth and rough.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Rough endoplasmic reticulum functions to compartmentalize the cell, serves as mechanical support, provides site-specific protein synthesis with membrane-bound ribosomes and plays a role in intracellular transport.
2. In most cases, smooth ER synthesizes lipids.
✘ Specific functions of smooth ER in specialized cells are beyond the scope of the course and the AP Exam.
c. The Golgi complex is a membrane-bound structure that consists of a series of flattened membrane sacs (cisternae).
Evidence of student learning is a demonstrated understanding of the following:
1. Functions of the Golgi include synthesis and packaging of materials (small molecules) for transport (in vesicles), and production of lysosomes.
✘ The role of this organelle in specific phospholipid synthesis and the packaging of enzymatic contents of lysosomes, peroxisomes and secretory vesicles are beyond the scope of the course and the AP Exam.
d. Mitochondria specialize in energy capture and transformation.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Mitochondria have a double membrane that allows compartmentalization within the mitochondria and is important to its function.
2. The outer membrane is smooth, but the inner membrane is highly convoluted, forming folds called cristae.
3. Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production.
e. Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes, which are important in intracellular digestion, the recycling of a cell’s organic materials and programmed cell death (apoptosis). Lysosomes carry out intracellular digestion in a variety of ways.
✘ Specific examples of how lysosomes carry out intracellular digestion are beyond the scope of the course and the AP Exam.
f. A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In plants, a
large vacuole serves many functions, from storage of pigments or poisonous substances to a role in cell growth. In addition, a large central vacuole allows for a large surface area to volume ratio.
g. Chloroplasts are specialized organelles found in algae and higher plants that capture energy through photosynthesis.
Evidence of student learning is a demonstrated understanding of each of the following:
1. The structure and function relationship in the chloroplast allows cells to capture the energy available in sunlight and convert it to chemical bond energy via photosynthesis.
2. Chloroplasts contain chlorophylls, which are responsible for the green color of a plant and are the key light-trapping molecules in photosynthesis. There are several types of chlorophyll, but the predominant form in plants is chlorophyll a.
✘ The molecular structure of chlorophyll a is beyond the scope of the course and the AP Exam.
3. Chloroplasts have a double outer membrane that creates a compartmentalized structure, which supports its function.
Within the chloroplasts are membrane-bound structures called thylakoids. Energy-capturing reactions housed in the thylakoids are organized in stacks, called “grana,” to produce ATP and NADPH2, which fuel carbon-fixing reactions in the Calvin-Benson cycle. Carbon fixation occurs in the stroma,
where molecules of CO2 are converted to carbohydrates.
Learning Objectives:
LO4.4The student is able to make a prediction about the interactions of subcellular organelles.
LO4.5The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures
provide essential functions.
LO4.6The student is able to use representations and models to analyze situations qualitatively to describe how interactions of subcellular structures, which possess specialized functions, provide essential functions.
Essential knowledge 4.A.3: Interactions between external stimuli and regulated gene expression result in specialization of cells, tissues and organs (video).
a. Differentiation in development is due to external and internal cuesthat trigger gene regulation by proteins that bind to DNA.
b. Structural and functional divergence of cells in development is due to expression of genes specific to a particular tissue or organ type.
c. Environmental stimuli can affect gene expression in a mature cell.
Learning Objective:
LO4.7The student is able to refine representations to illustrate how interactions between external stimuli and gene expression
result in specialization of cells, tissues and organs.
Essential knowledge 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts (video).
a. Interactions and coordination between organs provide essential biological activities.
illustrative examples:
• Stomach and small intestines
• Kidney and bladder
• Root, stem and leaf
b. Interactions and coordination between systems provide essential biological activities.
illustrative examples:
• Respiratory and circulatory
• Nervous and muscular
• Plant vascular and leaf Learning Objectives:
LO4.8The student is able to evaluate scientific questions concerning organisms that exhibit complex properties due to the interaction of their constituent parts.
LO4.9The student is able to predict the effects of a change in a component(s) of a biological system on the functionality of an organism(s).
LO4.10The student is able to refine representations and models to illustrate biocomplexity due to interactions of the constituent parts.
Essential knowledge 4.A.5: Communities are composed of populations of organisms that interact in complex ways (video).
a. The structure of a community is measured and described in terms of species composition and species diversity.
b. Mathematical or computer models are used to illustrate and investigate population interactions within and environmental impacts on a community.
illustrative examples:
• Predator/prey relationships spreadsheet model
• Symbiotic relationship
• Graphical representation of field data
• Introduction of species
• Global climate change models
c. Mathematical models and graphical representations are used to illustrate population growth patterns and interactions.
Evidence of student learning is a demonstrated understanding of each of the following
1. Reproduction without constraints results in the exponential growth of a population.
2. A population can produce a density of individuals that exceeds the system’s resource availability.
3. As limits to growth due to density-dependent and densityindependent factors are imposed, a logistic growth model generally ensues.
4. Demographics data with respect to age distributions and fecundity can be used to study human populations.
Learning Objectives:
LO4.11The student is able to justify the selection of the kind of data needed to answer scientific questions about the interaction of
populations within communities.
LO4.12The student is able to apply mathematical routines to quantities that describe communities composed of populations of organisms that interact in complex ways.
LO4.13The student is able to predict the effects of a change in the community’s populations on the community.
Essential knowledge 4.A.6: Interactions among living systems and with their environment result in the movement of matter and energy.
a. Energy flows, but matter is recycled.
b. Changes in regional and global climates and in atmospheric composition influence patterns of primary productivity.
c. Organisms within food webs and food chains interact.
d. Food webs and food chains are dependent on primary productivity.
e. Models allow the prediction of the impact of change in biotic and abiotic factors.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Competition for resources and other factors limits growth and can be described by the logistic model.
2. Competition for resources, territoriality, health, predation, accumulation of wastes and other factors contribute to density dependent population regulation.
f. Human activities impact ecosystems on local, regional and global scales.
Evidence of student learning is a demonstrated understanding of each of the following:
1. As human populations have increased in numbers, their impact on habitats for other species have been magnified.
2. In turn, this has often reduced the population size of the affected species and resulted in habitat destruction and, in some cases, the extinction of species.
g. Many adaptations of organisms are related to obtaining and using energy and matter in a particular environment.
Learning Objectives:
LO4.14The student is able to apply mathematical routines to quantities that describe interactions among living systems and their environment, which result in the movement of matter and energy.
LO4.15The student is able to use visual representations to analyze situations or solve problems qualitatively to illustrate how interactions among living systems and with their environment result in the movement of matter and energy.
LO4.16The student is able to predict the effects of a change of matter or energy availability on communities.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.
Summary: Competition and cooperation play important roles in the activities of biological systems at all levels of organization. Living systems require
a myriad of chemical reactions on a constant basis, and each of these chemical reactions relies on the cooperation between a particular enzyme
and specific substrates, coenzymes and cofactors. Chemical inhibitors maycompete for the active sites of enzymes that, in turn, affect the ability of
the enzyme to catalyze its chemical reactions. Thus, interactions between molecules affect their structure and function. Other examples of this
phenomenon include receptor-ligand interactions and changes in protein structure due to amino acid sequence. Similar cells may compete with each other when resources are limited; for example, organisms produce many more spores or seeds than will germinate. Competition for resources also determines which organisms are successful and produce offspring. In the vertebrate immune system, competition via antigen-binding sites determines which B-cell lineages are stimulated to reproduce. The cooperation of parts extends to the organism that depends on the coordination of organs and organ systems, such as between the digestive and excretory systems of an animal or the roots and shoots of a plant. Cooperation within organisms increases efficiency in the use of matter and energy. For example, without the coordination and cooperation of its shoot and roots, a plant would be unable to survive if its root system was too small to absorb water to replace the water lost through transpiration by the shoot. Similarly, exchange of oxygen and carbon dioxide in an animal depends on the functioning of the respiratory and circulatory systems. Furthermore, population interactions influence patterns of species distribution and abundance, and global distribution of ecosystems changes substantially over time.
Essential knowledge 4.B.1: Interactions between molecules affect their structure and function (video).
a. Change in the structure of a molecular system may result in a change of the function of the system.
b. The shape of enzymes, active sites and interaction with specific molecules are essential for basic functioning of the enzyme.
Evidence of student learning is a demonstrated understanding of each of the following:
1. For an enzyme-mediated chemical reaction to occur, the substrate must be complementary to the surface properties (shape and
charge) of the active site. In other words, the substrate must fit into the enzyme’s active site.
2. Cofactors and coenzymes affect enzyme function; this interaction relates to a structural change that alters the activity
rate of the enzyme. The enzyme may only become active when all the appropriate cofactors or coenzymes are present and bind to the appropriate sites on the enzyme.
✘ No specific cofactors or coenzymes are within the scope of the course and the AP Exam. c. Other molecules and the environment in which the enzyme
acts can enhance or inhibit enzyme activity. Molecules can bind reversibly or irreversibly to the active or allosteric sites, changing the activity of the enzyme.
d. The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/or presence of a competitive inhibitor.
Learning Objective:
LO4.17The student is able to analyze data to identify how molecular interactions affect structure and function. [See SP5.1]
Essential knowledge 4.B.2: Cooperative interactions within organisms promote efficiency in the use of energy and matter. (video)
a. Organisms have areas or compartments that perform a subset of functions related to energy and matter, and these parts contribute to the whole.
Evidence of student learning is a demonstrated understanding of each of the following:
1. At the cellular level, the plasma membrane, cytoplasm and, for eukaryotes, the organelles contribute to the overall specialization and functioning of the cell.
2. Within multicellular organisms, specialization of organs contributes to the overall functioning of the organism.
illustrative examples:
• Exchange of gases
• Circulation of fluids
• Digestion of food
• Excretion of wastes
3. Interactions among cells of a population of unicellular organisms can be similar to those of multicellular organisms, and these interactions lead to increased efficiency and utilization of energy and matter.To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Bacterial community in the rumen of animals
• Bacterial community in and around deep sea vents
Learning Objective:
LO4.18The student is able to use representations and models to analyze how cooperative interactions within organisms promote
efficiency in the use of energy and matter.
Essential knowledge 4.B.3: Interactions between and within populations influence patterns of species distribution and abundance (video).
a. Interactions between populations affect the distributions and abundance of populations.
Evidence of student learning is a demonstrated understanding of each of the following:
1. Competition, parasitism, predation, mutualism and commensalism can affect population dynamics.
2. Relationships among interacting populations can be characterized by positive and negative effects, and can be modeled mathematically (predator/prey, epidemiological models, invasive species).
3. Many complex symbiotic relationships exist in an ecosystem, and feedback control systems play a role in the functioning of these ecosystems.
✘ Specific symbiotic interactions are beyond the scope of the course and the AP Exam.
b. A population of organisms has properties that are different from those of the individuals that make up the population. The cooperation and competition between individuals contributes to these different properties.
c. Species-specific and environmental catastrophes, geological events, the sudden influx/depletion of abiotic resources or increased human activities affect species distribution and abundance.
illustrative examples:
• Loss of keystone species
• Kudzu
• Dutch elm disease
Learning Objective:
LO4.19The student is able to use data analysis to refine observations and measurements regarding the effect of population interactions on patterns of species distribution and abundance.
Essential knowledge 4.B.4: Distribution of local and global ecosystems changes over time (video).
a. Human impact accelerates change at local and global levels.
illustrative examples:
• Logging, slash and burn agriculture, urbanization, monocropping, infrastructure development (dams, transmission lines, roads), and global climate change threaten ecosystems and life on Earth.
• An introduced species can exploit a new niche free of predators or competitors, thus exploiting new resources.
• Introduction of new diseases can devastate native species.
Illustrative examples:
• Dutch elm disease
• Potato blight
• Small pox [historic example for Native Americans]
b. Geological and meteorological events impact ecosystem distribution.
Evidence of student learning is a demonstrated understanding of the following:
1. Biogeographical studies illustrate these changes.
illustrative examples:
• El Niño
• Continental drift
• Meteor impact on dinosaurs
Learning Objectives:
LO4.20The student is able to explain how the distribution of ecosystems changes over time by identifying large-scale events that have resulted in these changes in the past.
LO4.21The student is able to predict consequences of human actions on both local and global ecosystems.
Enduring understanding 4.C: Naturally occurring diversity among and between components within biological systems affects interactions with the environment.
Summary: A biological system that possesses many different components often has greater flexibility to respond to changes in its environment. This
phenomenon is sometimes referred to as “robustness.” Variation in molecular units provides cells with a wider range of functions; cells with
multiple copies of genes or heterozygous genes possess a wider range of functions compared to cells with less genetic diversity, while cells with myriad
enzymes can catalyze myriad chemical reactions.Environmental factors influence the phenotypic expression of an organism’s genotype. In humans, weight and height are examples of complex traits that can be influenced by environmental conditions. However, even simple single gene traits can be influenced by the environment; for example, flower color in some species of plants is dependent upon the pH of the environment. Some organisms possess the ability to respond flexibly to environmental signals to yield phenotypes that allow them to adapt to changes in the environment in which they live. Environmental factors such as temperature or density can affect sex determination in some animals, while parthenogenesis can be triggered by reproductive isolation. Plant seed dormancy can increase the survival of a species, and some viruses possess both lysogenic and lytic life cycles.The level of variation in a population affects its dynamics. The ability of a population to respond to a changing environment (fitness) is often measured in terms of genomic diversity. Species with little genetic diversity, such as a population of plants that reproduces asexually or a very small population exhibiting a genetic bottleneck effect, are at risk with regard to long-term success and survival. Diversity of species within an ecosystem may influence the stability of the ecosystem. Ecosystems with little species diversity are often less resilient to changes in the environment. Keystone species, predators, and
essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. For example, the removal of sea otters or mollusks can drastically affect a marine ecosystem, and the introduction of an exotic plant or animal species can likewise affect the stability of a terrestrial ecosystem.
Essential knowledge 4.C.1: Variation in molecular units provides cells with a wider range of functions (video).
a. Variations within molecular classes provide cells and organisms with a wider range of functions. To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Different types of phospholipids in cell membranes
• Different types of hemoglobin
• MHC proteins
• Chlorophylls
• Molecular diversity of antibodies in response to an antigen
b. Multiple copies of alleles or genes (gene duplication) may provide new phenotypes.
Evidence of student learning is a demonstrated understanding of each of the following:
1. A heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with two different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.
2. Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function.
illustrative example such as:
• The antifreeze gene in fish
Learning Objective:
LO4.22The student is able to construct explanations based on evidence of how variation in molecular units provides cells with a wider range of functions.
Essential knowledge 4.C.2: Environmental factors influence the expression of the genotype in an organism (video).
a. Environmental factors influence many traits both directly and indirectly.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Height and weight in humans
• Flower color based on soil pH
• Seasonal fur color in arctic animals
• Sex determination in reptiles
• Density of plant hairs as a function of herbivory
• Effect of adding lactose to a Lac + bacterial culture
• Effect of increased UV on melanin production in animals
• Presence of the opposite mating type on pheromones production in yeast and other fungi
b. An organism’s adaptation to the local environment reflects a flexible response of its genome.
illustrative examples:
• Darker fur in cooler regions of the body in certain mammal species
• Alterations in timing of flowering due to climate changes
Learning Objectives:
LO4.23The student is able to construct explanations of the influence of environmental factors on the phenotype of an organism.
LO4.24The student is able to predict the effects of a change in an environmental factor on the genotypic expression of the phenotype.
Essential knowledge 4.C.3: The level of variation in a population affects population dynamics (video).
a. Population ability to respond to changes in the environment is affected by genetic diversity. Species and populations with little genetic diversity are at risk for extinction.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• California condors
• Black-footed ferrets
• Prairie chickens
• Potato blight causing the potato famine
• Corn rust affects on agricultural crops
• Tasmanian devils and infectious cancer
b. Genetic diversity allows individuals in a population to respond differently to the same changes in environmental conditions.
illustrative examples:
• Not all animals in a population stampede.
• Not all individuals in a population in a disease outbreak are equally affected; some may not show symptoms, some may have mild symptoms, or some may be naturally immune and resistant to the disease.
c. Allelic variation within a population can be modeled by the HardyWeinberg equation(s).
Learning Objectives:
LO4.25The student is able to use evidence to justify a claim that a variety of phenotypic responses to a single environmental factor can result from different genotypes within the population.
LO4.26The student is able to use theories and models to make scientific claims and/or predictions about the effects of variation
within populations on survival and fitness.
Essential knowledge 4.C.4: The diversity of species within an ecosystem may influence the stability of the ecosystem (video).
a. Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to
changes in the environment. [See also 1.C.1]
b. Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. The effects
of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem, and when they are removed from the ecosystem, the ecosystem often collapses.
Learning Objective:
LO4.27The student is able to make scientific claims and predictions about how species diversity within an ecosystem influences ecosystem stability.