2nd Quarter>
LS1.A Feedback mechanisms
Feedback mechanisms maintain the internal environment within certain limits
1. Homeostasis refers to the (relatively) constant physiological state of the body. Even for simple organisms in relatively stable environments, the organism's metabolism will create a demand for regulatory mechanisms. (HS-LS1-3)
2. A stable physiological state (e.g. stable pH, electrolytes, fluid) is required for metabolic processes to operate properly and therefore for tissue and organ function. (HS-LS1-3)
3. Students should recognize that exercise increases both the demand for oxygen (to fuel cellular respiration) and the need to expel carbon dioxide (waste product of cellular respiration). The link between the respiratory system (where the gas exchanges occur at the gas exchange surface) and the cardiovascular system (which transports respiratory gases between exchange surfaces) should be understood. More able students will recognize that the muscular activity of exercise (like all metabolism) also produces other waste products (e.g. lactate and nitrogenous wastes) which are transported in the blood to regions where they can be metabolized (e.g. liver) or excreted (kidneys). (HS-LS1-3)
Feedback mechanisms can be positive or negative
4. Students should appreciate the reason for the paucity of positive feedback mechanisms in biological systems (being their inherent instability). This can be discussed with reference to specific examples (e.g. childbirth and fever). Students should be able to explain what brings about the cessation of the positive feedback loop and recognize that while some positive feedback has a particular physiological function, some can be pathological and fatal (e.g. shock caused by loss of blood volume). (HS-LS1-3)
5. Students should use an appropriate example (e.g. regulation of blood glucose) to explain how change from the steady state is detected and how negative feedback provides a self-correcting mechanism to prevent deviations from the steady state. A connection can be made to systems on different scales (e.g. population and ecosystem responses to disturbance) which are also regulated by negative feedback. (HS-LS1-3)
6. Students should recognize that animals maintain body temperature by using different strategies. They should distinguish between the constancy of the body temperature (homeothermy vs poikilothermy) and the source of the body heat (endogenous vs exogenous). Students should also be able to describe the mechanisms involved in heat production, conservation, and loss, and identify the degree of tolerance to fluctuations in body temperature. The usual mechanisms for thermoregulation in endothermic homeotherms are associated with metabolic activity and the skin (e.g shivering, vasoconstriction). The mechanisms for temperature regulation in strict ectotherms are largely behavioral. More able students may explain countercurrent heat exchangers, which can operate to cool or to warm blood depending on the species involved. In cold-adapted species, countercurrent flow works by way of warm blood in the arteries moving parallel and very close to the cooler venous return. The proximity of two fluids of different temperatures maintains the gradient for the exchange of heat. Heat is transferred from the warmer arterial flow into the cooler venous flow which then returns the warm blood to the body's core. The now somewhat cooler arterial flow proceeds to the relatively poorly insulated appendages. The net result is that the core remains warm and the appendages perpetually cool. Some tropical ungulates use a countercurrent system (the carotid rete) in the reverse manner to cool blood to the brain (crosscutting to MS-PS3.B, HS-PS3.B). (HS-LS1-3)
7. The insulin-glucagon system is one of the most easily explained homeostatic mechanisms. A rise in BG triggers insulin release and activates mechanisms (glycogenesis, cellular uptake of glucose) to decrease BG. A fall in BG triggers glucagon release and activates mechanisms (gluconeogenesis, glycogenolysis) to increase BG. Disorders of glucose metabolism provide a context for examining homeostatic mechanisms. Insulin production provides a classic case of technology developing solutions to problems (crosscutting to ETS1.B). In the case of insulin injection, technology provides the tools to restore cellular communication and enable cells to take up glucose. Urine analysis also provides a context for exploring technology associated with detecting and correcting homeostatic disorders. (HS-LS1-3)
8. Students should understand that, although water losses occur as a result of gas exchanges, transpiration is a necessary process in water (and mineral) uptake in plants. Gases move into and out of the mesophyll tissue by diffusion via stomata in leaves. Plants have mechanisms to regulate the turgor of the guard cells flanking each stoma and so too the size of the stomatal aperture. This provides another chance to emphasize the necessary interactions between the root and shoot systems (HS-LS1-3)
Crosscutting concepts
1. SC: Negative feedback can stabilize a system, whereas positive feedback can have a destabilizing effect. (HS-LS1-3)
Science and engineering practices
1. Use an evidence-based model to show how positive feedback operates.
SEP: Developing and using models (Not aligned to a performance expectation)
2. Use a model based on evidence to show how negative feedback mechanisms maintain homeostasis.
SEP: Developing and using models (HS-LS1-3)
3. Carry out an investigation to show how the body maintains homeostasis, for example, during exercise.
SEP: Planning and carrying out investigations (HS-LS1-3)
4. Carry out an investigation and analyze data to show how plants maintain water balance in changing environmental conditions.
SEP: Planning and carrying out investigations (HS-LS1-3)
5. Use mathematics and computational tools to support explanations of how organisms maintain homeostasis.
SEP: Using mathematics and computational thinking (Not aligned to a performance expectation)
Nature of Science
Scientific inquiry is characterized by a common set of values, including logical thinking, precision, open-mindedness, objectivity, repeatability of results, skepticism, and honesty. (HS-LS1-3)
LS1.B Growth and Development
Organisms grow and develop through mitosis
1. Students should be able to define multicellular and zygote and understand that mitotic division is responsible for the growth (increase in size) of a multicellular organism as well as in repair of tissues. (HS-LS1-4)
2. Students should recognize that mitosis is a relatively small part of the cell cycle and cells spend most of the cell cycle in interphase. Mitosis is the stage of nuclear division within the cell cycle. It is distinct from DNA replication (in interphase) and from division of the cytoplasm in cytokinesis. (HS-LS1-4)
3. Students should understand that, before a cell can divide, the DNA must be replicated so that each daughter cell receives a complete set of chromosomes. They should recognize the main events of mitosis in photographs or slides and describe what is happening, although they are not required to identify the stages by name. (HS-LS1-4)
i Prophase: Chromosomes condense and appear as chromatids. Mitotic spindle begins to form.
ii Metaphase: Mitotic spindle completed; it organizes the chromosomes at the equator of the cell.
iii Anaphase: Centromeres divide and chromatids separate to opposite poles as the spindle fibers to which they are attached shorten. Other spindle fibers lengthen to elongate the cell.
iv Telophase: Two new nuclei form.
4. The role of mitosis in specific cells and tissues in plants and animals should be recognized, e.g. meristems in plants and basal layer of skin in mammals. The role of mitosis in reproduction can be illustrated by the example of budding in yeast. (HS-LS1-4)
5. Students should understand that, before a cell can divide, the DNA must be replicated so that each daughter cell receives a complete set of chromosomes. They should recognize in photographs or slides the stage in mitosis when the chromosomes are separated to opposite poles prior to the cell dividing. (HS-LS1-4)
6. The semi-conservative model was verified by the Meselson-Stahl experiment. Students can work in pairs or small groups to replicate the basic findings of this experiment in the modeling activity (#86). Understanding that enzymes play an essential role in all stages of DNA replication is essential. The polarity of the DNA molecule has consequences for DNA synthesis, because DNA polymerase can only synthesize DNA in one direction by adding nucleotides to the 3' end of a DNA strand. The significance of (Okazaki) fragments, which are later joined, should be understood in this context. (HS-LS1-4)
Cells become differentiated to carry out specialized roles
7. Students should describe cellular differentiation as being the process by which a less specialized cell becomes more specialized. The role of gene regulation (selective switching on and off of genes during development) in this process should be recognized although knowledge of specific gene control mechanisms is not required. (HS-LS1-4)
8. Stem cells are characterized by self-renewal and potency. Different levels of cell potency can be recognized: totipotent, pluripotent (ESCs), and multipotent (ASCs). Tissue and organ repair provide a context within which to examine the features of stem cells and their potential. The areas of tissue engineering and stem cell technology also provide an ideal vehicle for exploring the role of technology in developing solutions to problems in health and medicine (crosscutting to ETS1.B). (HS-LS1-4)
9. Students should recall examples to illustrate the contribution of specialized cells to the formation of tissues. The role of multicellularity in division of labor and (consequently) functional efficiency can be discussed with reference to the same examples (deeper understanding relevant to HS-LS1-1). (HS-LS1-4)
Crosscutting concepts
1. SSM: Understand how models can be used to simulate DNA replication and mitosis to show how information flows within and between systems. (HS-LS1-4)
2. SF: The functions and properties of specialized cells can be inferred from their overall structure and the way their components are shaped and used. (Not aligned to a performance expectation)
Science and engineering practices
1. Use and evaluate a model to illustrate the semi-conservative replication of DNA.
SEP: Developing and using models (HS-LS1-4)
2. Evaluate the validity of experiments to determine how DNA is replicated.
SEP: Obtaining, evaluating, and communicating information (Not aligned to a performance expectation)
3. Use a model to show how mitosis and cellular differentiation are involved in producing and maintaining a multicellular organism.
SEP: Developing and using models (HS-LS1-4)
4. Use a model to show how the components of blood (a liquid tissue) are produced through cellular differentiation from stem cells.
SEP: Developing and using models (HS-LS1-4)
LS1.C Energy in Living Systems
Photosynthesis converts light energy into stored chemical energy
1. ATP is a phosphorylated nucleotide and stores its energy in the form of a high energy phosphate bond. Students should understand that hydrolysis of ATP is exergonic and releases free energy (crosscutting to HS-PS3.B, HS-PS3.D). (HS_LS1-7)
2. Students should recognize that there are two phases in photosynthesis. The first (light dependent) reactions are concerned with the capture of light energy by chlorophylls in the thylakoid membranes, with the generation of ATP and reducing power (NAHPH). The second set of reactions (light independent reactions) use the ATP and NADPH to generate glucose in the stroma (liquid interior) of the chloroplast. Students should appreciate that the systems that capture the light are membrane-bound. The importance of chloroplast structure in compartmentalizing the reactions should be appreciated by all students. (HS-LS1-5)
3. Students should understand that photosynthesis is an endothermic redox reaction overall, and needs a source of energy (sunlight) and electrons (from the hydrolysis of water). (HS-LS1-5)
Glucose can be used to make other macromolecules
4. Students should be able to explain, through basic examples, that the carbon, hydrogen, and oxygen atoms in glucose form the basis of all other carbon-based molecules in organisms. Carbon can share pairs of electrons with as many as four other atoms to form organic molecules of several configurations. (HS-LS1-6)
5. Monosaccharides, particularly glucose, are a major fuel for cellular work. They also function as the raw material for the synthesis of other monomers, such as amino acids and fatty acids. (HS-LS1-6) Hydrocarbons consist of a C-H-only backbone and are quite stable. Functional groups are atoms or groups of atoms covalently bonded to a carbon backbone. They give molecules specific properties. Carbon-based molecules can be reconfigured and new types of molecules made via enzyme-based reactions such as:
– Functional-group transfer from one molecule to another
– Electron transfer from one molecule to another
_ Rearrangement of internal bonds
_ Condensation of two molecules into one
– Cleavage of one molecule into two by hydrolysis
Students should appreciate that complex metabolic pathways, in which each step is catalyzed by enzymes, are involved in making different types of molecules from glucose. For example, the pentose phosphate pathway oxidizes glucose to make NADPH and other carbohydrates, including ribose, for biosynthesis.
Matter and energy flow between different living systems
6. Cellular respiration is a catabolic, energy yielding pathway, whereas photosynthesis is an anabolic process that transforms sunlight energy into chemical energy. ATP is central to these energy transformations in cells, being the universal energy carrier in cells (crosscutting to HS-PS3.B, HS-PS3.D). (HS-LS1-7)
7. Students should describe glycolysis as the major anaerobic pathway in cells with a net yield of 2ATP and 2NADH2. In the absence of oxygen, various anaerobic pathways (alcoholic fermentation, lactic acid fermentation) metabolize the pyruvate. Students should understand that cellular respiration in the mitochondrion is an aerobic process, which yields ATP and produces carbon dioxide. Oxygen is the terminal oxygen acceptor. More able students will recognize that the production of reducing power in glycolysis and the Krebs cycle is central to the stepwise oxidation of glucose. (HS-LS1-7)
8. Students should recognize that glycolysis occurs in the cytoplasm and that pyruvate enters the mitochondrion. They should associate regions of the mitochondrion with specific parts of the cellular respiration process: the link reaction and Krebs cycle in the matrix, and ETC in the cristae. (HS-LS1-7)
Heat is released during chemical reactions
9. The energy transfers in biological systems (which are often effectively losses from the system) are not very efficient. For example, only about 40% of the energy contained in glucose is transferred to ATP (usable energy). The rest (around 60%) is lost from the system as heat, and it is this waste heat that warms the body. Students should be able to transfer this knowledge to their understanding of energy transfers in ecosystems (crosscutting to HS-PS3.B, HS-PS3.D). (HS-LS1-7)
Crosscutting concepts
1. EM: Changes of energy and matter in a system (e.g. cell) can be described in terms of energy and matter movements into, out of, and within that system. (HS-LS1-5) (HS-LS1-6)
2. Energy cannot be created or destroyed; it only moves between one place and another, e.g. between cells or between organisms and their environment. (HS-LS1-7)
3. The structure of organelles tells us about their role in the cell. (Not aligned to a performance expectation)
Science and engineering practices
1. Use a model to show how ATP provides energy to carry out life's functions.
SEP: Developing and using models (HS-LS1-5)
2. Use a model to show how photosynthesis transforms light energy into stored chemical energy.
SEP: Developing and using models (HS-LS1-5)
3. Based on evidence, explain the fate of glucose in living systems.
SEP: Constructing explanations and designing solutions (HS-LS1-6)
4. Use a model based on evidence to show understanding of cellular respiration.
SEP: Developing and using models (HS-LS1-7)
5. Conduct an investigation to demonstrate that light drives photosynthesis.
SEP: Planning and carrying out investigations (Not aligned to a performance expectation)
6. Conduct an investigation to show that respiration uses oxygen and produces CO2.
SEP: Planning and carrying out investigations (Not aligned to a performance expectation)
LS2.A Interdependence in Ecosystems
Species have interdependent relationships in ecosystems
1. A population (all the organisms that both belong to the same species and live in the same geographical area) is distinct from a community (a group of interacting species sharing an environment). The community (biotic factors) and the physical environment (abiotic factors) together form an ecosystem. (HS-LS2-1)
2. The fundamental niche of an organism is a multidimensional ecological space, but the extent to which that space is occupied (the realized niche) is a function of direct and indirect interactions with other organisms (e.g. competition). Intraspecific competition tends to broaden niches (with some individuals faring better than others) whereas interspecific competition tends to drive niche differentiation (HS-LS2-1, HS-LS2-2)
3. Students should recognize that the characteristics of populations, such as birth rate and age structure, are not shown by the individuals themselves. The distribution patterns of populations are determined both by habitat and resource availability, and the reproductive, social, and dispersal strategies of the organisms themselves. This is best explained using clear examples, such as the spread of weeds (e.g. spread of Kudzu in the southern USA), the distribution of social species (e.g. prairie dogs or marmots), or the distribution of desert plants (e.g. saguaro cacti). When species don't interact, distributions will tend to be random, sociality creates clumped distributions, and regular distribution patterns arise when species are territorial or individuals avoid each other. These influences will be reinforced or dampened by the environment, e.g. an environment with patchy resources will foster a clumped distribution. (HS-LS2-2)
4. Students should be able to describe the different ways in which species interact and, using examples, identify the interactions as neutral for one or both parties, beneficial to one or both parties, or detrimental to one or both parties. Students should be able to cite at least one example of each of the interspecific interactions listed and explain the relationship. Local examples provide good opportunity for discussion. (HS-LS2-2)
5. Both intraspecific and interspecific competition will limit population sizes if resources are limiting. For species sharing some resources (e.g. some food sources), resource limitation will constrain the breeding success of both species populations. Intraspecific competition has a greater constraining effect on population size than interspecific competition because members of a same species have the same resource use curve. In species where scramble competition predominates, resource limitation can result in most of the population not surviving. In many insects and mass spawning vertebrates particularly, this can constrain breeding to certain tight time frames, e.g. in monarchs, larvae hatching from eggs laid late in the season will have high mortality as a result of lack of food. In species where contest competition predominates, the effect on population size may be less because subordinate individuals may not breed anyway. (HS-LS2-1, HS-LS2-2)
6. Actual or realized niches will be constrained by interspecific competition. Niche overlap will be less where competition for shared resources is strong. The role of interspecific competition in increasing community diversity can be discussed with reference to niche specialization and the presence of a greater number of narrower niches (see activity #122). Students should consider the role of resource competition in shaping communities over long periods of time (i.e. by evolution). They may also contrast this with competitive exclusion, as often occurs following novel introductions (activity #121 and cross reference to 'The Dynamic Ecosystem", activity #163). (HS-LS2-2)
7. Students should understand that carrying capacity is not a static figure but may vary seasonally and as species assemblages change. Students should consider how long term climate shifts may alter carrying capacity for vulnerable ecosystems. Carrying capacity is ultimately determined by productivity, and changes in climate and the resource use will alter the population capacity that can be sustainably supported. (HS-LS2-1)
8. Students should be able to explain the relationship between the size of a home range and the resources it contains and use examples to illustrate this. Students should understand that home ranges, unlike territories, are not defended although the resources they contain will determine the population size that can be supported. Core areas, such as those discussed in activity #127, are similar to territories in that they are defended. (HS-LS2-1)
9. Students should understand how the resource availability limits the size to which a (potentially exponentially increasing) population can grow. There are links that could be made here to Darwin's theory of evolution by natural selection (crosscutting to LS4.C). (HS-LS2-2)
Crosscutting concepts
1. SPQ: How a factor, such as competition or climate, affects an ecosystem's carrying capacity depends on the scale at which it occurs. (HS-LS2-1)
2. SPQ: A model of how specific factors affect biodiversity and population growth at one scale can be used to understand systems at other scales. (HS-LS2-2)
3. CE: Empirical evidence helps us make claims about cause and effect in studies of population interaction and population growth and decline. (Not aligned to a performance expectation)
Science and engineering practices
1. Use a model based on evidence to show how competition limits population size.
SEP: Developing and using models (Not aligned to a performance expectation)
2. Explain, based on evidence, how different species reduce resource competition.
SEP: Constructing explanations and designing solutions (Not aligned to a performance expectation)
3. Use mathematical representations to support explanations of factors affecting carrying capacity.
SEP: Using mathematics and computational thinking (HS-LS2-1)
4. Use mathematical representations to support and revise explanations based on evidence about factors affecting population growth.
SEP: Using mathematics and computational thinking (Not aligned to a performance expectation)
5. Use a model to illustrate exponential population growth.
SEP: Developing and using models (Not aligned to a performance expectation)
6. Plan and carry out an investigation of exponential growth in bacteria.
SEP: Planning and carrying out investigations (Not aligned to a performance expectation)
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