This is a resource post for anyone interested in the new AP Biology curriculum framework and how it talks about energy. I just went through the document and copy-n-pasted almost all the references to energy. (I tried to delete exact duplicates.) Maybe this can help us understand what "free energy" means to the College Board, and if there are other kinds of energy besides free energy that are important to understand in the context of AP Biology.
Other intriguing terms I see here are: entropy; energy-capturing process; energy availability; high energy electrons; metabolic fitness; and metabolic strategies. I would guess that the average--or even above-average--AP Biology teacher might struggle to define or give examples of some of these concepts. I would bet there might be a market for professional development on understanding and teaching these ideas.
The formatting has been completely lost (note the use of passive voice and third person to obscure agency here), so the hierarchy of Big Ideas, Enduring Whatsits, and Essential Doodads might be somewhat unclear. You can always refer to the original document here.
Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.
Other intriguing terms I see here are: entropy; energy-capturing process; energy availability; high energy electrons; metabolic fitness; and metabolic strategies. I would guess that the average--or even above-average--AP Biology teacher might struggle to define or give examples of some of these concepts. I would bet there might be a market for professional development on understanding and teaching these ideas.
The formatting has been completely lost (note the use of passive voice and third person to obscure agency here), so the hierarchy of Big Ideas, Enduring Whatsits, and Essential Doodads might be somewhat unclear. You can always refer to the original document here.
Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.
Living systems require free energy and matter to maintain order, grow and reproduce. Organisms employ various strategies to capture, use and store free energy and other vital resources. Energy deficiencies are not only detrimental to individual organisms; they also can cause disruptions at the population and ecosystem levels.
Autotrophic cells capture free energy through photosynthesis and chemosynthesis. Photosynthesis traps free energy present in sunlight that, in turn, is used to produce carbohydrates from carbon dioxide. Chemosynthesis captures energy present in inorganic chemicals. Cellular respiration and fermentation harvest free energy from sugars to produce free energy carriers, including ATP. The free energy available in sugars drives metabolic pathways in cells. Photosynthesis and respiration are interdependent processes.
Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.
Living systems require energy to maintain order, grow and reproduce. In accordance with the laws of thermodynamics, to offset entropy, energy input must exceed energy lost from and used by an organism to maintain order. Organisms use various energy-related strategies to survive; strategies include different metabolic rates, physiological changes, and variations in reproductive and offspring-raising strategies. Not only can energy deficiencies be detrimental to individual organisms, but changes in free energy availability also can affect population size and cause disruptions at the ecosystem level.
Several means to capture, use and store free energy have evolved in organisms. Cells can capture free energy through photosynthesis and chemosynthesis. Autotrophs capture free energy from the environment, including energy present in sunlight and chemical sources, whereas heterotrophs harvest free energy from carbon compounds produced by other organisms. Through a series of coordinated reaction pathways, photosynthesis traps free energy in sunlight that, in turn, is used to produce carbohydrates from carbon dioxide and water. Cellular respiration and fermentation use free energy available from sugars and from interconnected, multistep pathways (i.e., glycolysis, the Krebs cycle and the electron transport chain) to phosphorylate ADP, producing the most common energy carrier, ATP. The free energy available in sugars can be used to drive metabolic pathways vital to cell processes. The processes of photosynthesis and cellular respiration are interdependent in their reactants and products.
Essential knowledge 2.A.1: All living systems require constant input of free energy.
1. Order is maintained by constant free energy input into the system.
2. Loss of order or free energy flow results in death.
3. Increased disorder and entropy are offset by biological processes that maintain or increase order.
Living systems do not violate the second law of thermodynamics, which states that entropy increases over time.
1. Order is maintained by coupling cellular processes that increase entropy (and so have negative changes in free energy) with those that decrease entropy (and so have positive changes in free energy).
2. Energy input must exceed free energy lost to entropy to maintain order and power cellular processes.
3. Energetically favorable exergonic reactions, such as ATP→ADP, that have a negative change in free energy can be used to maintain or increase order in a system by being coupled with reactions that have a positive free energy change.
Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway. • Krebs cycle • Glycolysis • Calvin cycle • Fermentation
d. Organisms use free energy to maintain organization, grow and reproduce.
1. Organisms use various strategies to regulate body temperature and metabolism.
• Endothermy (the use of thermal energy generated by metabolism to maintain homeostatic body temperatures)
• Ectothermy (the use of external thermal energy to help regulate and maintain body temperature)
• Elevated floral temperatures in some plant species
2. Reproduction and rearing of offspring require free energy beyond that used for maintenance and growth. Different organisms use various reproductive strategies in response to energy availability.
• Seasonal reproduction in animals and plants
• Life-history strategy (biennial plants, reproductive diapause)
3. There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms — generally, the smaller the organism, the higher the metabolic rate.
4. Excess acquired free energy versus required free energy expenditure results in energy storage or growth.
5. Insufficient acquired free energy versus required free energy expenditure results in loss of mass and, ultimately, the death of an organism.
Changes in free energy availability can result in changes in population size.
Changes in free energy availability can result in disruptions to an ecosystem.
• Change in the producer level can affect the number and size of other trophic levels.
• Change in energy resources levels such as sunlight can affect the number and size of the trophic levels.
Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.
a. Autotrophs capture free energy from physical sources in the environment.
1. Photosynthetic organisms capture free energy present in sunlight.
2. Chemosynthetic organisms capture free energy from small inorganic molecules present in their environment, and this process can occur in the absence of oxygen.
b. Heterotrophs capture free energy present in carbon compounds produced by other organisms.
1. Heterotrophs may metabolize carbohydrates, lipids and proteins by hydrolysis as sources of free energy.
2. Fermentation produces organic molecules, including alcohol and lactic acid, and it occurs in the absence of oxygen.
c. Different energy-capturing processes use different types of electron acceptors.
• NADP+ in photosynthesis • Oxygen in cellular respiration
d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.
1. During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II.
2. Photosystems I and II are embedded in the internal membranes of chloroplasts (thylakoids) and are connected by the transfer of higher free energy electrons through an electron transport chain (ETC).
3. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thykaloid membrane is established.
3. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thykaloid membrane is established.
4. The formation of the proton gradient is a separate process, but it is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase.
5. The energy captured in the light reactions as ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the chloroplast.
f. Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that harvest free energy from simple carbohydrates.
1. Glycolysis rearranges the bonds in glucose molecules, releasing free energy to form ATP from ADP and inorganic phosphate, and resulting in the production of pyruvate.
g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.
h. Free energy becomes available for metabolism by the conversion of ATP→ADP, which is coupled to many steps in metabolic pathways.
Passive transport does not require the input of metabolic energy because spontaneous movement of molecules occurs from high to low concentrations; examples of passive transport are osmosis, diffusion, and facilitated diffusion. Active transport requires metabolic energy and transport proteins to move molecules from low to high concentrations across a membrane.
Translation involves energy and many steps, including initiation, elongation and termination.
Some genes are continually expressed, while the expression of most is regulated; regulation allows more efficient energy utilization, resulting in increased metabolic fitness.
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.
Mitochondria specialize in energy capture and transformation.
Chloroplasts are specialized organelles found in algae and higher plants that capture energy through photosynthesis. 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.
Energy flows, but matter is recycled.
Many adaptations of organisms are related to obtaining and using energy and matter in a particular environment.
Cooperation within organisms increases efficiency in the use of matter and energy.
Essential knowledge 4.B.2: Cooperative interactions within organisms promote efficiency in the use of energy and matter.
Organisms have areas or compartments that perform a subset of functions related to energy and matter, and these parts contribute to the whole.
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.
Energy in the Science Practices
The student is able to measure and collect experimental data with respect to volume, size, mass, temperature, pH, etc. In addition, the student can estimate energy procurement and utilization in biological systems, including ecosystems.
The student is able to measure and collect experimental data with respect to volume, size, mass, temperature, pH, etc. In addition, the student can estimate energy procurement and utilization in biological systems, including ecosystems.
The student draws on information from other sciences to explain biological processes; examples include how the conservation of energy affects biological systems;
Energy in sample test questions:
11. Which of the following statements most directly supports the claim that different species of organisms use different metabolic strategies to meet their energy requirements for growth, reproduction, and homeostasis?
(A) During cold periods pond-dwelling animals can increase the number of unsaturated fatty acids in their cell membranes while some plants make antifreeze proteins to prevent ice crystal formation in tissues.
(B) Bacteria lack introns while many eukaryotic genes contain many of these intervening sequences.
(C) Carnivores have more teeth that are specialized for ripping food while herbivores have more teeth that are specialized for grinding food.
(D) Plants generally use starch molecules for storage while animals use glycogen and fats for storage.
16. Additional observations were made on day 21, and no yellow-leaved seedlings were found alive in either dish. This is most likely because
(A) yellow-leaved seedlings were unable to absorb water from the paper towels
(B) taller green-leaved seedlings blocked the light and prevented photosynthesis
(C) yellow-leaved seedlings were unable to convert light energy to chemical energy
(D) a higher rate of respiration in yellow-leaved seedlings depleted their stored nutrients
29. Experimental evidence shows that the process of glycolysis is present and virtually identical in organisms from all three domains, Archaea, Bacteria, and Eukarya. Which of the following hypotheses could be best supported by this evidence?
(A) All organisms carry out glycolysis in mitochondria.
(B) Glycolysis is a universal energy-releasing process and therefore suggests a common ancestor for all forms of life.
(C) Across the three domains, all organisms depend solely on the process of anaerobic respiration for ATP production.
(D) The presence of glycolysis as an energy-releasing process in all organisms suggests that convergent evolution occurred.
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