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AP Biology Notes Outline Enduring Understanding 2.A Big Idea 2

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AP Biology Notes Outline Enduring Understanding 2.A Big Idea 2 AP Biology Notes Outline Enduring Understanding 2.A Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring Understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter. Learning Objectives: Essential Knowledge 2.A.1: All living systems require constant input of free energy. – (2.1) The student is able to explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce. – (2.2) The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems. – (2.3) The student is able to predict how changes in free energy availability affect organisms, populations and ecosystems. Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes. – (2.4) The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy. – (2.5) The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy. Essential Knowledge 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization. – (2.6) The student is able to use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion. – (2.7) The student is able to explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. – (2.8) The student is able to justify the selection of data regarding the types of molecules that an animal, plant or bacterium will take up as necessary building blocks and excrete as waste products. – (2.9) The student is able to represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction. Required Readings: Textbook Ch. 8 (pp. 142-151); Textbook Ch. 40 (pp. 862 & 868-872); Textbook Ch. 54 (pp. 1205-1210) Textbook Ch. 9; Textbook Ch. 10 Textbook Ch. 55 (pp. 1231-1234); Textbook Ch. 3 (pp. 46-52); Textbook Ch. 6 (pp. 98-99) Article: Surface Area-to-Volume Ratio in Cells Practicing Biology Homework Questions: Questions #1-21 Essential Knowledge 2.A.1: All living systems require constant input of free energy. 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 that 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 can also affect population size and cause disruptions at the ecosystem level. The concepts of metabolism help us to understand how matter and energy flow during life’s processes and how that flow is regulated in living systems. Metabolism is the totality of an organism’s chemical reactions: • An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics. • Metabolism is an emergent property of life that arises from interactions between molecules within the cell. • A metabolic pathway begins with a specific molecule and ends with a product, whereby each step is catalyzed by a specific enzyme. L. Carnes Bioenergetics is the study of how organisms manage their energy resources. • Catabolic pathways release energy by breaking down complex molecules into simpler compounds: cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism. • Anabolic pathways consume energy to build complex molecules from simpler ones: the synthesis of protein from amino acids is an example of anabolism. Energy is the capacity to cause change. Energy cannot be created or destroyed, but can be converted from one form to another. Energy exists in various forms, some of which can perform work: • Kinetic energy is energy associated with motion. • Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules. • Potential energy is energy that matter possesses because of its location or structure. • Chemical energy is potential energy available for release in a chemical reaction. Thermodynamics is the study of energy transformations. A closed system, such as that approximated by liquid in a thermos, is isolated from its surroundings. In an open system, energy and matter can be transferred between the system and its surroundings. Organisms are open systems. According to the first law of thermodynamics, the energy of the universe is constant: energy can be transferred and transformed, but it cannot be created or destroyed. The first law is also called the principle of conservation of energy. During every energy transfer or transformation, some energy is unusable, and is often lost as heat. According to the second law of thermodynamics: every energy transfer or transformation increases the entropy (disorder) of the universe. Living cells unavoidably convert organized forms of energy to heat. Spontaneous processes occur without energy input; they can happen quickly or slowly. For a process to occur without energy input, it must increase the entropy of the universe. Living systems do not violate the second law of thermodynamics, which states that entropy increases over time: • Energy flows into an ecosystem in the form of light and exits in the form of heat. 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). • Energy input must exceed free energy lost to entropy to maintain order and power cellular processes. Cells create ordered structures from less ordered materials. Organisms also replace ordered forms of matter and energy with less ordered forms. • The evolution of more complex organisms does not violate the second law of thermodynamics. Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases. Living systems increase the entropy of their surroundings, as predicted by thermodynamic law. Therefore, the evolution of biological order is perfectly consistent with the laws of thermodynamics. Biological Example: An animal obtains starch, proteins, and other complex molecules from the food it eats. As catabolic pathways break down these molecules, the animal releases carbon dioxide and water (small molecules that possess less energy than the food did). The depletion of chemical energy is accounted for by heat generated during metabolism. The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously. Biologists often want to know which reactions occur spontaneously and which require input of energy. To do so, they need to determine energy changes that occur in chemical reactions. A living system’s free energy is energy that can do work when temperature and pressure are uniform, as in a living cell. • The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T): ∆G = ∆H – T∆S • Only processes with a negative ∆G are spontaneous. Spontaneous processes can be harnessed to perform work. • G system’s quantity of free energy; H system’s total energy; T absolute temperature in Kelvin; S system’s total entropy • So, for a process to occur spontaneously, the system must either give up energy (decrease H), give up order (increase S), or both. The change in G must be negative. In other words, nature runs downhill in the sense of a loss of useful energy – the capacity to perform work. Free energy is a measure of a system’s instability, its tendency to change to a more stable state. During a spontaneous change, free energy decreases and the stability of a system increases. Equilibrium is a state of maximum stability. A process is spontaneous and can perform work only when it is moving toward equilibrium. The concept of free energy can be applied to the chemistry of life’s processes: • An exergonic reaction proceeds with a net release of free energy and is spontaneous (∆G is negative). • An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous (∆G is positive). Exergonic Reaction: ΔG < 0…reaction proceeds with a net RELEASE of free energy…these reactions occur spontaneously. Endergonic Reaction: ΔG > 0…reaction proceeds with an ABSORPTION of free energy…these reactions are not spontaneous. ATP powers cellular work by coupling exergonic reactions to endergonic reactions. A cell does three main kinds of work: chemical, transport and mechanical. To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one. Most energy coupling in cells is mediated by ATP using the chemical potential energy stored in the bonds of an ATP molecule. ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP). The energy to phosphorylate ADP comes from catabolic reactions in the cell. In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction. Overall, the coupled reactions are exergonic. The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis. Energy is released from ATP when the terminal phosphate bond is broken.
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