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Biology Chapter 6

Biology Chapter 6 - 6.1 Cells and the Flow of Energy A...

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6.1 Cells and the Flow of Energy A. Forms of Energy 1. Energy is capacity to do work; cells continually use energy to develop, grow, repair, reproduce, etc. 2. Kinetic energy is energy of motion ; all moving objects have kinetic energy. 3. Potential energy is stored energy. 4. Food is chemical energy ; it contains potential energy. 5. Chemical energy can be converted into mechanical energy , e.g., muscle movement. B. Two Laws of Thermodynamics 1. First law of thermodynamics (also called the law of conservation of energy ) a. Energy cannot be created or destroyed, but it can be changed from one form to another. b. In an ecosystem, solar energy is converted to chemical energy by the process of photosynthesis; some of the chemical energy in the plant is converted to chemical energy in an animal, which in turn can become mechanical energy or heat loss. c. Neither the plant nor the animal create energy, they convert it from one form to another. d. Likewise, energy is not destroyed; some becomes heat that dissipates into the environment. 2. Second law of thermodynamics a. Energy cannot be changed from one form into another without a loss of usable energy. b. Heat is a form of energy that dissipates into the environment; heat can never be converted back to another form of energy. C. Cells and Entropy 1. Every energy transformation makes the universe less organized and more disordered; entropy is the term used to indicate the relative amount of disorganization. 2. When ions distribute randomly across a membrane, entropy has increased. 3. Organized/usable forms of energy (as in the glucose molecule) have relatively low entropy; unorganized/less stable forms have relatively high entropy. 4. Energy conversions result in heat; therefore, the entropy of the universe is always increasing. 5. Living things depend on a constant supply of energy from the sun, because the ultimate fate of all solar energy in the biosphere is to become randomized in the universe as heat; the living cell is a temporary repository of order purchased at the cost of a constant flow of energy. 6.2 Metabolic Reactions and Energy Transformations 1. Metabolism is the sum of all the biochemical reactions in a cell. 2. In the reaction A + B = C + D, A and B are reactants and C and D are products . 3. Free energy (D G ) is the amount of energy that is free to do work after a chemical reaction. 4. Change in free energy is noted as D G ; a negative D G means that products have less free energy than reactants; the reaction occurs spontaneously. 5. Exergonic reactions have a negative D G and energy is released.
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6. Endergonic reactions have a positive D G ; products have more energy than reactants; such reactions can only occur with an input of energy.
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Biology Chapter 6 - 6.1 Cells and the Flow of Energy A...

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