Chapter 7:
Energy and Metabolism
© Cengage Learning 2015
SOLOMON • MARTIN • MARTIN • BERG
BIOLOGY
tenth edition
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Energy Conversion
Cells obtain energy in many forms, and have mechanisms that convert energy from one form to another
Radiant energy is the ultimate source of energy for life
Photosynthetic organisms capture about 0.02% of the sun’s energy that reaches Earth, and convert it to chemical energy in bonds of organic molecules
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7.1 Biological Work
Matter: anything that has mass and takes up space
Energy: the capacity to do work (change in state or motion of matter)
Expressed in units of work (kilojoules, kJ) or units of heat energy (kilocalories, kcal)
1 kcal = 4.184 kJ
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Potential Energy and Kinetic Energy
Potential energy: capacity to do work as a result of position or state
Kinetic energy: energy of motion is used, work is performed
POTENTIAL
Energy of position
KINETIC
Energy of motion
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Figure 7-1 Potential versus kinetic energy
The potential chemical energy released by cellular respiration is converted to kinetic energy in the muscles, which do the work of drawing the bow. The potential energy stored in the drawn bow is transformed into kinetic energy as the bowstring pushes the arrow toward its target.
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Organisms Carry Out Conversions Between Potential/Kinetic Energy
Most actions involve a series of energy transformations that occur as kinetic energy is converted to potential energy – or potential energy to kinetic energy
Chemical energy: potential energy stored in chemical bonds
Example: Chemical energy of food molecules is converted to mechanical energy in muscle cells
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7.2 The Laws of Thermodynamics
Thermodynamics governs all activities of the universe, from cells to stars
Biological systems are open systems that exchange energy with their surroundings
Closed
system
Closed
system
Surroundings
Surroundings
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Figure 7-2 Closed and open systems
A closed system does not exchange energy with its surroundings.
(b) An open system exchanges energy with its surroundings.
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The First Law of Thermodynamics
Energy cannot be created or destroyed
Energy can be transferred or converted from one form to another, including conversions between matter and energy
The energy of any system plus its surroundings is constant
Organisms must capture energy from the environment and transform it to a form that can be used for biological work
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The Second Law of Thermodynamics
When energy is converted from one form to another, some usable energy (energy available to do work) is converted into heat that disperses into the surroundings
As a result, the amount of usable energy available to do work in the universe decreases over time
Heat: the kinetic energy of randomly moving particles
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Entropy
The measure of the disorder or randomness of energy
Organized, usable energy ...