BSC 314 Lecture 22: Energy Defined
27 Jun 2018
School
Department
Course
Professor
Energy Defined
Energy is the capacity to do work. It is the flow of energy that makes the work of life
(metabolism) possible. From the smallest unit of life—the cell—to the largest organism,
all living things obtain, modify, expend, and release energy and in doing so adhere to
very explicit energy laws of the universe.
Of the tremendous amount of energy received from the sun, less than 1 percent is
captured by green plants and converted through photosynthesis to usable energy.
Some solar energy drives the geological processes that make the earth habitable for
organisms then is lost back into space. Fully a third never makes it through the Earth's
atmosphere to reach the surface. The small percentage that is captured in
photosynthesis runs the entire Earth ecosystem.
Laws of Thermodynamics
Universal laws of energy exchange, the laws of thermodynamics, govern all
interactions among organisms (and all matter). Two are especially important in
explaining how organisms manage their energy needs.
First Law of Thermodynamics—the conservation of energy—simply states that
while the form of energy can be changed, energy itself can neither be created nor
destroyed. Energy exists in two forms: potential energy (stored
energy available to do work) and kinetic energy (the energy used to dowork).
Second Law of Thermodynamics—the law of entropy (disorder)—in brief, states
that chemical reactions run downhill, i.e., the products of the reaction always
have less potential energy than the original reactants. Entropy measures the
randomness or disorder that forever increases in systems to which no energy is
added.
In each energy exchange—from the first photosynthetic reaction to the last in the food
web where carnivores dine on one another—energy escapes, primarily as heat.
Although the heat energy remains in the system (fulfilling the First Law of conservation),
the energy is no longer available to do work, hence it is “lost” to further metabolism.
Each of the exchanges is exergonic (ex = out; energy out). The heat of the system rises
in proportion to the loss of potential energy. To maintain the organized systems like
organisms, therefore, energy is added constantly in a series of endergonic (end = in;
energy in) processes.
Membranes: Reception, Communication
Some of the proteins embedded in the phospholipid bilayer are receptors that receive a
signal molecule. This molecule contains a message that is transmitted to another
molecule, usually with instructions to perform some action. Some of the signal
molecules pass through the membrane in ways described above, but many rely on
membrane receptors to conduct the instructions to secondary messengers within the
cell, a process of signal transduction (changing the molecular form of the signal). The
secondary messengers then pass the transduced signal to the activator cells, which
carry out the function.
Document Summary
It is the flow of energy that makes the work of life (metabolism) possible. From the smallest unit of life the cell to the largest organism, all living things obtain, modify, expend, and release energy and in doing so adhere to very explicit energy laws of the universe. Of the tremendous amount of energy received from the sun, less than 1 percent is captured by green plants and converted through photosynthesis to usable energy. Some solar energy drives the geological processes that make the earth habitable for organisms then is lost back into space. Fully a third never makes it through the earth"s atmosphere to reach the surface. The small percentage that is captured in photosynthesis runs the entire earth ecosystem. Universal laws of energy exchange, the laws of thermodynamics, govern all interactions among organisms (and all matter). Two are especially important in explaining how organisms manage their energy needs.
