6.4 Electric Fields in Biology
187
6.4 Electric Fields in Biology
Because of the essential importance of electric interactions in biological systems,
strong electric fields in the vicinity of life systems can have overwhelming
consequences. So far, none of the extensive electromagnetic and quantum theory
predictions disagree with experiments. With such agreement over wide realms, we
expect that all observed properties of biochemical systems, including molecular
structure and biochemical reactions, as well as the nature of the electrical pulses
used by advanced biological organisms to transfer information between subsystems,
follow current theory.
Most biological materials are close to neutral in charge. This fact comes about
because in the temperature range within which water is liquid, oppositely charged
particles can stay bound together. Electric interactions dominate the force between
such charges, and it typically takes several electron volts of energy to pull a negative
charge from a positive one when they are initially separated by atomic distances. The
energy available by thermal collisions is about 1/25 eV. Life systems use electric
forces present in molecular and chemical interactions to do purposeful work by
pulling charges around.
Our everyday experience with electricity comes from the transfer of a very small
fraction of the charge from one body to another. The flux of one tenth of a trillionth
of a percent of your electrons traveling as a spark from your finger to a doorknob
can produce a painful searing of a nerve ending. (If the gap was half a centimeter,
the electric potential from finger to knob would have been about 15,000 V.) At
the microscopic level in biology, electric fields arise when charges are separated,
such as within molecules (giving them an “electric polarization”), by cell walls,
through biochemical reactions of molecules and ions, between ions in solutions,
and by ion pumps in cell walls. Some molecules, like water, have built-in electric
polarization. The strongly polarized water molecules make water a good solvent
for other polarized molecules and ionic salts. Other molecules become polarized by
being stressed in external electric fields (“induced electric polarization”). Charge
separation and transfer is often used in life systems to drive biochemical reactions.
Even so, electric forces in biosystems tend to be limited in range, because within
the protoplasm of our cells, excess charge on a molecule will attract ions of
the opposite charge, shielding the molecule from other long-range electric forces.
However, significant charge separation can be maintained across cell membranes.
Even so, the change in the electric potential across a resting nerve cell is only
about 0.07 V.
The strength of an electric field is not normally reported in newtons per coulomb,
but rather in volts per meter, in deference to the importance of energy. Energy is
exchanged whenever the action of an electric field causes a charge to moves over
some distance. If the field pushes the charge over some distance, the charge gains
energy taken from the agent producing the electric field. The energy gained by a
unit test charge is call the ‘electric potential’, V . Inversely, the electric field is
187
6.4 Electric Fields in Biology
Because of the essential importance of electric interactions in biological systems,
strong electric fields in the vicinity of life systems can have overwhelming
consequences. So far, none of the extensive electromagnetic and quantum theory
predictions disagree with experiments. With such agreement over wide realms, we
expect that all observed properties of biochemical systems, including molecular
structure and biochemical reactions, as well as the nature of the electrical pulses
used by advanced biological organisms to transfer information between subsystems,
follow current theory.
Most biological materials are close to neutral in charge. This fact comes about
because in the temperature range within which water is liquid, oppositely charged
particles can stay bound together. Electric interactions dominate the force between
such charges, and it typically takes several electron volts of energy to pull a negative
charge from a positive one when they are initially separated by atomic distances. The
energy available by thermal collisions is about 1/25 eV. Life systems use electric
forces present in molecular and chemical interactions to do purposeful work by
pulling charges around.
Our everyday experience with electricity comes from the transfer of a very small
fraction of the charge from one body to another. The flux of one tenth of a trillionth
of a percent of your electrons traveling as a spark from your finger to a doorknob
can produce a painful searing of a nerve ending. (If the gap was half a centimeter,
the electric potential from finger to knob would have been about 15,000 V.) At
the microscopic level in biology, electric fields arise when charges are separated,
such as within molecules (giving them an “electric polarization”), by cell walls,
through biochemical reactions of molecules and ions, between ions in solutions,
and by ion pumps in cell walls. Some molecules, like water, have built-in electric
polarization. The strongly polarized water molecules make water a good solvent
for other polarized molecules and ionic salts. Other molecules become polarized by
being stressed in external electric fields (“induced electric polarization”). Charge
separation and transfer is often used in life systems to drive biochemical reactions.
Even so, electric forces in biosystems tend to be limited in range, because within
the protoplasm of our cells, excess charge on a molecule will attract ions of
the opposite charge, shielding the molecule from other long-range electric forces.
However, significant charge separation can be maintained across cell membranes.
Even so, the change in the electric potential across a resting nerve cell is only
about 0.07 V.
The strength of an electric field is not normally reported in newtons per coulomb,
but rather in volts per meter, in deference to the importance of energy. Energy is
exchanged whenever the action of an electric field causes a charge to moves over
some distance. If the field pushes the charge over some distance, the charge gains
energy taken from the agent producing the electric field. The energy gained by a
unit test charge is call the ‘electric potential’, V . Inversely, the electric field is