  The radical pair mechanism is a leading hypothesis in animal magnetic
navigation. This mechanism associates the magnetic sense with the visual
system, the radical pairs in cryptochromes of the eye retina being specialized
magnetic receptors that modulate rhodopsin-mediated photoreception. There are
also nonspecific magnetic effects in biology, which occur mostly by chance and
originate from the interaction of weak magnetic fields with the magnetic
moments dispersed all over the organism at the microscopic level. The radical
pair mechanism cannot explain this type of response for many reasons. We have
previously shown that the above interaction has a finite probability of
resulting in an observable. Here, we develop our physical model of nonspecific
magnetic effects for the case of magnetic moments located in rotating
molecules. We generalize the results of recent experiments on gene expression
in plants in a constant magnetic field, and show that the precession of the
magnetic moments that reside on rotating molecules can be slowed relative to
the immediate biophysical structures. In quantum mechanical language, the
crossing of the quantum levels of magnetic moments conjointly with molecular
rotations explain nonspecific magnetic effects and leads to magnetic
field-dependences that are in good agreement with the experiment.
