  Possible origins of the experimentally observed beat-like signal in elastic
light backscattering from an epithelial biological cell are identified. The
source of the beat-like signal is most likely the cellular nucleus, which is a
spheroidal particle with an optically sharp edge, low relative index of
refraction, and a size parameter in the resonant range; another possible source
is an agglomeration of cell organelles of a similar size. Using Mie theory
computer simulations for a dielectric sphere with biological nucleus-like
parameters, we have shown that backscattering as a function of size parameter
has a beat-like pattern. The high frequency periodic oscillation is the single
scattering contribution, while multiple scattering events give slowly varying
oscillatory contributions. With increasing contrast, the backscattering signal
changes from a pure sinusoid to that of a beat signal. The beat-like pattern in
scattering from a low contrast particle does not depend on any particular
features of the sphere; a similar pattern is observable in scattering from
star-like non-spherical objects with a sharp optical contrast and smooth shape;
in this case, the high frequency of oscillations depends on the object
orientation relative to incident light
