  Biological cells are built up from many different constituents of varying
size and stiffness which all contribute to the cell's mechanical properties.
Despite this heterogeneity, in the analysis of experimental measurements such
as atomic force microscopy or microfluidic characterisation a strongly
simplified homogeneous cell is typically assumed and a single elastic modulus
is assigned to the entire cell. This ad-hoc simplification has so far mostly
been used without proper justification. Here, we use computer simulations to
show that indeed a heterogeneous cell can effectively be replaced by a
homogeneous equivalent cell with a volume averaged elastic modulus. To study
the validity of this approach, we investigate a hyperelastic cell with a
heterogeneous interior under compression as well as in shear and channel flow,
mimicking atomic force and microfluidic measurements, respectively. We find
that the homogeneous equivalent cell reproduces quantitatively the behavior of
its inhomogeneous counterpart, and that this equality is largely independent of
the stiffness or spatial distribution of the heterogeneity.
