  The present paper is devoted to the study of the maximum number of limit
cycles bifurcated from the periodic orbits of the quadratic isochronous center
$\dot{x}=-y+\frac{16}{3}x^{2}-\frac{4}{3}y^{2},\dot{y}=x+\frac{8}{3}xy$ by the
averaging method of first order, when it is perturbed inside a class of
discontinuous quadratic polynomial differential systems. The \emph{Chebyshev
criterion} is used to show that this maximum number is 5 and can be realizable.
The result and that in paper \cite{LC} completely answer the questions left in
the paper \cite{LM}.
