  We discuss the influence of the 12C(alpha,gamma)16O$ reaction rate on the
central He burning of stars in the mass range 0.8-25 Msun, as well as its
effects on the explosive yields of a 25 Msun star of solar chemical
composition. We find that the central He burning is only marginally affected by
a change in this cross section within the currently accepted uncertainty range.
The only (important) quantity which varies significantly is the amount of C
left by the He burning. Since the C(alpha,gamma)16O is efficient in a
convective core, we have also analyzed the influence of the convective mixing
in determining the final C abundance left by the central He burning. Our main
finding is that the adopted mixing scheme does not influence the final C
abundance provided the outer border of the convective core remains essentially
fixed (in mass) when the central He abundance drops below about 0.1 dex by mass
fraction; vice versa, even a slight shift (in mass) of the border of the
convective core during the last part of the central He burning could
appreciably alter the final C abundance. Hence, we stress that it is wiser to
discuss the advanced evolutionary phases as a function of the C abundance left
by the He burning rather than as a function of the efficiency of the
12C(alpha,gamma)16O reaction rate. Only a better knowledge of this cross
section and/or the physics of the convective motions could help in removing the
degeneracy between these two components. We also prolonged the evolution of the
two 25 M_sun stellar models up to the core collapse and computed the final
explosive yields.
