Growth rate and effective density for the tearing mode with wavelength = 0.4 Mm, the fastest growing mode for η₀ = 8 Ωm, and densities at z = 3.5 Mm. The growth rate obtained in the MHD approximation is shown by a solid black line. The growth rates in the two-fluid approach are located on this line, depending on the value of the collisional parameter α. Several values of α are considered, as indicated in the legend in which we also show the (ρ, γ) coordinates of the points in brackets.