A new class of finite difference schemes is constructed for Fisher partial differential
equation i.e. the reaction-diffusion equation with stiff source term: αu(1 - u). These
schemes have the properties that they reduce to high fidelity algorithms in the diffusion
free case namely in which the numerical solutions preserve the properties inherent in the
exact solutions for arbitrary time step-size and reaction coefficient α > 0, and all non
physical spurious solutions including bifurcations and chaos that normally appear in the
standard discrete models of Fisher partial differential equation will not occur. The implicit
schemes so developed obtain the numerical solutions by solving a single linear algebraic
system at each step. The boundness and asymptotic behaviour of numerical solutions
obtained by all these schemes are given. The approach constructing the above schemes
can be extended to reaction-diffusion equations with other stiff source terms.