Manipulate[GraphicsRow[{Plot[Evaluate[{R[t],X[t],P[t]}/.NDSolve[{R'[t]==-kf1*R[t]+kr1*X[t],X'[t]==kf1*R[t]-(kr1+kf2)*X[t]+kr2*P[t],P'[t]==kf2*X[t]-kr2*P[t],R[0]==10,X[0]==0,P[0]==0},{R,X,P},{t,0,5}]],{t,0,5},PlotRange->{0,10},AxesLabel->{t,"C"}],LogLinearPlot[Evaluate[{R'[t],X'[t],P'[t]}/.NDSolve[{R'[t]==-kf1*R[t]+kr1*X[t],X'[t]==kf1*R[t]-(kr1+kf2)*X[t]+kr2*P[t],P'[t]==kf2*X[t]-kr2*P[t],R[0]==10,X[0]==0,P[0]==0},{R,X,P},{t,0,5}]],{t,0.001,5},PlotRange->All,AxesLabel->{"t","d[C]/dt"}],LogPlot[Evaluate[{R[t]/X[t]}/.NDSolve[{R'[t]==-kf1*R[t]+kr1*X[t],X'[t]==kf1*R[t]-(kr1+kf2)*X[t]+kr2*P[t],P'[t]==kf2*X[t]-kr2*P[t],R[0]==10,X[0]==0,P[0]==0},{R,X,P},{t,0,5}]],{t,0.0,5},PlotRange->All,AxesLabel->{"t","C"}]},ImageSize->{1000,300}],{kf1,0.1,10},{kr1,0,10},{kf2,0.1,10},{kr2,0,10}]

JOSE

r1[t_,kf1_,kr1_]:=-kf1*R[t]+kr1*X[t];r2[t_,kf2_,kr2_]:=-kf2*X[t]+kr2*P[t];eqs[kf1_,kr1_,kf2_,kr2_]:={R'[t]==r1[t,kf1,kr1],X'[t]==-r1[t,kf1,kr1]+r2[t,kf2,kr2],P'[t]==-r2[t,kf2,kr2],R[0]==10,X[0]==0,P[0]==0};Manipulate[GraphicsRow[{Plot[Evaluate[{R[t],X[t],P[t]}/.NDSolve[eqs[kf1,kr1,kf2,kr2],{R,X,P},{t,0,5}]],{t,0,5},PlotRange->{0,10},AxesLabel->{t,"C"}],LogLinearPlot[Evaluate[{R'[t],X'[t],P'[t]}/.NDSolve[eqs[kf1,kr1,kf2,kr2],{R,X,P},{t,0,5}]],{t,0.001,5},PlotRange->All,AxesLabel->{"t","d[C]/dt"}],LogPlot[Evaluate[{R[t]/X[t]}/.NDSolve[eqs[kf1,kr1,kf2,kr2],{R,X,P},{t,0,5}]],{t,0.00,5},PlotRange->All,AxesLabel->{"t","C"}]},ImageSize->{1000,300}],{kf1,0.1,10},{kr1,0,10},{kf2,0.1,10},{kr2,0,10}]