Problems with Function handle

I'm trying to imitate a mathematical model with differential equations, but I can not make it work. I need to obtain the graph that I show in the image and the model that I try to make is example 3.2 of the PDF.

Moments ago he showed me an unidentical but similar graphic, now he does not give me anything.

The function:

function dydx = fff (x,y)
Kga=1*10^-5;

global Kh0;
global Kh1;

Ksr=1;



Vga=Kga*Ra*Gaby;
Vhi=Khi*Gagtp;
Vsr=Ksr*Gby*Gagdp;

dGabydx = -Vga-Vsr;
dGagtpdx = Vga-Vh0-Vhi;
dydx = [dGabydx dGagtpdx]';

The scrypt:

global Kh0;
global Kh1;
Kh0=0;
Kh1=0;

[x,y]= ode45(dydx,[0,2],[.1 .1]);
plot(x,y);

xlabel('tiempo (h)')
ylabel('biomasa')