Terrestial Exposure Pathways project using MATLAB, HELP!

[ssbnsailor]

I am currently working on a graduate project for a hazardous waste and radiological assessment class and need to use MATLAB for solving coupled ODEs. This may be basic for some people, but I have never used MATLAB so I am trying to self-teach myself. Below is my m-file, it keeps telling me that input argument 'x' is undefined. I am not sure what I'm doing wrong and pounding my head against my desk is giving me a headache. I have rooted through the technical references and can't find an answer. All I want to do is solve the equations and have it spit out the equation for the various compartments in my model (i.e. x1=...,x2=...). I appreciate any help.

growing season.m:
function xdot=conc(t,x)
%CONC terrestial compartment concentration equation
% xdot=conc(t,x)
% xdot(1)=delta1*v*x(0)+lamba12*x(2)-(lamba+lamba21+VhYc/Ac)*x(1)
% xdot(2)=delta2*v*x(0)+lamba21*x(1)-(lamba+lamba12+lamba52+lamba62)*x(2)
% xdot(3)=delta3*v*x(0)+lamba34*x(4)-(lamba+lamba43+VcYg/Ag)*x(3)
% xdot(4)=delta4*v*x(0)+lamba43*x(3)-(lamba+lamba34+lamba64)*x(4)
% xdot(5)=lamba52*x(2)-(lamba+VhYc/Ac)*x(5)
% xdot(6)=lamba62*x(2)+lamba64*x(4)-lamba*x(6)
% xdot(7)=lamba73*x(3)-(lamba+lambab)*x(7)
% xdot(8)=lamba83*x(3)-(lamba-lambam)*x(8)
% xdot(9)=Ea*x(1)+Ua*x(5)+Ba*x(7)+Ma*x(8)+a12*x(10)-(lamba+a31)*x(9)
%GI TRACT intake
% xdot(10)=deltaa*Ia*x(0)-(lamba+a12+a32)*x(10)
%LUNG intake
% xdot(11)=a31*x(9)+a32*x(10)+a34*x(12)-(lamba+a43+a53+a63)*x(11)
%Cellular fluids
% xdot(12)=a43*x(11)-(lamba+a34+a54)*x(12)
%Soft Tissue
%CONSTANTS ARE BELOW
%deltaa = 0.63
%Ia = 23
%Ea = 0.0049
%Ua = 1.9
%Ba = 0.28
%Ma = 0.36
%lamba12 = 6*10^-9
%lamba21 = 0.08
%lamba52 = 6*10^-9
%lamba62 = 10^-4
%lamba34 = 8*10^-3
%lamba43 = 0.08
%lamba64 = 10^-4
%lamba = 6.34*10^-5
%VhYc = 1.25
%Ag = 10^4
%VcVg = 100
%Ac = 10^3
%lambab = 0.00381
%lambam = 2
%a12 = 0.88
%a31 = 17
%a32 = 1.9
%a43 = 3.1
%a53 = 0
%a63 = 0.33
%a34 = 0
%a54 = 0.063
%delta1 = 0.90
%delta2 = 0.10
%delta3 = 0.90
%delta4 = 0.10
%v = 691.2
%lamba73 = 0.004
%lamba83 = 0.8
%x(0) = 0.00000027 airborne concentration
%airborne concentration will be ac in equations vice x(0)
%All of the constants are for the growing season of 0-120 days

deltaa = 0.63;
Ia = 23;
Ea = 0.0049;
Ua = 1.9;
Ba = 0.28;
Ma = 0.36;
lamba12 = 6*10^-9;
lamba21 = 0.08;
lamba52 = 6*10^-9;
lamba62 = 10^-4;
lamba34 = 8*10^-3;
lamba43 = 0.08;
lamba64 = 10^-4;
lamba = 6.34*10^-5;
VhYc = 1.25;
Ag = 10^4;
VcVg = 100;
Ac = 10^3;
lambab = 0.00381;
lambam = 2;
a12 = 0.88;
a31 = 17;
a32 = 1.9;
a43 = 3.1;
a53 = 0;
a63 = 0.33;
a34 = 0;
a54 = 0.063;
delta1 = 0.90;
delta2 = 0.10;
delta3 = 0.90;
delta4 = 0.10;
v = 691.2;
lamba73 = 0.004;
lamba83 = 0.8;
ac = 0.00000027;
xdot(1)=delta1*v*ac+lamba12*x(2)-(lamba+lamba21+VhYc/Ac)*x(1);
xdot(2)=delta2*v*ac+lamba21*x(1)-(lamba+lamba12+lamba52+lamba62)*x(2);
xdot(3)=delta3*v*ac+lamba34*x(4)-(lamba+lamba43+VcYg/Ag)*x(3);
xdot(4)=delta4*v*ac+lamba43*x(3)-(lamba+lamba34+lamba64)*x(4);
xdot(5)=lamba52*x(2)-(lamba+VhYc/Ac)*x(5);
xdot(6)=lamba62*x(2)+lamba64*x(4)-lamba*x(6);
xdot(7)=lamba73*x(3)-(lamba+lambab)*x(7);
xdot(8)=lamba83*x(3)-(lamba-lambam)*x(8);
xdot(9)=Ea*x(1)+Ua*x(5)+Ba*x(7)+Ma*x(8)+a12*x(10)-(lamba+a31)*x(9);
xdot(10)=deltaa*Ia*x(0)-(lamba+a12+a32)*x(10);
xdot(11)=a31*x(9)+a32*x(10)+a34*x(12)-(lamba+a43+a53+a63)*x(11);
xdot(12)=a43*x(11)-(lamba+a34+a54)*x(12);