There are MANY great functions already built into MATLAB to create and analyze system and to plot their responses.
Use the 'help' command to explore the possibilities. For instance:
help bode
Some ther useful commands include:
step
tf
tfdata
ss
ssdata
zpk
zpkdata
pzmap
...but there are many more.
Often, the end of brief function description you get from the help command will list related functions (about which you can then also request 'help' in MATLAB).