Set Startup partition:

Any Macintosh partition created by the DriveManager can be set as the Macintosh startup volume.  By checking the box next to this option, the Macintosh will attempt to start up from the selected partition if and when it tries to start up from that partition’s drive.  However, this partition cannot be given a password.

NOTE:  You must make sure that the drive to which this partition belongs is the drive that the Macintosh will start up from.  See the User's Manual for information on setting a particular drive to be the startup device.