The --chunk --partition and --range options compile different work agenda lists for the supervisor. The --range option creates a list of frames, the --partition and --chunk creates lists of ranges (--partition divides a range into a specified number of ranges, the --chunk divides a range into a list of ranges each with a specified size).
When the Worker executes the backend, it goes into a loop of requests a work agenda item from the Supervisor, which would be in the form of a frame or a frame range, then executing it. The QB_FRAME_NUMBER is a macro that it uses to substitute a single frame into the submitted command line, and the QB_FRAME_START and QB_FRAME_END are macros used to substitute the first and last frames of a range into the command line.