Depletion region in JFET transistor?
Yes it is - the depletion will be wider at the drain because it is connected to the positive of the battery whereas the source is at a voltage closer to that on the gate. As the gate gets more negative the depletion region will grow and eventually the device will be deemed to be "cut-off" and exhibit only low leakage currents from drain to source. This is an N channel JFET. P channel JFETs operate the same but with both batteries reversed. Having said that some N channel JFETs will operate "about" the same when D and S are reversed in polarity - these are sometimes used as voltage controlled resistors.