Question

what would happen if plasma membranehad not been selectively permeable

Answer 1

Your answer
If plasma membrane has not been selectively permeable then the enzymes which harms the plants may enter into cell and may destroy it..
If selectively permeable membrane is not present then the required material which plants need may also be sent out and the cell may die...
Absence of selectively plasma membrane leads that the cell organelles may also sent out...
Hope It will help you