Solution: The physical barrier that prevents protoplast fusion is the cell wall. With the help of the enzymes cellulase and pectinase, the cell wall, which is made up of cellulose and pectin, is dissolved. The fusing of protoplast is then accomplished through electrical or chemical means. The cell wall is the most and only physical barrier of a cell in the protoplast. This physical barrier is overcome by its breakdown. The breakdown of the cell wall is done by digesting the cell wall.