a. Controlling the exchange of substances between cytoplasm and its environment.
b. As a receptor of stimulation, such as hormone and other chemical matters that come from environmentor other parts within cell itself
c. As a cell protector to keep the content of cell stay within.
d. Controlling substances that will enter/exist the cytoplasm.
In plant cell and prokaryotic cell, the cell membrane changes into stiff structure called cell wall that functions as protector and supporter. The organelle is formed from protoplasm activities.
Between wall of two nearby cells, there is middle lamelle. Between two nearby cell, there is also pore. Throught the pores, plasma of two neighbor cell is connected by plasma strands (plasmodesma) Plasmodesma is predicted to have roles in facilitating substance movement and delivering impuls among cells.