Plasma Membrane
Each cell is surrounded by a cell membrane or plasma membrane. In a pant cell, it lies to the inner side of the cell wall. It forms the outer boundary of the cytoplasm. plasma Membrane has a trilaminar structure.
The plasma membrane consists of two layers of lipid molecules with  layer of protein molecules on either side. 
. It is selectively permeable.
. It bounds semi-fluid content of the cells.
. It protects the inner contents and helps in maintaining the internal   environment of the cell.

Nucleus is a small, spherical or oval structure located somewhere in the centre. It was discovered by Robert Brown in 1831. the nucleus is composed of Nuclear membrane, Nucleoplasm, nucleolus and chromatin network.
Nucleus regulates various life processes of the cell. It plays an Important role in cell division.

Cytoplasm consists of all the parts of the cell excluding nucleus. It occupies the major part of the cell. it is a semi-solid substance which is colourless, viscous and partly transparent. water is the main component (upto 90%) of cytoplasm. many chemical reactions takes place in it. a number of cell organeles and nonliving cell inclutions are found floating in cytoplasm.

hope it helps.. :)
plzzzz mark it as the best ^^

1 4 1
Plasma membrane 
the content of a cell is enclosed by the plasma acts as a barier and helps the substances inside a cell to remain con provides an outer membrane to the is also known as semi permeable membrane.

the nucleus is commonly seen as aspherical structure surrounded by a double membrane called nuclear envolpoe. it controls the activity of the cell by determining what proteins are stores the genetic information.

cytoplasm is a jelly-like substance, is made up of water and few dissolved helps to keep the cell organells dynamic and in motion.