Cell Membrane
Source: http://www.ibiblio.org/virtualcell/textbook/chapter3/cms1.htm
Plants and animals have what is called a cell membrane. The cell membrane is a flexible lipid bilayer. That is located on the outside of the cell. A lipid bilayer, as you can guess is a lipid. It is made up of a hydrophiliac polar head, which is known as "water loving", which is the yellow round shape. They also consist of a hydrophobic tail which is non-polar and is known as "water fearing", which are the two blue lines in the picture. The hydrophiliac heads and hydrophobic tails are arranged in a way that the tails are buried together and the heads are left exposed. Cell membranes are very unique for this reason, another reason they are really unique is because of the proteins that are on the surface. These proteins have many different functions such as, surface receptors, enzymes, surface antigens, and transporters. The main purpose of the cell membrane is to allow nutrition's and other materials in and to allow the disposal of the wastes they produce. The cell membrane is said to be "selectively permeable" because some substances can pass easily through it and some cannot pass through at all, and the cell membrane controls this. Below is a picture of of a lipid bilayer.
Cell Wall
Source: http://library.thinkquest.org/C004535/cell_wall.html
Outside of the cell membrane in only plants you will find the cell wall. The cell wall provides the main difference between plant cells and other Eukayotic cells. The cell wall is rigid and can be up to many micrometers in thickness. Even though it is rigid chemical signals and cellular excretions can get through it. It is composed of proteins, cellulose and polysaccarides. As you can see in the picture to the right there are three different layers of the cell wall. The first is the primary cell wall. The primary cell wall is thin and not very rigid, because it's like this it allows the cells to grow. The second layer of a cell wall is called the secondary cell wall. This is when the cell is fully grown. Sometimes it retains its primary wall and just thickens but other times it may deposit new layers of a different material. The cell wall interacts with it's neighbors to create a bound plant structure.