In 1935, Davson and Danielli suggested that 40 percent of the lipid molecules are arranged in a 'lipid bilayer'. Each phospholipid molecule consists of a glycerol molecule linked to two long chain fatty acids and a phosphate group or phosphate head. The 'lipid bilayer' forms due to the hydrophobic and the hydrophilic nature of the phospholipid. The polar head or phosphate group is 'hydrophilic' or 'water loving' and the two fatty acid tails are hydrophobic, or 'water hating'. The bilayer is therefore arranged in order for the fatty acids to exclude as much water as possible their structure.

With improvements in technology (improvements in electron microscopy), a more detailed structure of the cell plasma membrane was laid out. The two scientists, in 1972, by the name of Singer and Nicolson, suggested that the membrane is a fluid structure and is always moving. They put forward the idea of the ' flui

There are many internal bound organelles that contain a double membrane around them. One example is the nucleus. The main function of this membrane is to act as a barrier between the reactions occurring in the nucleus compared to the reactions occurring in the cytoplasm of the cell. There are large pores, around the size of 50 to 80 nm in diameter that are found on the nuclear membrane. This makes is partially permeable, in which it allows substances such as RNA to pass out of the nucleus in order for it to synthesise proteins on the endoplasmic reticulum. Mitochondria also pocess a double membrane structure. In this organelle, the outer membrane plays an important protective, selective transport role. The inner membrane is enfolded into shelf like projections called cristae (singular: Crista). This gives a large surface area for the enzymes associated with the synthesis of ATP to work on.

The main functions of the membrane proteins is to act as receptor sites in order to transport substances in and out of the cell by facilitated diffusion. The membrane proteins are also used for 'active transport' mechanisms, in where they are called 'pumps'. A famous example is the sodium and potassium pump. This protein is called the sodium

Some common words found in the essay are:
Substances CO, Singer Nicolson, Davson Danielli, , ATP Overall, cell surface membrane, cell surface, surface membrane, lipid molecules, main function, plasma membrane, lipid bilayer, chemical reactions cell, reactions cell, chemical reactions, sodium potassium, environment cell, percent lipid molecules, pass lipid bilayer, 40 percent lipid,
Approximate Word count = 833
Approximate Pages = 3 (250 words per page double spaced)