According to fluid mosaic model given by Singer and Nicholson (1972), plasma membrane consists of a continuous bilayer of phospholipid molecules, in which globular proteins are embedded. This arrangement corresponds to icebergs (proteins) floating in a sea of phospholipids. Proteins stay in the membrane because they have regions of hydrophobic amino acids which interact with fatty acid tails to exclude water. Rest of the molecule is hydrophilic, which faces into or outward, both of which are aqueous environment.