Phospholipids

Lipids are a class of macromolecules that are vital to life and have special properties that aid in the structure, maintenance, and metabolic activities of living organisms. Their exact origin has not yet been discovered, however it is clear that lipids were formed by straightforward processes in the environment, and over time they eventually developed into more complex structures (like the many varieties of phospholipids) that form membrane components of cells. Because they can form membranes, lipids must have been to be one of the first processes that started life to occur because cells could never survive without a protective barrier protecting and regulating their internal components from its respective environment. The most important properties of lipids are their polar nature, making them amphipathic (meaning they have hydrophilic and hydrophobic parts). Phospholipids are macromolecules that are made up of a phosphate head group, glycerol backbone, and 2 chains of fatty acid tails. Below is a photo showing their structure and the variety of ways they can be represented:

https://sites.gsu.edu/biol2107teamnucleus_maxwell/wp-admin/media-upload.php?post_id=33&type=image&TB_iframe=1
(Photo retrieved from Biology: How life works, 2nd edition)

Their amphipathic nature is what gives phospholipids their ability to form membranes. The polar head groups are hydrophilic and make them “water loving”, and their hydrophobic tails are hydrophobic, or “water fearing”. This becomes apparent when enough phospholipids are added to an aqueous solution. The Polar heads will attach to each other by Van der waals forces (the association between molecules by their slight charges), and the fatty acid tails would will line up side-by-side. Because the polar tails want to be separated from water, the polar heads will eventually form a protective barrier to the aqueous environment. The varying bulk of the polar heads will determine what kind of membrane will form. They can make spherical micelles that have the nonpolar tails oriented on the inside, a fluid bilayer that has the tails sandwiched inside 2 layers of polar heads, and spherical vesicles that have a layer of polar heads both inside and outside of the cell.
The fact that these lipids spontaneously come together in the previously mentioned fashion gives them an ability to repair itself when the phospholipid bilayer is broken. If phospholipids from the environment or made from cellular processes are present, they will be added to the membrane until the damage is repaired. This along with its amphipathic nature makes them very effective membranes. Phospholipids can also associate with cholesterol, proteins, and other slightly charged molecules needed for metabolism to become selectively permeable. This is shown in all cell membranes because molecules needed for energy consumption and regulation must be able to enter and exit the cell as needed to maintain a proper electrochemical gradient, PH, and solute concentration if the cell is to survive.

References
Biology: How life works (2nd ed.). (2017). In B. A. Berry Andrew, Biology: How life works (2nd ed.) (p. CH 5.1). McGraw Hill, NY: W. H. Freeman. Retrieved from http://www.macmillanhighered.com/launchpad/morris2e/4909413#/ebook/item/MODULE_bsi__F4951CED__2971__4486__BC4F__E109B2EE87D4/bsi__2ED633B9__F1E8__4C6C__82AA__0633C0C9F474?mode=Preview&toc=syllabusfilter&readOnly=False&renderIn=fne
Openstax. (2013). Biology. In Openstax, Biology (p. Ch1.1). Houston, TX: Rice University.
Suetsugu, S. K. (2014). Dynamic shaping of cellular membranes by phospholipids and membrane-deforming proteins. Physiological Reviews, 94(4), 1219-1248. Retrieved April 3, 2017, from http://physrev.physiology.org/content/94/4/1219