How do a phospholipid behave in water?

In water, phospholipids spontaneously arrange themselves into a bilayer due to their amphipathic nature; they have hydrophilic (water-attracting) heads that orient towards the water and hydrophobic (water-repelling) tails that face inward, away from the water. This arrangement forms the foundational structure of cell membranes, allowing for the formation of a semi-permeable barrier. Additionally, the bilayer's fluidity enables the movement of proteins and other molecules within the membrane, essential for various cellular functions.