Final answer:
The movement of phospholipids in the plasma membrane gives rise to the fluid part of the fluid mosaic model. Phospholipids can form micelles, where the hydrophilic heads face the outside and the fatty acids face the interior. The lateral movement of phospholipids allows the membrane to remain fluid.
Step-by-step explanation:
The movement of phospholipids in the plasma membrane gives rise to the fluid part of the fluid mosaic model. Phospholipids are responsible for the dynamic nature of the membrane. When placed in water, phospholipids spontaneously form structures called micelles, where the hydrophilic phosphate heads face the outside and the fatty acids face the interior. These phospholipids can move laterally, allowing the membrane to remain fluid and flexible.