Final answer:
The phospholipids in a cell membrane have hydrophilic heads facing the water-based inside and outside of the cell, while the hydrophobic tails face each other inside the membrane, forming a phospholipid bilayer critical for cellular integrity.
Step-by-step explanation:
The phospholipids of a cellular membrane have distinct orientations based on their affinity to water. The hydrophilic ends, which are the phosphate groups, face both the inside and outside of the cell where water is present – thus, these ends are also called 'heads'. Conversely, the hydrophobic ends, known as the fatty acid tails, face each other on the inside of the membrane, avoiding water, which is why these ends are referred to as 'tails'.
Cells are wrapped in a membrane that ensures structural integrity in a water-based environment because of the phospholipid bilayer. This bilayer's formation is due to the polar, water-attracting nature of the heads and the non-polar, water-repelling nature of the tails, creating a stable barrier that is also fluid, allowing the necessary flexibility for various cellular processes.