Answer:
The cell membranes are made of lipids that do not mix with water.
Step-by-step explanation:
Cells in the body are made up of a plasma membrane which is made up of phospholipids that have hydrophilic heads that dissolve in water and hydrophobic tails that do not dissolve in water. The membrane is a bilayer wherein the hydrophilic heads faces the aqueous environment both inside and outside the cells while the hydrophobic tails faces each other and cluster up preventing solubility in water.
The attraction of the hydrophilic heads to the water inside and outside of the cell and clustering of the hydrophobic tails together and avoiding mixing with water keeps the cell membrane in place.