Explanation: A cell membrane is a phospholipid bilayer with proteins embedded in it. The fatty acyl chains of the phospholipids are non polar and hydrophobic while the phosphate groups are polar and hydrophilic. The hydrophobic regions of the phospholipids interact with each by facing each other, forming a bilayer with a fluid interior. The polar head groups face outward interacting with the external environment of the cell. Proteins are embedded in this bilayer and they float in this sea of phospholipids. Proteins anchored to the membrane through interactions between the hydrophobic regions of the phospholipids and the amino acid side chains of the proteins. These lipids and proteins swim laterally in each face of the bilayer but movement from one face of the bilayer to another is restricted.
Epithelial cells are mainly used for protection; in the urinary tract, these tissue cells are used to protect the bladder from toxic urine. The tissue can also expand to hold larger quantities of urine.
