Final answer:
Lipids in cell membranes are organized into a bilayer structure with hydrophilic heads and hydrophobic tails. The bilayer acts as a barrier, allowing selective passage of substances and maintaining fluidity.
Step-by-step explanation:
The lipids in cell membranes are organized into a bilayer structure. The lipids, specifically phospholipids, have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The hydrophilic heads face the aqueous external and internal environments, while the hydrophobic tails are sandwiched between the hydrophilic heads, creating a barrier that prevents the free passage of molecules and ions.
The bilayer is important for membrane activities because it provides a flexible and selective barrier. It allows only certain substances to enter or exit the cell through the embedded protein channels, which can move specific ions and molecules across the membrane. The bilayer also helps maintain the fluidity of the cell membrane, allowing it to adapt to changes in the cell's environment and facilitate various cellular processes.