Final answer:
Phospholipids contain hydrophilic heads that face outwards and hydrophobic tails that face inwards, forming a structure called a phospholipid bilayer, which is essential for creating cell membranes that act as selective barriers.
Step-by-step explanation:
The group of lipids that will contain a barrier formed by hydrophilic heads that face outwards and hydrophobic tails that face inwards is known as phospholipids.
This structure is fundamental to cell membranes and is referred to as a phospholipid bilayer.
In water, phospholipids tend to spontaneously arrange themselves into a bilayer, with the hydrophobic tails shielded from water, creating the interior of the bilayer, while the hydrophilic heads interact with the water on either side of the bilayer.
This excellent ability to self-assemble into liposomes or micelles makes phospholipids essential for forming cell membranes, providing a dynamic, yet selective barrier from the surrounding environment.
Moreover, the fluidity of the bilayer is influenced by the type of fatty acids present in the phospholipids.
Saturated fatty acids pack tightly and make the bilayer more rigid, while unsaturated fatty acids with kinks lead to a looser arrangement and contribute to a more fluid bilayer.