Answer: The hydrophilic tails are directed inward and the hydrophobic heads are directed outwards.
Explanation:
A phospholipid is made up of two ends a hydrophilic or water-loving end that is phosphate head and a hydrophobic tail that is made up of fatty acid tail. The arrangement of phospholipid in a bilayer structure allows the entry of oxygen, carbon dioxide, and lipids to pass through them via concentration gradient via simple diffusion.
Lipids are amphipathic molecules that compose the membrane. Membrane lipidic bilayers allow only the hydrophilic heads to interact with water inside and outside the cell, while hydrophobic tails remain in the interlayer space, away from water.
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Two lipidic layers compose the cell membrane. There are also proteins and glucans incrusted in between.
Since lipids are amphipathic molecules with hydrophilic heads -negatively charged phosphate group- and hydrophobic tails, they need to form two opposite layers.
Lipids are arranged with their hydrophilic polar heads facing the exterior and the interior of the cells in contact with water. Meanwhile, their hydrophobic tails are against each other, constituting the internal part of the membrane.
Membranes are fluid, meaning that lipids and proteins composing them can move laterally, transversally, or rotationally.
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