Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer. The fatty acid tails of phospholipids face inside, away from water, whereas the phosphate heads face the outward aqueous side.
Since the heads face outward, one layer is exposed to the interior of the cell and one layer is exposed to the exterior. As the phosphate groups are polar and hydrophilic, they are attracted to water in the intracellular fluid. As a result, there are two distinct aqueous compartments on each side of the membrane.
This separation is essential for many biological functions, including cell communication and metabolism.
Biological membranes remain fluid because of the unsaturated hydrophobic tails, which prevent phospholipid molecules from packing together and forming a solid. If a drop of phospholipids are placed in water, the phospholipids spontaneously forms a structure known as a micelle, with their hydrophilic heads oriented toward the water.
Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solution. Ben Franklin Stilled the Waves. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable.
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This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings. Scitable Chat. The plasma membrane is composed mainly of phospholipids, which consist of fatty acids and alcohol.
The phospholipids in the plasma membrane are arranged in two layers, called a phospholipid bilayer. As shown in Figure below , each phospholipid molecule has a head and two tails. The water -hating tails are on the interior of the membrane, whereas the water-loving heads point outwards, toward either the cytoplasm or the fluid that surrounds the cell. Molecules that are hydrophobic can easily pass through the plasma membrane, if they are small enough, because they are water-hating like the interior of the membrane.
Molecules that are hydrophilic, on the other hand, cannot pass through the plasma membrane—at least not without help—because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane. Phospholipid Bilayer. The phospholipid bilayer consists of two layers of phospholipids, with a hydrophobic, or water-hating, interior and a hydrophilic, or water-loving, exterior. The hydrophilic polar head group and hydrophobic tails fatty acid chains are depicted in the single phospholipid molecule.
The polar head group and fatty acid chains are attached by a 3-carbon glycerol unit.
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