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Triglycerides have polar (charged) heads and non polar fatty acid tails so the charge on the molecule is unevenly distributed.

The polar head attracts water (which is also polar molecule due to unevenly charge distribution). The hydrophobic tails repel water as they are water insoluble. This causes the triglycerides to arrange themselves where polar heads surrounding water in the cytoplasm and the tails are pointed away.

They form spherical droplets rather than any other shapes because, a sphere is the most efficient shape to form in nature. An example of this is that bubbles are nearly always spherical.

Triglycerides form by condensation (dehydration) reactions between the hydroxyl (OH) groups of the glycerol and the carboxyl (COOH) group of three fatty acids.Triglycerides are esters being derived from an alcohol and a fat. Triglycerides are insoluble in water because they have no charge i.e. they have covalent bonds. This causes them to form droplets in the cytoplasm

The structure of phospholipids is based on the structure of triglycerides but the third hydroxyl group of the glycerol is linked to phosphoric acid which is often linked to a large polar group.The fatty acids which make up phospholipids have a consistent length of between 16 and 18 carbons. This allows them to form neat bilayers. Phospholipids are said to be amphipathic, having two very different sides to their nature.

because heads, water loving, are attracted to the water in the cytoplasm inside the cell and the watery fluids outside the cell 

Phospholipids forms bilayers because one end is soluble in water and other end is i soluble in water.

Triglycerides form droplets because of uneven distribution of charge within molecules.

Phospholipids are made up of one glycerol molecule attached to 2 fatty acid tails and 1 phosphate group. 

  • The fatty acid 'tails' are hydrophobic (repel water)
  • The phosphate 'head' is hydrophilic (attracts water)
  • Therefore, phospholipids are polar - there is an uneven distribution of charge.
  • Because one end of the phospholipid molecule is soluble in water and one end is not, when in water, the phospholipids position themselves so that their hydrophilic heads are close to the water and their hydrophobic tails are as far away from the water as possible --> resulting in the formation of a lipid bi-layer (two layers of phospholipids organised in 2 sheets). 

Triglycerides (one glycerol with 3 fatty acid tails) are not polar, meaning there is no uneven distribution of charge within the molecules. Therefore, they cannot form hydrogen bonds with water and therefore cannot dissolve in water:

  • They are hydrophobic i.e. they lack a water soluble part. 
  • Because they can't dissolve in water, they group together as fat droplets in the cytoplasm of the cell.
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