What is the most significant chemical difference between triacylglycerols and glycerophospholipids that leads to their different functions?

Triacylglycerols (triglycerides) are non-polar or hydrophobic molecules

Glycerophospholipids (phosphoglycerides) are polar or hydrophilic

Explanation:

Triacylglycerides (TGs) are esters synthesized by the esterification of three molecules of glycerol and fatty acid, and this is essentially by the replacement of the three hydroxyl groups on glycerol with three fatty acids. This removes the hydrophilic property from the glycerol molecule hence TGs are only soluble in non-polar solvents like alcohol and benzene, and TGs are therefore the storage forms of fats in adipose tissues.

Glycerophospholipids are formed by the addition of two hydrophobic fatty acid groups and one phosphoric acid (phosphate group) to glycerol (alcohol) leaving a hydrophilic head (phosphate end) and a hydrophobic tail (fatty acid ends). This amphipathic property of this molecule makes it a suitable molecule for membrane structures, especially of cells (lipid bi-layer), with an arrangement where the hydrophilic side interacts with the aqueous environment, while the hydrophobic side makes contact with the non-aqueous environment.