Final answer:
Growing microtubule ends are stabilized by the addition of tubulin dimers, which are required for their structural and functional roles within the cell.
Step-by-step explanation:
Growing microtubule ends are normally stabilized by the addition of tubulin dimers, specifically alpha-tubulin and beta-tubulin, to the plus end (or +end) of the microtubule. This process is energy-dependent and fueled by the hydrolysis of GTP. Microtubules provide structural support to cells, create tracks for vesicle movement, and are essential during cell division for the correct separation of chromosomes. They have the inherent ability to quickly assemble and disassemble, a property that is crucial for their dynamic functions in the cell.