Final answer:
Microtubules grow by adding more tubulin subunits at the plus end and shrink by disassembling at the minus end.
Step-by-step explanation:
Microtubules require the addition of more tubulin subunits to grow. The growth of microtubules occurs at the plus end, which is fueled by GTP hydrolysis. By adding more tubulin subunits, microtubules can grow like adding additional links to a chain.
On the other hand, microtubules shrink by disassembling at the opposite end, known as the minus end. This disassembly is powered by changing the shape of cells or during cell division. Microtubules have polarities, meaning they have plus ends and minus ends, and can grow or shrink accordingly.