Final answer:
In Ulothrix, starch is depleted when gametes are formed as it is used to provide energy and materials for gamete development.
Step-by-step explanation:
When gametes are formed in Ulothrix, starch is depleted. Starch is the storage form of glucose, which is the product of photosynthesis in plants and algal species like Ulothrix. During gametogenesis, the energy and carbon skeletons stored in starch are utilized for the development and maturation of gametes, leading to a reduction in starch reserves within the cells.