Final answer:
The remarkable aspect of Ulva's spore and gametes is that they are isogamous reproductive cells, where gametes do not show sexual dimorphism. Additionally, Ulva exhibits an isomorphic alternation of generations, where both the gametophyte and sporophyte stages are morphologically similar.
Step-by-step explanation:
What is remarkable about the spore and gametes of the Ulva is that they represent isogamous reproductive cells. This means that the gametes, or sex cells, of the Ulva do not show any sexual dimorphism and appear identical, which is quite different from the common case where gametes are distinctly different as eggs and sperm. Additionally, the life cycle of Ulva is characterized by an isomorphic alternation of generations, where the multicellular haploid gametophyte and the multicellular diploid sporophyte look the same, making it difficult to distinguish between the two stages without genetic analysis.
While Ulva reproduces sexually via isogamous gametes, which fuse during fertilization, it also reproduces asexually through the dispersal of spores. The haploid spores and the diploid zygotes both demonstrate 'developmental potential' and can grow into full organisms, exhibiting a unique life cycle among algae.