The most structurally diverse collection of organisms is the kingdom Protista. Most protists are unicellular, microscopic organisms, but a few are complex and multicellular. Protists are also the most diverse in terms of their life cycles, which can involve asexual or sexual reproduction. Composed of metabolically diverse organisms, the kingdom Protista contains the ancestral life-forms that gave rise to the three kingdoms of multicellular organisms¾the fungi, the plants, and the animals. Amoebas, members of …showed first 75 words of 585 total…

…showed last 75 words of 585 total…a unique arrangement of microtubules and other organelles clustered at one end of the cell. Sporozoans have complex life cycles that involve both asexual and sexual reproduction. Sexual reproduction involves the fertilization of a large female gamete by a small, flagellated male gamete. The zygote that results soon becomes a thick-walled cyst called an oocyte, which is highly resistant to drought and other unfavorable environmental conditions. The best known sporozoan is the malaria-causing parasite Plasmodium.