Zoid

In botany, a zoid or zoïd is a reproductive cell that possesses one or more flagella, and is capable of independent movement. Zoid can refer to either an asexually reproductive spore or a sexually reproductive gamete. In sexually reproductive gametes, zoids can be either male or female depending on the species. For example, some brown alga (Phaeophyceae) reproduce by producing multi-flagellated male and female gametes that recombine to form the diploid sporangia. Zoids are primarily found in some protists, diatoms, green alga, brown alga, non-vascular plants, and a few vascular plants (ferns, cycads, and Ginkgo biloba). The most common classification group that produces zoids is the heterokonts or stramenopiles. These include green alga, brown alga, oomycetes, and some protists. The term is generally not used to describe motile, flagellated sperm found in animals. Zoid is also commonly confused for zooid which is a single organism that is part of a colonial animal.

==Diversity of zoids== A zoid contains one or more flagella for motility. In the various species that produce zoids, there is a high level of diversity in the number of flagella produced. The heterokonts generally produce zoids with 2 flagella, while the Ginkgo biloba produce zoids with tens of thousands of flagella. The position of the flagella and the arrangement of the microtubules varies among species as well. The following sections will briefly outline general characteristics of the zoids found in each subset as well as provide specific examples.