Z lines: The borders of a sarcomere.
Zero population growth: A period os stability in population size, when the per capita birth rate and death rate are equal.
Zona pellucida: The extracellular matrix of a mammalian egg.
Zone of cell division: The zone of primary growth in roots consisting of the root apical meristem and its derivatives. New root cells are produce in this region.
Zone of elongation: The zone of primary growth in roots where new cells elongate sometimes up to ten times their original length.
Zone of maturation: The zone of primary growth in roots where cells complete their differentiation and become functionally mature.
Zone of polarizing activity (ZPA): A limb-bud organizer region consisting of a block of mesoderm located where the posterior side of the bud is attached to the body.
Zoospore: Flagellated spore occurring in chytrid fungi.
Zosterophyll: A type of early vascular plant that carried spores laterally along the stem.
Zygomycete: Member of a fungal phylum Zygomycota, characterized by forming a sturdy structure called zygosporangium during sexual reproduction.
Zygosporangium: In zygomycete fugi, a sturdy multinucleate structure in which karyogamy and meiosis occur.
Zygote: Diploid, one-cell totipotent embryo formed at fertilization between the egg and the sperm. The zygote represents the earliest developmental stage of an embryo.