zeitgebers: are external cues that help maintain circadian rhythms by synchronising the activity of the bodys organs and glands.

Zeitgeist: refers to the ideas, trends and values that are dominant in a culture at a particular point in history.

zone of proximal development: the distance between a child's current abilities (when working unaided) and their potential abilities or what are able to achieve under expert guidance.

zygote: a fertilised cell that is produced after a sperm fertilises an egg.