1 : of, relating to, or having only two experimental alternatives (such as dead or alive, all or none)
2 : of or relating to a quantum or to quanta (as of energy or a neurotransmitter)
Did You Know?
In Latin, quantum is the neuter form of quantus, meaning "how much?" Both of these forms played a role in the development of quantal. The first sense of quantal, used in scientific experimentation to refer to cases in which only one of two possible results occurs, derived from quanti, the plural of quantus. (Quantus is also an ancestor of our noun quantity.) The second sense of quantal is more directly related to Latin quantum and the English noun quantum, which refers to the smallest possible unit of a form of energy (such as light).
"Many bioassays are based on quantal responses: Challenge assays record whether the subjects are dead or alive (or moribund or not moribund) at the end of the assay; seed-germination assays record whether seeds germinate by the end of the assay." — Ann Yellowlees et al., BioScience, June 2013
"Suppose you shake a crib with a sleeping baby. If you shake it hard, the baby always wakes up. However, if you shake it gently, the baby might wake up. The waking up itself is a quantal event—the baby is either awake or asleep—but the probability of this happening depends on how hard you rock." — Sönke Johnsen, The Optics of Life: A Biologist's Guide to Light in Nature, 2012
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