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[foh-tuh-peer-ee-uh-diz-uh m] /ˌfoʊ təˈpɪər i əˌdɪz əm/
noun, Biology.
the response, as affecting growth or reproduction, of an organism to the length of exposure to light in a 24-hour period.
Also called photoperiodicity
[foh-toh-peer-ee-uh-dis-i-tee] /ˌfoʊ toʊˌpɪər i əˈdɪs ɪ ti/ (Show IPA)
Origin of photoperiodism
First recorded in 1915-20; photoperiod + -ism Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for photoperiodism


the response of plants and animals by behaviour, growth, etc, to photoperiods
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for photoperiodism

1920, from photoperiod (1920, from photo- + period) + -ism.

Online Etymology Dictionary, © 2010 Douglas Harper
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photoperiodism in Medicine

photoperiodism pho·to·pe·ri·od·ism (fō'tō-pĭr'ē-ə-dĭz'əm) or pho·to·pe·ri·o·dic·i·ty (-pĭr'ē-ə-dĭs'ĭ-tē)
The response of an organism to changes in its photoperiod, especially as indicated by vital processes.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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photoperiodism in Science
photoperiodism (fō'tō-pîr'ē-ə-dĭz'əm) also photoperiodicity
The response of an organism to changes in its photoperiod, especially as indicated by vital processes. For example, many plants exhibit photoperiodism by flowering only after being exposed to a set amount of daylight, as by requiring either a long or short day to flower. Plant growth, seed germination, and fruiting are also affected by day length. Photoperiodic responses in plants are regulated by special pigments known as phytochromes. In animals, migration, mating, amount of sleep, and other behaviors are also photoperiodic. In many animals, photoperiodism is regulated by the hormone melatonin.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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