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Orientation in time

as part of AS91603 NCEA L3 Biology

TermDefinition
actogram An activity / time graph for an organism.
biological clock An internal timing system in organisms.
circa- Means ‘about / approximately’. ONLY used to describe rhythms occurring in constant environmental (free-running) conditions.
circa-annual A rhythm of about one year occurring in constant environmental (free-running) conditions.
circadian A rhythm of about 24 hours occurring in constant environmental (free-running) conditions.
circa-lunar A rhythm of about one month occurring in constant environmental (free-running) conditions.
circa-tidal A rhythm of about 12.5 hours occurring in constant environmental (free-running) conditions.
crepuscular Most active at dawn and dusk.
critical day length The photoperiod above which long-day plants flower, and below which short day plants will flower. NB: remember: later research discovered it’s actually the length of DARKNESS which is critical to the plant.
daily rhythm Activity occurring every 24 hours (NB: zeitgeber(s) present!).
Day neutral plant A plant that flowers independently of the day length.
diurnal Most active during the day.
dormancy A state of temporarily reduced metabolism in plants.
endogenous rhythm Controlled by an internal timing mechanism (biological clock). It continues in the absence of environmental cues.
entrainment Process by which the internal clock is reset so that it is synchronised with an environmental rhythm.
exogenous rhythm Controlled by an external cue or stimulus.
free running period The length of an organism's activity period in the absence of external cues (zeitgebers).
free-running Occurring in the absence of environmental cues.
hibernation A period of suspended activity / very low metabolic activity during winter, generally to survive a lack of food.
jet-lag Condition caused when the endogenous circadian rhythm does not match external cues. Usually caused by travelling across time zones.
nocturnal Most active at night.
period The length of the activity cycle (how long it takes to repeat) of an organism.
phase shift A change in the starting time of a rhythm (but not its period).
photoperiod The day length; this is the most reliable indicator of time of the year.
photoperiodism The control of seasonal activity by day/ usually night length.
phytochrome A plant pigment that controls the photoperiodic response (measures the length of darkness / light). Comes in 2 forms, Pr and Pfr
short-day plant A plant that flowers when the night length is greater than the critical length (i.e. short day).
long-day plant A plant that flowers when the night length is shorter than the critical length (i.e. long day).
zeitgeber The external environmental cue used to ‘set’ the biological clock. In most species, this is the change from light to dark (or dark to light).
suprachiasmatic nuclei (SCN) A tiny region within the hypothalamus of the brain, connected by nerves to the eyes. Responsible for controlling the circadian rhythm in animals.
Created by: NZARoberts
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