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Orientation in time
as part of AS91603 NCEA L3 Biology
Term | Definition |
---|---|
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. |