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How plants tell time - Dasha Savage


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Morning glories unfurl their petals like clockwork in the early morning. A closing white waterlily signals that it’s late afternoon. And moon flowers, as their name suggests, only bloom under the night sky. What gives plants this innate sense of time? Dasha Savage investigates how circadian rhythms act as an internal timekeeper for flora and fauna alike.

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Thinking that plants are out there, figuring out the time of day, or the seasons in the year can be a lot to wrap your head around. Plants are actually pretty dynamic, and they move around a lot! They have complex mechanisms for not only detecting light, but also following light as they grow.

The main advantage of using light perception for flowering time in plants is for reproduction, so that birds and bees can pollinate flowers during the spring. Other animals use the amount of light during the day, or photoperiods, for knowing the optimal time of year for reproduction, and to prepare themselves for the harsh winter up ahead. Different plants (and different animals!) will have unique photoperiods to which they will respond.

What happens when circadian rhythms fall out of sync with an organism’s environment? We only have to think to that hour of sleep we lose during Daylight Savings Time to know that it doesn’t feel so great. If a plant’s flowering mechanism doesn’t turn on exactly when it needs to, it can result in less flowers, and less fruit. A night of interrupted sleep never feels the same as cozy rest and sweet dreams. Humans are less alert during the night, and this may be linked to certain health issues. Plants also feel the adverse effects of a restless night, in fact, phytochromes are key in sensing the absence of light. When the dark is interrupted, changes in plant growth patterns are a result.

Plants are pretty complex organisms, and researchers at institutions like The Carnegie Institution of Washington apply their green thumbs to molecular biology, to figure out exactly how those little guys in your garden are growing. Plant some seeds of your own and see what you can observe!

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TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Dasha Savage
  • Director Avi Ofer
  • Animator Avi Ofer, Axel Bunge
  • Script Editor Emma Bryce
  • Sound Designer Stephen LaRosa
  • Narrator Addison Anderson

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