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Name: Khadija
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 2001-2002

Why do some flowers close at night and open during the day?

see the following:

Plant movement responses to temperature (thermonasty) and daily rhythms of light and dark (nyctinasty)

circadian rhythms

Anthony R. Brach, Ph.D.

There is a mechanism which causes this to happen, but your question is why , not how, so I will respond to that.

It appears that animal and plant evolution has pointed in the direction of survival and procreation. In the case of both animals and plants, those activities which promote survival and procreation endure and others are lost by lack of survival or procreation.

The specific activity you mention involves procreation. The theory is that a plant will have its flowers open and available for fertilization by insects, if that is the normal mode of fertilization for the particular plant, and the flowers will close at other times to conserve resources. In the case you describe, it is likely that the insects which visit and fertilize those flowers visit during the daytime hours, so there is no benefit to the plant to have them opened at night. A plant often produces scents to attract insects, and if the flower closes at night when the insect might not be around, resources are conserved because the scent will not be wasted as it volatilizes into the night air.

Naturally a lot of this is theory but it is consistent with many of our own choices in life which support our own survival with the least possible expenditure of resources or energy.

Good question, thanks for using NEWTON!

Ric Rupnik

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