Thank you for your question.
"Flowers exist for one purpose only
What is it? To ensure that the plant reproduces and passes on its
genes. For many flowers, insects unknowingly move pollen from bloom to
bloom as they search for sweet nectar. This enables plants to make
seeds for the next generation. When flowers open and close, they
improve their chances of being successfully pollinated.
When Do Flowers Open and Close?
Scientists have a word for this opening and closing of blossoms and
the folding and unfolding of leaves: nastic movements. Different
flowers respond to different types of stimuli."
What About Tulip Flowers?
Tulip flowers open and close in response to heat and light. When tulip
petals fold in at night, or on a rainy day, the pollen stays dry and
reproductive parts are protected. When they open the next morning, the
pollen is ready to attach to the bodies of hungry insects. (From there
it is moved to another flower.) Younger flowers are more likely than
older ones to open and close like this. How would you explain that?
(Hint: Think about the flower's purpose.)"
"Movements of plant parts in which direction of movement is
independent of the direction of the stimulus that induces them. With
photonasty the stimulus is light. For instance, at constant
temperature Crocus and tulip (Tulipa) flowers open in the light and
close in the dark because of slight growth movements. Opening is
caused by epinasty ? i.e. greater growth of the upper surface of a
plant organ?and closed by hyponasty ? i.e. greater growth of the lower
surface of a plant organ. Similarly, at constant light intensity
crocus and tulip flowers show thermonasty; i.e. they open in warm air
and close in cool air."
tulip open close nastic movement