on the Move
Does it Help Them Survive?
What Scientists Think —
There's no question
about it; lots of flowers open and close. There must be a why
behind what we observe. These kinds of responses
are important to plant survival!
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.
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.
flowers respond to daylength.
They open and close at different times of day depending on the hours
of available sunlight.
open and close in response to weather.
This includes humidity, temperature, sunniness/cloudiness.
open and close at the same time each day. (Where do you think
the four-'o-clock got it's name? How about morning glories?)
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.)
Go to the Plants in Motion Web site to watch cool mini-movies of flowers
opening and closing. (Click on "morning glory" and "daisy.")
How Does it Work?
this. It's mid-morning. The sun has begun to warm the petals on a flower.
As it does this, the pressure of the liquid inside cells at the base of
the petals increases. (This is called turgor pressure.) As the
cells expand and become rigid, they cause the flower to unfold.
2: When light hits outer flower petals it triggers a chemical called
auxin that causes cells to grow and expand. This causes to flower
opens. But because its inner petals are less exposed to light, those cells
remain the same and cause the flower to close once light is gone.
This! Investigate Daisies or Dandelions
and dandelions are examples of wildflowers that open and close in response
to light. Find some examples of either flower in your schoolyard. In the
afternoon, cover some of the plants with a box. Leave some other plants
uncovered. What do you predict you will find in the morning? What do you
find? How would you explain your results.
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