Journey North International Plant Study

Flowers on the Move
How 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!

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.

See how cool pollen looks up close!

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.

Some flowers respond to daylength. They open and close at different times of day depending on the hours of available sunlight.
Some open and close in response to weather. This includes humidity, temperature, sunniness/cloudiness.
Some 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?)

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.)

Video Clips: Watch Flowers Unfurl!
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?
Example 1: Imagine 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.

Example 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.

Try This! Investigate Daisies or Dandelions
Daisies 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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