Some flowers open only once, as they grow from a bud to a full-blown blossom. Tulip flowers are different. On sunny days with cool nights, the tulip flower can open and close right before your eyes!

Tulip plants are sensitive to ____________ and temperature. As morning temperatures __________, tulip flowers open. By mid-day, insect pollinators are out looking for flowers. Insects visit the colorful yellow and purple parts inside the open tulip flower, and ____________ can occur.

As nighttime approaches and _____________ decrease, tulip flowers _____. The closed petals protect the inside of the _______ from cold temperatures and unwanted insects.

Internal signals also determine when some flowers _______ and close. A 24-hour _____ of opening and closing is controlled by the plant’s biological clock. This activity is known as a plant’s “circadian rhythm.”

Now each spring as you observe the opening and closing flowers of the tulip plant, you will know that both the ___________ (sunlight and temperature) and the plant’s internal _________ work in __________ to make it happen.

Word Bank

temperatures

rhythm

sunlight

pollination

cycle

open

close

increase

harmony

flower

environment