Like animals, plants sense changes in their surroundings and respond to them. Plants are able to detect and respond to light, gravity, changes in temperature, chemicals, and even touch. Unlike animals, plants do not have nerves or muscles, so they cannot move very fast. A plant usually responds to change by gradually altering its growth rate or its direction of growth. The slow movements that plants make towards or away from a stimulus, such as light, are known as tropisms. Tropisms are controlled with the help of special chemicals called PLANT GROWTH REGULATORS.


Light influences how shoots grow. They bend towards it, so that leaves will have the maximum amount for photosynthesis. Roots push down through soil because of the effect of gravity. They may also be drawn towards water, or away from bright light. Other factors, such as temperature and how wet the soil is, may affect when seeds germinate (sprout).


Over the course of a day, the flowerheads in a field of sunflowers gradually turn, tracking the Sun’s path across the sky. The movement is almost too slow to notice. In the morning, the flowerheads all face east and by evening they face west. This is called phototropism, which means the movement of part of a body towards light. It happens as chemicals shift from one side of the stems to the other.


Many plants only bloom at certain times of year. They flower at the right time by responding to changes in light and temperature. A crocus plant is able to detect signs of spring, such as lengthening days (more light) and warmer soil (increased temperature). These changes cause chemical changes in the plant and the crocus starts to put out shoots and flowers.


Deciduous plants such as Forsythia respond to the lack of light and warmth in winter by entering a resting period. In preparation, the plant produces chemicals that weaken the leaf stalks, so the leaves fall. Over winter, the plant does not need to make food. Its shoots and buds are inactive. When spring comes, the plant produces chemicals that make buds and shoots start to grow again.


Some plant parts respond to contact. Climbers, such as pea plants and this passion flower, put out long, reaching shoots called tendrils. When a tendril reaches something solid – such as a garden cane or the stem of another plant – it coils around it. By grasping at supports in this way, the plant is able to climb even higher.


Roots usually respond to light by growing away from it, but the roots of mangrove trees behave differently. Mangroves grow in coastal swamps where there is little oxygen in the waterlogged soil. Their roots compensate for this by growing upwards out of the mud. Each low tide, the mangrove roots are exposed to the air and can collect plenty of oxygen.


Certain chemicals influence different aspects of a plant’s growth. These plant growth regulators may control how fast cells divide, or how they grow. Some are produced in the tips of shoots or roots. They can even change the direction the shoot or root takes as it grows. If cells on one side of the tip grow faster, the tip will start to curl in the opposite direction.

Copyright © 2007 Dorling Kindersley


Special Books for the Kids You Love
Celebrate 20 years of sharing love to the moon and back with the anniversary edition of Guess How Much I Love You, one of the world’s best-loved picture books. Plus, search our Book Finder for more great book picks. Brought to you by Candlewick Press.

Vote Now for the Children's & Teen Choice Book Awards
Voting is open now through May 3 for the Children's and Teen Choice Book Awards — the only national book awards program where the winning author, illustrator, and books of the year are selected by young readers. Encourage your child to vote for his favorites today!

Top 10 Math & Science Apps for Your Whiz Kid
Looking for the best math and science apps for kids? Check out these cool apps for all ages, which will grow your child's love of the STEM subjects (science, technology, engineering, and math).

Registered for Kindergarten — Now What?
Wondering what to do now that you've signed your child up for kindergarten? Try our award-winning Kindergarten Readiness app! This easy-to-use checklist comes with games and activities to help your child build essential skills for kindergarten. Download the Kindergarten Readiness app today!

stay connected

Sign up for our free email newsletters and receive the latest advice and information on all things parenting.

Enter your email address to sign up or manage your account.

Facebook icon Facebook icon Follow Us on Pinterest

editor’s picks