Plants Are On The Move! A Study of Gravitropism

Abstract

As we humans zip from place to place, we often forget to stop and smell the roses. Compared to our fast-paced lifestyle, plants seem rooted to the spot. Don't be deceived by appearances however, plants are on the move! This experiment will investigate the stimulus/response relationship in plants and prove that plants can move up and down in response to gravity.

Objective

The goal of this experiment is to measure a plant's response to gravity using time-lapse photography.

Credits

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Last edit date: 2020-06-23

Introduction

Through careful observation, scientists have found that plants do move—they just move at a much slower pace than we humans. Using time-lapse photography, scientists have discovered that plants seem to know the difference between up and down, light and darkness, and that they can move in response to these stimuli.

A stimulus is an agent that directly influences the activity of a living organism. Plants often move in response to a stimulus. For example, a Venus flytrap will snap shut (response) when an insect (the agent) touches (stimulus) sensitive hairs on the plant's leaves.

These automatic movements are called tropisms. The movement of a plant's leaves and stems growing upward and the roots growing downward in response to gravity is called gravitropism (also called geotropism). When a plant's leaves turn toward the sun, the movement is called phototropism. Plants even seem to have a sleep cycle! When a plant closes its leaves or petals each night, the movement is called the plant's circadian response. How do plants know when to sprout in the spring? A plant's movement in response to seasonal changes in temperature and light is called photomorphogenesis.

In this plant biology science fair project, you will investigate a plant's response to the stimulus of gravity and prove that plants are on the move!

Terms and Concepts

• Time-lapse photography
• Stimulus
• Response
• Tropism
• Gravitropism
• Phototropism

Questions

• Why do plants move?
• How do plants move?
• What types of plants move?
• What parts of plants move?

Materials and Equipment

• at least 6 mature Coleus plants in pots
• digital camera
• large box
• heavy duty tape
• dark blanket
• a small box or stack of books.
• utility knife
• Information on selecting a camera and making time-lapse movies from Plants-In-Motion: http://plantsinmotion.bio.indiana.edu/plantmotion/starthere.html

Experimental Procedure

1. Make sure all 6 Coleus plants are in good health and have been watered recently. The soil in the pots should be damp throughout the experiment.
2. Obtain a box large enough to hold three Coleus plants that are laid on their sides.
3. Place 3 of the Coleus plants on their sides in the box. The plants should not be touching.
4. Take a picture of the plants.
5. When the box is closed, no light should reach the plants. If necessary, the box can be placed in a closet or covered with a dark blanket. You are trying to see if the plants will respond to gravity by observing the movement of their leaves and stems up and their roots down. If any light can peek in for more than a few minutes, the plants will also move in response to the light (phototropism) and that would ruin our results!
6. Cut a hole large enough for the camera lens and flash of your camera in the side of the box. Carefully attach your camera to the box with tape if needed. You may want to rest your camera on a stack of books or a smaller box during the experiment.
7. Test your set-up by taking a few pictures of your plants. Make sure that your flash is on!
8. Place the other 3 Coleus plants on their sides in a location where there is a normal day/night light cycle. All other conditions (temperature, humidity, etc.) should be as close as possible to your experimental conditions. These will be your control plants. These plants will be exposed to both light and gravity and should respond to both stimuli.
9. Take pictures of your experimental plants every half and hour for a period of 6–24 hours. The longer you conduct the experiment, the more movement you will see. Some cameras can be set to automatically take pictures at regular intervals—check out the options and settings on your camera.
10. Take a similar series of pictures of your control plants. It is best to conduct the experiments at the same time, but this will be difficult unless you have two cameras. If you have a single camera, do your experiment sequentially, taking a series of pictures of your experimental plants on one day, and of your control plants on the next day.
11. When you are finished with the experiment, compare your before, during and after pictures from each plant by developing your photographs or by using a digital imaging program. Did your experimental and control plants behave differently? What parts of the plant moved? Did some parts of the plant move more than others? Can you deduce that your experimental plants moved in response to gravity? How?

For information on how to choose an appropriate camera for this project and how to make a time-lapse movie with your pictures go to Plants-in-Motion:
http://plantsinmotion.bio.indiana.edu/plantmotion/projects/projects.html

If you like this project, you might enjoy exploring these related careers:

Variations

• Because you took flash pictures of your plants, they were not in complete darkness for the entire experiment. Can you think of a method to show if the camera flash has an effect?
• Using the same experimental setup, investigate the effects of light on plant leaves and stems by cutting small hole in the side of the box and introducing light through the hole.
• Investigate the movement of the Venus flytrap or the mimosa plant by stimulating the plants by touch.
• Conduct research on plants that have a strong circadian response and change the amount of time that the plant is exposed to daylight. See if you can change the natural circadian response of the plant.
• Tulips in December? See if you can "force" tulips or other bulbs that typically bloom in the spring to bloom during a different time of year by providing the temperature and light stimuli needed to trigger photomorphogenesis.

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