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Why do plants move?

Why do plants move?

Introduction: (Initial Observation)

Look at the picture. Why all pansy flowers are faced the same direction? I checked them in the morning, noon time and even in the afternoon. It seems they are all looking at the sun.

Even though I first noticed that in the Pansy flowers, it is not limited to pansies and viola. All flowers move. Some are just more noticeable.

When I first noticed such a movement, I simply thought plants are smart and will decide which way to face. Later I thought it might be the power of sun that makes them move. But now I want to find out real reasons behind such peculiar movement.

Plants move is not just a response to light. Even if you knock over a plant, soon the leaves will have turned upward and the roots downward. They respond to touch, too – if you touch a plant on the same side every day, it will grow away from that side, trying to get away from objects and toward open space.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

Find out about plants and their moves. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

The question of how or why Plant move? is not a new question. In my Internet search I found a document (http://archive.showmenews.com/2001/Feb/20010216News029.asp ) that shows even Darwin was wondering and studying about plants movement.

More research showed that such involuntary response of an organism, or part of an organism, involving orientation toward or away from something is called tropism.

If you do more Internet search using the keywords tropism and plant, you will find that depending on the type of stimuli that causes tropism, we have different types of tropism. For example plant movement cause by light is called phototropism and plant movements caused by gravity is called geotropism. Also search to see what is thigmotropism and hydrotropism?

Question/ Purpose:

The purpose of this project is to see why and how do plants move?

Identify Variables:

Variables that may cause or affect movements of plants are light, gravity and touch.


My hypothesis is that under certain conditions (light, water, gravity,..), one side of the plant will enlarge or shrink and that will make the plant tilt toward the shrunken side or opposite the enlarged side. For example in the morning, the side of the plant that is toward sun, will lose some water and molecules will shrink, as a result the plant tilts toward that side.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

As your first experiment, you want to build a model that shows how plants move (This is called Tropism).

You will need the following materials:

  • Your hands

Procedure (what to do):

  1. Clasp your hands together in front of you, keeping your elbows together and your wrists nice and relaxed.
  2. Keeping your right hand still, push upwards with your left.
  3. Remember to keep your wrists relaxed

Q: What happened?

  • Did your hands tilt to the right?

Now do the opposite, keep your left hand still and push up with your right.

  • Did your hands tilt to the left?


You have just done what plants do every time they want to grow somewhere!

They stop growing on the side of the stem where they want to turn and keep on growing on the other side. This causes them to tilt in the direction they want to grow, just like your hands!

Building a Model of a Plant to see how plants grow

Introduction: Often students want to construct a model in order to show how plants move. We had an old experiment that use a balloon inside a slinky spring in order to demonstrate plant movements. As time passed we noticed that some students have a hard time to find a good combination of balloon and slinky for their experiment. This new experiment will only use two balloons and some connecting plastic pipes that are easily available to most students. This experiment will show how do the plants bend to the side that is not growing.


Get two identical balloons and connect them to the ends of two 2-foot tubes.

The other ends of tubes will later be used to inflate the balloons as needed.

Use some masking tape to hold the tubes side by side and hold the balloons in place.Slowly blow in both balloons so they will stand straight.
Use another piece of tape to connect the top of the two balloons. In this way two balloons together will act as the stem of one plant. Each balloon will represent one side of the stem.

At this time both balloons have some air so they will stand straight.

Use some extra tape to mount your setup on the sides of a box or any other vertical object. In this way the balloons will stand upright.
Start blowing the balloon on the right while observing the top of the stem.What happens when you slowly inflate the balloon on the right?

The more you inflate the balloon in the right, the more the stem bends to the left.

The great thing about this model is that it also represents the main force used by plants to move, that is internal pressure acting on a semi-rigid box.

In the case of the balloon, air pressure is the force that cause elongation. Real plants use water pressure, or in scientific terms, “hydrostatic pressure”, to get their cells to elongate.

Do plants move as a response to light?


How does a plant respond to light?

Experiment 2:

To find the answer to this questions we design a simple experiment to see how does the stem segment (called the “hypocotyl”) of a young seedling responds to the light. In this experiment we place a young seedling in a dark chamber with only one small window on the side to see how does the plant react to the light entered from the small window. We have decided to use black film canister as a dark chamber and punch a hole on it’s side as a window. You can use any thing else such as a small box or plastic cup for this purpose. If what you have is clear, cover it with aluminum foil or black paper so inside your chamber will be dark and the only light source will be the small hole that you make. Here are some details:

Procedure (what to do):

First you’ll need to grow some seedlings for the experiments.

If you’ve never done this before, it is very easy to do and seedlings can be grown in a greenhouse or in relatively warm and well-lit areas, such as near a window.

  • Place a layer of paper toweling at the bottom of a container (or a seed tray or flowerpot) .
  • Add about 2 inches of potting soil and moisten the soil.
  • Sprinkle a few radish seeds on the top of the soil.
  • Add a thin layer of soil on the top.
  • Water again lightly to make sure that you don’t uncover the seeds.
  • Place Saran wrap on top of the container until the seedlings emerge (this may take a day or two).
  • Keep a pan of water under the container and water if needed from the top.

Preparing the Chambers

  • To make a “window’ in your chamber, punch a hole in the side of the film canister or any other dark box that you may have.
  • If you are using clear material for chamber (like a plastic cup), cover it with aluminum foil to make it dark inside.

Setting up the Experiment

  • Cover your plant with the dark chamber. Make sure the window of the chamber is open for some light to enter.
  • Leave the plants in this position for a few hours, then carefully open the chamber and look at the seedlings.
  • Water your plant if necessary, close the chamber and observe again after one day, two days, three days etc.
  • While you are waiting to observe the results, you can make predictions about what you expect to happen.

Making Predictions

Instead of just waiting to see what the plants will do, you can make predictions about the possible outcomes.

In the chambers with the “window” on the side

  • Q: Do you think the stem will grow toward or away from the “window” (light source)


You can design additional experiments on your own to test other hypotheses. For example, will the seedling still respond to light if it is a certain color? To test this hypothesis, different colors of cellophane can be placed over the window in the canister.

Another experiment

In the previous experiment we were able to observe a move in plant just in a few hours. Even if we be more precise, we can notice slight move in just a few minutes. Such move are so fast that we can not relate it with plant growth. In other words such moves are definitely caused by the direction of the light source (window). In this experiment we will see the moves that are long term moves and happen as plant grows.

This experiment will demonstrate how plants react to the presence of light.


  • Shoebox with a lid or cardboard box with dividers
  • Paper cup
  • 3 bean seeds
  • Cardboard cut to width of shoebox
  • Potting soil
  • Scissors
  • Tape or glue



  1. Fill the paper cup with potting soil.
  2. Plant the beans in the soil. Plant about 1/2″ deep.
  3. Water the soil and allow the beans to sprout.
  4. Stand the shoebox on its narrow end.
  5. Cut two cardboard pieces that fit inside the shoebox, these will be the maze walls so put alternating holes in them big enough for the plant to get through (approx. 2″).
  6. If using a cardboard box cut alternating holes in the divider. Holes should be about 2 inches across.
  7. Make sure the walls will stay in place with tape or glue.
  8. Cut a hole in the top that is big enough for the plant to get through.
  9. As soon as the plant sprouts put it inside the shoebox at the opposite end from the hold you have cut.
  10. Put the lid on the shoebox and make sure it will remain in place.
  11. Place the box near a sunny window.
  12. Open the lid daily to make note of plant growth.
  13. Water the soil when needed.
  14. Continue to observe until the plant grows out the hole in the lid.


  1. Do you think the plants will wind their way through the holes to the outside of the box?
  2. What does this experiment tell us about how plants respond to light from the Sun?
  3. Are the plants sensitive to gravity?
  4. How can you tell they are sensitive to gravity?
  5. Which way do the stems always grow?
  6. Which way do the roots always grow?
  7. Do you think that turning the seed upside down would affect the way the plant grows?
  8. List three things that are necessary for plant survival.


The plant winds around all obstacles and out the hole in the lid just to get to the light.

If the seed were planted upside down, the roots would start growing from the top of the seed and the stem would come out from the bottom. Then they would both turn around and grow the correct way. The roots would grow down because of gravity (geotropism) and the stem will always grow toward the Sun (phototropism).

Plants need gravity, light, and water for survival. Plants will also grown toward favorable conditions and away from unfavorable conditions.

The light energy from the Sun causes the plants to produce food in their leaves by photosynthesis. This enables them to grow.

Do plants move as a response to gravity? (Geotropism)
(is recommended for higher grade students only)

Now we want to see the effect of gravity on plant movement (geotropism or Gravitropism).

Experiment 3:

In this experiment we want to see the effect of gravity on movement of plant.

Select one of your young seedlings with straight stem. Turn it on the side and cover it with a dark chamber with no windows. You want to see if the stem goes up or down as a result of gravity. We cover the plant by a dark chamber to make sure that any movement of plant is not caused by light.

Check the plant after a few hours, after a day and after 2 days. Report the results.

Materials and Equipment:

Can be extracted from the experiments section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


No calculations are required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List your book and online references in your report.