Introduction: (Initial Observation)
When plants grow, the stem and leaves grow upward while the roots grow downward? The direction that a plant grows has nothing to do with the way that you plant a seed. Stems always find their way up and roots always find their way down.
Why is that? How does the plant know which way is up or which way is down? Is it because of soil moisture? Light or gravity?
In this project, you will study the effect of gravity on plant growth.
cIf plants grow up, because gravity pulls down, then how do they grow in zero gravity or very low gravity? Can astronauts grow their own food plants during long trips through space?
Information Gathering:
Find out about plants and factors affecting plant growth. Read books, magazines, or ask professionals who might know in order to learn about the affect of gravity on plant growth. Learn about growing seeds and gravity sensor cells in the root of plants. Keep track of where you got your information from.
Also Click Here to see a similar project for the effect of gravity on plant growth.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to see if gravity affects plant growth.
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The independent variable is the gravity. The dependent variable is the direction of plant growth. Controlled variables are the amount of water, light, and nutrients.
Hypothesis:
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are some sample hypotheses:
- Gravity is the main factor affecting the plants direction of growth. My hypothesis is based on my observation of plants growing in rooms with lights coming from the sides and plant continues to grow up.
- At the absence of gravity, plants grow at the same rate but in a random or unpredictable direction.
- At low gravity or no gravity conditions, plants grow faster because gravity can potentially slow down the movement of water and nutrients up the stem.
What do you think? What is your hypothesis?
Note that hypothesis does not have to be true. Your experiments may reject or support your hypothesis later.
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: The effect of gravity on seed germination and plant growth.
Introduction: In order to see the effects of gravity on plant growth, you can grow seeds in the dark and see the direction of roots and shoots.
Material:
- 10 chick-peas, beans or radish seeds
- 10 small cups or jars with straight sides
- Water
- Paper towel
- Pieces of aluminum foil
- Marker
- Tape (if necessary)
Procedure:
- Place the beans in a bowl of water and let them soak overnight. This can accelerate the seeds germination.
- Take a sheet of paper towel and fold it in half and take that half and fold it in half to make a perfect square.
- Place one seed on the middle of folded paper towel.
- Roll the paper towel up.
- Moisten the paper towel a little.
- Wrap an aluminum foil around the paper towel and tape the foil. This will hold the paper roll and helps maintain its moisture.
- Place the roll into a cup. Add about 1″ water to the cup.
- You need to make 10 rolls like this with one seed in each roll and each roll in a separate cup.
- Number the cups from 1 to 10. Use the marker to mark the side of the rolls that are up. Leave the cups for 5 days in a warm place in your room.
- After 5 days carefully open roles number 1, 2, 6 and 7 (one at a time) and observe what had happened. Do not change the position or orientation of the seeds. Carefully roll back the paper towels and place back the foil and tape.
- If any cup has less than one inch of water, add some water to that.
- Turn the rolls 1 to 5 up-side-down in their own cups and leave the rolls alone for another five days.
- At the end of the second 5 days, open all the rolls up one last time and observed what has happened.
This is a sample of data table for your first observation.
| Seed # | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Direction of roots | ||||||||||
| Direction of shoots |
Fill up the above data table by typing Up or Down for the direction of roots and shoots for each seed.
A similar data table may be used for your second observation.
Experiment 2 (Optional): The effect of zero gravity on seed germination and plant growth.
Introduction: In order to simulate zero gravity in our experiment, we may grow a plant (or a group of plants) while rotating the growth chamber. With this method, before the plant cells be able to determine the direction of gravity, it is already changed.
Procedure:
Setup a wheel, cylinder or pipe that can spin slowly around its horizontal axis. Mount one or more growth chambers on the wheel or in the cylinder. Make sure each growth chamber has one seed. Let the device spin slowly.
Stop the device once a day for a few seconds to add water or make observations.
Additional Notes:
The details of your instrument may vary based on what may be available to you.
Spinning wheel can be an old gramophone placed on the side. Or it can be a round plastic disk spinning freely around a nail passing its center. The source of rotational force can be a small electric motor or drops of water (like water wheel).
The growth chamber can be two folded and moistened paper towels sandwiched together with a seed in the middle. You can also wrap them in aluminum foil to preserve the moisture.
The growth chamber can be attached to the wheel by pins or tape.
Materials and Equipment:
List of material can be extracted from the experiment 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.
Calculations:
No calculation is required for this project.
Summery 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.
Partial/ sample results for experiment number 1: After 5 days the bean sprout roots started growing down and the stem up. Flipping the roll made the beans do a 180-degree turn, and again the roots started to go down and the stems up.
Conclusion:
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.
Does gravity affect the direction in which plants roots and shoots grow?
Your further research can show the reason why gravity has this affect on plants. You may also discover that movement of a plant due to the pull of gravity is called Geotropism.
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.
References:
List of References
