How Does Gravity Affect the Angle that Radish Plants Grow?

Researched by Annie M.
2000-01
PURPOSE
The purpose of this experiment was to determine how gravity affects the angle that radish plants grow.

I became interested in this idea when my family planted a garden last summer. We planted it on a hill, and I wondered if the slope would affect the direction that the plants would grow.

The information gained from this experiment might help orchardists determine what would happen if they started an orchard on a hill.

BACK TO TOP

HYPOTHESIS
My hypothesis was that the plants placed at 0°, (being the vertical direction) would continue to grow upwards. The plants placed at other  angles  would turn and grow  upward.

I base my hypothesis  on a sentence off of the Internet  at http://w2.xrefer.com/entry/461222 that says "For example, if a stem is placed in a horizontal position, it will still grow upwards." 

BACK TO TOP

EXPERIMENT DESIGN
The constants in this study were: 
  • Same type of soil
  • Same size of container
  • Same amount of light
  • Same amount of water
  • Same way plants are measured
  • Same temperature
  • Same species of plant
  • Same amount of time to grow 
  • Same type of container


The manipulated variable was the angle in which each plant is placed to grow.

The responding variable was the angle that each plant stem grows.

To measure the responding variable, I will use a protractor and measure the stem’s angle, each day until the experiment ends. 

BACK TO TOP

MATERIALS
QUANTITY  ITEM DESCRIPTION
25  Disposable  300mL plastic cups
50 Radish seeds
7,500mL Potting soil
2  Pairs of nylon stockings
1  Camera/film
1 Protractor
1  Knife 
1 Fluorescent light source
50  Rubber bands 
1   Pencil
2 Thin boards
1  Old towel 
 25 White address labels
Duct tape

BACK TO TOP

PROCEDURES
Start Plants Growing
1. Use a sharp knife to cut a small hole in the bottom of each of the 25 plastic cups
2. Carefully pour 250mL  of potting soil into each cup.
3. Set two radish seeds on the top of the soil in every cup.
4. Add 50mL of soil on the top of the seeds.
5. Set all cups in a window area.
6. Water cups according to dryness until approximately 2-3cm high.
Experiment Set-Up
1. When plants are about  2-3 centimeters high, gather materials such as the board, nylon      stockings, tape, protractor, towel, and pencil.
2. Evenly space 25 marks with a pencil and a protractor along the board, 5 at each angle.        See diagram #1 below.
3. Label  the degrees marks as you make them. 
4. With the stickers and marker, label all 25 cups. (Label 5 with 0° , 5 at 45°, 5 at 90°, 5 at 135°, and 5 at 180°.
5. Set labeled cups aside.
6. Take the nylon stockings and cut 25 ( 5cm by 5cm) squares.
7. Cut a hole in the center of each square.
8. Stretch  each  nylon square over a cup and fasten it with  a rubber band.
9. Match  each labeled cup to a matching  labeled spot on the board.
10. Attach  each cup to it’s place and angle on the board with duct tape.
11. Lay a strip of towel at the bottom of the board to catch the water that will drip out when the plants are watered.
Doing Experiment
1.Water  whenever dry, with 25mL of water by turning the board upside down.
2. Observe the plants every day in Experiment Log.
3. Record measurements on data chart. 

BACK TO TOP

RESULTS
The original purpose of this experiment was to determine how gravity  affects the direction that radish plants grow.

The results of this experiment were that the control group of plants seemed to stay about the same, while the135° plant stems turned downward. All of the other experimental groups seemed to turn upward.

See the table and graph.

BACK TO TOP

  CONCLUSION
My hypothesis was that the plants placed at 0°, (being the vertical  direction) would continue to grow upward. Most of the plants placed at other angles  would turn and grow upward.

The results indicate that this hypothesis should be rejected.  Although  some of the plant stems did turn upward, the 135° plants seemed to turn downward. 

Because of the results of this experiment, I wonder if the amount of light used would affect the plant’s direction more than gravity. 

The information gained from this experiment can help orchardists to realize what might happen if they start an orchard on a hill. 

If I were to conduct this project again, I would use smaller pots, which would make taping the pots to the board easier. I also wouldn’t wait as long before turning the plants so that the stems wouldn’t be as long and would be easier to measure. Another thing that I would do if I could conduct this project again would be to find another easier and more accurate method of measuring the degrees or angle that the plant stems are pointed, then my data would be more accurate. I would also have more trials with  more plants per group.

BACK TO TOP


RESEARCH REPORT
 
 

Introduction

Have you ever wondered why you sometimes see a tree growing on a hill with all of its branches reaching up? This is called geotropism. 

Tropisms and Stimuli

Tropism is the bending movement in plants caused by the outside stimuli. Plants tend to orient toward most stimuli. The tropisms this cause this are referred to as Phototropism (light), Chemotropism (particular substances), Hydrotropism (water), Electrotropism (Electrical current), and Thigmotropism (mechanical stimulation). A plant’s response to stimuli is usually slow, but in order to survive a plant must be able to respond to a changing environment.

Geotropism

 Geotropism is the bending movement of plants caused specifically by gravity. It can happen when a tree for example, starts to grow on a steep hill. The tree would still grow upward, caused by the pull of gravity. Plant roots always tend to grow downward, so a germinating seed  can be turned upside-down, and the roots would still grow downward. This is also because of gravity. There are 3 types of geotropism: positive geotropism, negative geotropism, and transversal geotropism. The main root of any plant would be considered positive geotropism. An example of negative geotropism would be the main stem. 

Uses and Needs

 Plants can be used for many things. We can eat them, wear them, build shelter with them, and breathe the oxygen that they produce. Other things that plants can be used for are medicine, paper, soap, perfume, and photographic film. In order to grow correctly, plants need four major things; light, water,  soil, and nutrients. They also need to be able to respond to changes in their environment. With these things, plants can grow correctly and we can continue to thrive on them.

Stems

 There are 2 basic types of stems: the Herbaceous stem and the Woody stem. Herbaceous stems consist of only primary tissues, which are a result of the cell division at the top of the stem. Primary tissues consist of something called epidermis. Epidermis forms a waxy outer coating on the stem, that keeps the plant from drying out. Woody stems are hard and rough. They are usually brown and consist of Primary tissues that resemble those of a Herbaceous Dicotyledonous  stem. A more common name for woody stems is a tree trunk, because woody stems can be found in trees, bushes, and shrubs.

Photosynthesis

 Photosynthesis is the chief function of leaves. It means "putting together with light". During photosynthesis, many complicated steps take place, and the hydrogen mixes with carbon dioxide forming a simple sugar. This sugar is where the plant gets and stores its energy from. If narrowed down, the process of photosynthesis has five basic steps. The first thing that happens during this process is when the light strikes the chlorophyll in the chloryplasts. Oxygen is then released from the plant into the air. After that, energy from the light separates the water into hydrogen and oxygen. The hydrogen and carbon dioxide then combine together to form a simple sugar. After making this "plant food", water from the roots is obtained and the carbon dioxide from the air enters the leaf. The process then begins all over again!

Summary

 The study of geotropism is really very interesting. Since plants are an everyday thing, we should get to know more about geotropism and other types of tropism so that we can find more modern and interesting ways of growing things.

BACK TO TOP
BIBLIOGRAPHY

Carter, Joseph L. et al.  Life Science, Lexington MA

"Geotropism",     Available at http://w2.xrefer.com /entry/461222  November 8th, 2000

Hershey, David R. Plant Biology Science Projects  Canada; John Wiley and Sons Inc. 1995

Johnson, Gregory B.  "Tropism", World Book Encyclopedia, 1999

Keating, Richard C. "Stems", World Book Encyclopedia, 1999

Primack, Joel R.   "Gravitation", World Book Encyclopedia,1999

Sengbusch,  Peter V. "Geotropism or Gravitropism" Available at http://www.rrz.uni-hamburg.de/biologie/b-online/e32/32c.html  November  11th , 2000

Weber, Joseph. "Gravitation" , Encyclopedia Americana, 1999
 

ACKNOWLEDGEMENTS

I would like to thank my parents, for purchacing many  of the materials that I needed to conduct this project. I would also like to thank my teacher, Mr. Newkirk, for helping me to solve many problems that I faced while performing this experiment.

Top of page

Menu of 2000-2001 Science Projects

Back to the Selah Homepage