By Amy Elkin

How the Environment Impacts Root Growth

Big Question Which effects root growth more gravity or

soil nutrients?Reasoning: To determine if the roots of

plants grow down because of gravity, because that is where the soil is, or because of some other reason.

Hypothesis and Reasoning Hypothesis: Root growth is effected by gravity more

than nutrients found in soil. Reasoning: I believe this hypothesis to be true since

gravity makes the roots of plants grow down and the stem of the plants grow up. In the past I have seen roots growing downward in plastic bags containing wet paper towels.

Interesting Facts Many seeds will grow even if there is little light Geotropism is the growth of a living organism in

response to gravity Roots bend in response to gravity because of the

hormone auxin Roots do not need soil to grow, some can grow in

plastic bags containing wet paper towels Radishes are one of the fastest growing types of

seeds

Experiment: Materials 1 package of radish

seeds1 roll of paper towels1 package of small white

labels18 CD casesModeling clayPotting soilShallow cooking trayLab notebookRulerBlack marker and brown

marker

Computer paperPenPencilComputerEye dropper filled with

waterCameraCD rack Plastic cupPrinterComputer paper

Experiment: Instructions1. Fold 6 paper towels to the size of the CD cases.2. Place the paper towels inside each CD case.3. Write “up”, “down”, “left”, and “right” each on 6 different white labels.4. Label each CD case with one of each of the labels, on the correct side.5. Fill 3 of the CD cases halfway with potting soil.6. Wet the paper towel in each CD case with 3 drops of water.7. Place six seeds in each CD case. In the three cases with the potting soil, place the

seeds directly against the edge of the soil.8. Close the CD cases tightly.9. Use 6 additional labels to label the horizontal cases #1 to #6.10. Using the modeling clay, and CD rack, place CD’s #1, #2, #3, #4 in a vertical

position with the “up” label at the top inside the cooking tray.11. Using the modeling clay, and CD rack, place six CD's labeled horizontal #1 to #6 in

the cooking tray12. Take measurements and photographs of the root growth every 2 days.13. Take pictures of changes in CD's.14. Every other day, rotate cases labeled "rotation" 90 degrees clockwise.15. Note whether the root growth is affected by the direction of gravity or the presence of

soil.16. Record root growth and direction by day for each of the CD cases.17. Repeat the entire procedure (Steps 1-16) two more times to make sure the results

don’t change.

Control Group/Variables Control Group: paper towels in horizontal

position Variables: soil group in different positions

Vertical group grew mainly down

Some grew diagonally down after growing up

Most grew towards gravity

Observations

The ones with soil in the vertical group grew in random directions or did not grow

Observations

The roots in the horizontal group mostly grew in random directions or did not grow at all

Only a few of the roots in the rotation group grew down and a lot of them either did not grow or grew in random directions

DataGrows

Toward Gravity

Grows Toward

Soil

Random Growth

Direction

No Growth

1 Paper Towel Horizontal 1 3 2

2 Soil Horizontal 3 3

3 Soil Horizontal 2 4

4 Paper Towel Horizontal 5 1

5 Paper Towel Horizontal 5 1

6 Soil Horizontal 6

7 Paper Towel Vertical 4 2

8 Soil Vertical 1 2 3

9 Soil Vertical 1 5

10 Paper Towel Vertical 4 2

11 Paper Towel Vertical 5 1

12 Soil Vertical 6

13 Paper Towel Rotation 1 1 4

14 Soil Rotation 2 4

15 Paper Towel Rotation 2 2 2

16 Soil Rotation 6

17 Soil Rotation 1 5

18 Paper Towel Rotation 3 2 1

# of SeedsDisc

NumberType Orientation

Almost half the seeds did not grow30 of the seeds that did grow, grew in random directionsOnly one seed grew towards the soil

Analysis of Data

Grows Toward Grav-ity

Grows Toward Soil Random Growth Direction

No Growth0

10

20

30

40

50

60

Figure 7: All CasesN

umbe

r of

See

ds

The cases with soil had the least seed growthThe cases with paper towels positioned vertical had the most

growth toward gravitySeeds in horizontal cases with paper towels mostly grew in

random directions

Analysis of Data

Horizontal Case with

Paper Towel

Vertical Case with

Paper Towel

Rotation Case with

Paper Towel

Horizontal Case with

Soil

Vertical Case with

Soil

Rotation Case with

Soil

02468

1012141618

Figure 8: All Cases

No GrowthRandom Growth DirectionGrows Toward SoilGrows Toward Gravity

ConclusionMy hypothesis was correct. Gravity had a greater

impact on root growth direction than soilThe only consistent direction of root growth was

toward gravity when the CD case stayed in a vertical position

The random growth in horizontal CD cases shows the roots didn’t know which way to grow

Soil is important for normal root growth because it holds water

References www.ag.arizona.edu/pubs/garden/mg/botany.environmental.html (September, 2009) Environmental Factors That Affect Plant Growthwww.en.wikipedia.org/wiki/Geotropic (September, 2009) Gravitropismwww.ksnn.larc.nasa.gov/webtext.cfm?unit=plants (September, 2009) Exploration Systemswww.library.thinkquest.org/C003763/index.php?page=human03 (September, 2009) Gravitational BiologyParker, S. (1995) Isaac Newton and GravitySpilsbury, L. (2008) Plant HabitatsTagliaferro, L. (2007) The Life Cycle of a Beanwww.uoregon.edu/~melliot2/plants/gravity.htm (September, 2009) Gravitywww.esmdeo.arc.nasa.gov (September, 2009) Gravity and Plants