Interesting Science Fair Projects: Gravitropism Experiment

In this lab, plant geotropism and the way roots respond to gravity will be studied. How does gravity play a significant role in a plant’s growth and development?

Objective

In this lab, plant geotropism and the way roots respond to gravity will be studied. How does gravity play a significant role in a plant’s growth and development?

Background Research

A “tropism” is an environmental stimulus that triggers plant movement. A common example of this tropic response is when a plant’s roots grow downward and its shoots grow up. This type of growth will continue even after a plant is turned sideways or upside down. The reason for this comes from the natural response of plants to gravity.  

There are three main kinds of geotropism: positive, negative, and transversal. Positive and negative geotropism refers to the up and down direction that plants/plant roots grow in, while transversal denotes growth that is vertical to the shoot’s axis. Any other angle of growth is termed plagiotropic.  

The process of geotropism can be summed up in three phases: perception, transduction, and response. 

Firstly, perception is the sensing of the environmental stimuli. Organisms perceive and gain information about elements and properties of the environment that play a role in the plant’s life. Specialized cells known as statocytes mediate the perception of gravity by root tips.  These statocytes contain small bodies of starch-filled organelles known as statoliths, which sediment to the bottom of the cell due to gravity and initiate differential growth patterns. 

From here on, the statocyte’s job is to communicate with the other parts of the root. The process of signal transduction converts the physical contact of statoliths into chemical signals, which allow for communication between other cells. 

The last part of this process is the ultimate response of the growing root cells to the signal indicating which direction is down. By knowing which way is down, the roots will start to grow towards the central influence of gravity. 

Materials
2 potted pea plantsWell-lighted, optimal plant condition environmentWater
Procedure
1) place two thriving, nearly identical pea plants (at about the same stage of development) side-by-side in a well-lighted, optimal plant environment room. Make sure to water them daily.
2) Take one of the pea plants and lay it on its side, so that the shoot of the pea plant is facing left or right instead of upwards.
3) Take note of any movement or response made by the plants due to geotropism. By the end of a few days’ time, the sideways plant’s shoot should start facing upwards.

Controlled Variables:

  • Vertical pea plant, shoots growing upwards and roots growing downwards (normal)
  • Amount of water given to each plant
  • Amount of sunlight given to each plant
  • Stage of growth each plant is in
  • Height of plant

Measured Variables:

  • Qualitative observation of plant’s response to geotropism
  • Quantitative measurement stating correlation between time of day and direction of plant’s shoots

Data 

4 a.m.

8 a.m.

12 p.m.

4 p.m.

8 p.m.

12 p.m.

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7

  Check the plant reguarly at four-hour intervals (may change), each time recording the time (labeled at top), day (labeled at left), and any notes or movements of plant (in the blank spaces). It would also be helpful to take pictures of the plants every four hours for better comparison and visual data of geotropism.

Conclusion

  • Does phototropism have a greater affect than geotropism (could phototropism interfere with experiment)?
  • Does altering a plant increase the rate of growth?

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