How does Phototropism Affect the Growth in Green Plants?

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Author: Dr. Muriel Gerhard

Grade Level: 6th - 7th; Type: Life Science


To determine whether plants are phototropic and provide evidence to substantiate the project`s results. 

Research Questions:

  • What are tropisms and how do they affect the life of green plants?
  •  What is heliotropism? How does it differ from phototropism?
  •  Who was Frits W.Went and what did he discover that was of great significance in plant growth?
  •  What role did Charles Darwin play in the area of plant growth?
  •  What are auxins? What role do they play in plant growth?
  •  What does the unequal concentration of auxins produce? What does that result In?

On the information level, this experiment serves to acquaint students with basic information on one of the key processes involved in and crucial to the growth and development of green plants. One of the processes involved is photosynthesis which is key in producing food for the plant. Photosynthesis is defined as producing something in the presence of light. We know that plants respond to many different stimuli in their environment. These stimuli are gravity, water, touch and light. These responses are called tropisms. The plant’s response to light is called phototropism. All of these tropisms are crucial to the plants survival. From our own experience, we know that the roots of plants respond to gravity by moving toward the ground. Also from experience we know that these roots are hydrotropic, namely the roots search for water. If we were to look closely at some plants, we may see the tendrils of vines fastening themselves around trees and bushes. This is called thigmotropism, namely, a response to touch. In this project we are searching for clear cut evidence as to the effect of light on green plants. How do green plants respond to light? We know that they do, but how do they do it? In sum, although we may think that plants do not move, they do move, all the time, but very, very, slowly responding to various stimuli. Plants are on the move! We call it growth. If there is unequal growth on one side of a plant, will it bend toward the other side? What precisely has phototropism to do with this? What is required is evidence to substantiate this uneven growth, specifically the key role of light in this process. The task is yours. Your experimentation coupled with your research on auxins will serve to further explain the results you obtain and provide a clear picture of what is actually occurring. 

This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control when required, of identifying dependent and independent variables, of selecting a large enough sample of subjects when applicable to the objective, of accurate and organized data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as scientist.

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