Study of Phototropism and Geotropism in Plants

Our Objective

To study the phenomenon of phototropism and geotropism in plants.  


The Theory


The mechanism known as phototropism causes plants to bend toward the light. The plants need light to promote the process of photosynthesis, which produces energy. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi.  A hormone called auxin, which responds to phototropism is present in the plant cells that are furthest away from the light and react to produce more protein and generate energy for the plant. This causes the plant to have elongated cells on the furthest side from the light. Almost all plants respond to photosynthesis in order to get more nutrition and energy.  

Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Positive phototropism typically causes the stem and shoots to shift toward the sun, whereas negative phototropism causes the roots to turn away from the light source. 


Geotropism is the movement or growth of plant parts in response to the force of gravity. Stems of the plant show negative geotropism while the roots show positive geotropism. Positive geotropism is the movement of plant parts in the direction of the gravitational attraction, whereas negative geotropism is the movement of plant parts against the direction of the gravitational pull. Since they develop in opposition to the gravity's pull, it helps the plant shoots stand upright. Root geotropism provides multiple advantages to a plant's vitality and survival. 

The root tip displays positive geotropism (grows in the same direction as gravity) and this is because the bottom side of a horizontally positioned root contains more auxin and they grow less, which causes the root to grow downward or in the direction of gravity. Auxin inhibits the growth at bottom of cell and promotes growth at the top of the cell. 

Learning outcomes 

  • Student understand the idea of phototropism and geotropism in plants. 
  • Student understand types of phototropism and geotropism in plants. 
  • Students will be able to do the experiment more accurately in the real lab once they understand the steps through the animation and simulation.