Study of Phototropism and Geotropism in Plants

Objective

To study the phenomenon of phototropism and geotropism in plants.  

 

Theory

Phototropism

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 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 farthest from the light. This hormone reacts to produce more protein and generates energy for the plant. This causes the plant to have elongated cells on the farthest side from the light. Almost all plants respond to photosynthesis to get more nutrition and energy. Phototropism can be demonstrated by using an apparatus like a heliotropic chamber.  

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. 

Phototropism 

 

Geotropism 

Geotropism is the movement or growth of plant parts in response to the force of gravity. The plant's stems show negative geotropism, while the roots show positive. Positive geotropism is the movement of plant parts toward gravitational attraction. In contrast, 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 grows less, which causes the root to grow downward or in the direction of gravity. Also, the auxin inhibits the growth at the bottom and promotes the growth at the top. The factors responsible for the geotropic modifications are root, shoot apices, humidity, and temperature. 

Geotropism 


 

Learning outcomes 

Students should be able to: 

  • Understand that phototropism causes plant stems to bend toward a light source (positive phototropism) or away from it (negative phototropism).
  • Understand that geotropism causes plant roots to grow downward (positive geotropism) and stems to grow upward (negative geotropism) relative to the force of gravity.
  • Understand and conduct accurate experiments to show the phenomenon of phototropism and geotropism in plants.