What is the Difference Between Phototropism and Geotropism

The main difference between phototropism and geotropism is that phototropism is the growth of plants towards light whereas geotropism is the growth of plants towards gravity. Furthermore, the stem of plants shows positive phototropism while the root of the plant shows positive geotropism.

Phototropism and geotropism are two types of tropism, which indicates the growth or turning movement of a plant in response to an environmental stimulus. More importantly, auxin is the plant hormone responsible for the directional growth of plants.

Key Areas Covered

1. What is Phototropism
     – Definition, Mechanism, Importance
2. What is Geotropism
     – Definition, Mechanism, Importance
3. What are the Similarities Between Phototropism and Geotropism
     – Outline of Common Features
4. What is the Difference Between Phototropism and Geotropism
     – Comparison of Key Differences

Key Terms

Auxin, Geotropism, Gravity, Light, Phototropism, Root, Stem

What is Phototropism

Phototropism is the growth of a plant in response to light. Here, auxin is responsible for the directional growth of the parts of plants in response to light. It regulates the elongation of the newly differentiated cells at the tips of both stem and root. In the stem, phototropism is a type of positive tropism, involved in the growth of the stem towards the light. Generally, when a plant receives directional sunlight, auxin tends to gather in the shaded side in the tip of the stem. This results in the higher elongation of cells in the shaded side compared to the bedazzling side, which in turn bends the tip of the stem towards the light source.

Figure 1: Phototropism of the Stem

However, the root of the plant shows negative phototropism as it grows away from the light source. It is due to the concentration of auxin cells at the bottom side root, elongating those cells to grow into the soil.

What is Geotropism

Geotropism is the growth of a part of a plant in response to gravity. Auxin is the hormone responsible for geotropism as well. In the tip of the root, auxin concentrates at the bottom cells. It allows the cells at the tip of the root to elongate, growing the root into the soil, towards the gravity. Therefore, the root shows a type of positive geotropism.

Figure 2: Geotropism of the Root

However, the stem of the plant shows negative geotropism. Therefore, it grows away from gravity.

Similarities Between Phototropism and Geotropism

• Phototropism and geotropism are two types of growth which occur in plants.
• They are categorized under tropism.
• Also, both are responsible for the growth of all or a part of the plant in response to a particular stimulus.
• In both, positive and negative tropism can be identified.
• Furthermore, both types of tropism growth mechanisms ensure the survival of plants.
• Besides, auxin is responsible for both phototropism and geotropism.

Difference Between Phototropism and Geotropism

Definition

Phototropism refers to the orientation of a plant or other organism in response to light while geotropism refers to the growth of the parts of plants in response to the force of gravity. Thus, this is the main difference between phototropism and geotropism.

Stimulus

The stimulus involved in the phototropism is light while the stimulus involved in geotropism is gravity.

Positive Tropism

Another difference between phototropism and geotropism is that the stem of the plant shows positive phototropism while the root of the plant shows positive geotropism.

Negative Tropism

Moreover, the root of the plant shows negative phototropism while the stem of the plant shows negative geotropism. Hence, this is another difference between phototropism and geotropism.

Importance

Besides, one other difference between phototropism and geotropism is that the phototropism allows plants to obtain more light as required by photosynthesis while geotropism allows the plant to search for more water and nutrient sources.

Conclusion

Phototropism is the growth of the part of a plant in response to light. Here, the stem of the plant grows towards the light, showing positive phototropism, while the toot of the plant shows negative phototropism by growing away from the light. Therefore, phototropism allows the shoot to obtain more light for photosynthesis. In contrast, geotropism is the growth of plants in response to gravity. Here, the root of the plant grows towards the gravity, showing positive geotropism, while the stem of the plant grows away from the gravity, showing negative geotropism. Therefore, geotropism allows the root of the plant to achieve more water and nutrient sources. Hence, the main difference between phototropism and geotropism is the type of stimulus and importance.

References:

1. Weber, Danielle. “Tropisms: Phototropic, Geotropic and Thigmotropic Plant Growth.” Study.com, Study.com, Available Here.

Image Courtesy:

1. “IMG_3558” By rudy.kleysteuber (CC BY 2.0) via Flickr
2. “Ta Prohm sprung tree” By Jasoneppink – Own work (CC BY 2.0)  via Commons Wikimedia 

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