What is the Difference Between Heliotropism and Phototropism

The main difference between heliotropism and phototropism is that heliotropism is the movement of plants in response to sunlight during daytime, whereas phototropism is the growth of plants towards sunlight.  

Heliotropism and phototropism are two responses of plants to sunlight. Plants grow and turn towards the sun in both types of movements. 

Key Areas Covered

1. What is Heliotropism
– Definition, Facts, Examples
2. What is Phototropism
– Definition, Facts, Types, Examples
3. Similarities Between Heliotropism and Phototropism
– Outline of Common Features
4. Difference Between Heliotropism and Phototropism
– Comparison of Key Differences

Key Terms  

Heliotropism, Phototropism, Positive Phototropism, Negative Phototropism

What is Heliotropism

Heliotropism, or solar tracking, is the movement of plants following the sun’s movement during the daytime. ‘Helio’ in Greek refers to the sun. Therefore, heliotropism is the movement of living organisms in response to the sun. In plants, heliotropism occurs in plant parts. The turning of the flower of sunflower occurs due to heliotropism. Also, the scientific name of the sunflower is Helianthus annuus. These flowers track the sun’s motion across the sky from east to west. Daisies or Bellis perennis open their petals for the morning light and follow the sun. Also, it closes their petals at night. Flowers assume a random orientation during the night. However, at dawn, flowers again turn to the east.

Figure 2: Heliotropism

Furthermore, the motor cells perform the motion of flowers. Flowers contain a flexible segment just below the flower, and it is called a pulvinus. The motor cells in the flexible segment pump potassium ions into nearby tissues. It changes their turgor pressure. The shadow side elongates due to the increase in turgor pressure.   

What is Phototropism 

Phototropism is the growth of a part of a plant in response to the direction of the light. Generally, the hormone responsible for the growth is auxin. It regulates the elongation of the newly differentiated cells at the tips of both stem and root. Moreover, there are two types of phototropism based on the direction of the elongation in response to light. They are positive and negative phototropism. 

Positive Phototropism 

Positive phototropism occurs in the apex of the stem. Generally, it is responsible for the growth of the stem apex towards the light. However, when the plant receives directional sunlight, auxin in the apical meristem tends to gather in the shaded side, resulting in the higher elongation of cells in the shaded side compared to the bedazzling side. In turn, it bends the stem’s tip towards the light source.

Figure 1: Phototropism

Negative Phototropism  

The apex of the root shows negative phototropism as it grows away from the light source. Normally, this is due to the concentration of auxin at the bottom of the root, elongating cells in the apex into the soil.

Similarities Between Heliotropism and Phototropism

• Heliotropism and phototropism are two responses of plants to sunlight.
• Plants grow towards the sunlight. 

Difference Between Heliotropism and Phototropism

Definition

Heliotropism refers to the directional growth of a plant in response to sunlight. In contrast, phototropism refers to the orientation of living organisms in response to light, either towards the light source (positive phototropism) or away from it (negative phototropism).

Type of Growth

Heliotropism is the movement of plants in response to sunlight in the daytime, while phototropism is the growth of plants towards the sunlight. 

Examples

Young sunflower plants following the sun are an example of heliotropism, while plants growing opposite to the sunlight are an example of phototropism. 

Conclusion

In brief, heliotropism and phototropism are two movements of plants in response to sunlight. Heliotropism is the directional movement of plants in response to the sunlight in the daytime. Young sunflower plants following the sun is an example of heliotropism. In comparison, phototropism is the growth of plants in response to sunlight. Also, it can occur either towards the source of light, positive or negative phototropism, which can occur away from it. Plants growing towards the sunlight are an example of phototropism. Therefore, the main difference between heliotropism and phototropism is their type of response to the sunlight.     

References:

1. Editors, B. (2017, April 29). Phototropism – definition, examples and quiz. Biology Dictionary. 
2. What is heliotropism?. Extension. (2021, June 1). 

Image Courtesy:

1. “Phototropism” By Tangopaso – Own Work (CC-BY SA 3.0) via Commons Wikimedia
2. “A Gaenseblume4” By böhringer friedrich – Own work (CC-BY SA 2.5) via Commons Wikimedia