What is the Difference Between Positive and Negative Tropism

The main difference between positive and negative tropism is that positive tropism is the growth of a part of an organism towards a particular stimulus whereas negative tropism is the growth away from the stimulus. Furthermore, the growth of a root of a plant towards the gravity is an example of positive tropism while the growth of a shoot away from the gravity is an example of negative tropism.

Positive and negative tropism are two types of tropism, turning responses of living organisms. Especially, plants and fungi undergo tropism.

Key Areas Covered

1. What is Positive Tropism
     – Definition, Mechanism, Examples
2. What is Negative Tropism
     – Definition, Mechanism, Examples
3. What are the Similarities Between Positive and Negative Tropism
     – Outline of Common Features
4. What is the Difference Between Positive and Negative Tropism
     – Comparison of Key Differences

Key Terms

Auxin, Gravitropism, Negative Tropism, Phototropism, Positive Tropism, Stimulus, Turning responses

What is Positive Tropism

Positive tropism is a turning response or growth of an organism, especially a plant, towards a particular stimulus. Auxin is the plant hormone responsible for the directional movement of plants. Both shoot and root of a plant produce auxin at the tip. The main function of auxin is to regulate the rate of elongation. The growth of the shoot of a plant towards the light or phototropism is an example of positive tropism.

Figure 1: Phototropism

When the plant receives directional sunlight, auxin tends to gather in the shaded side in the tip of the shoot. Therefore, the cells in the shaded side elongate more under the influence of auxin, bending the tip of the shoot towards the light source.

What is Negative Tropism

Negative tropism is the growth of an organism away from a particular stimulus. Gravitropism is a common example which can be used to describe negative tropism. Generally, the shoot of the plant grows against gravity, which is a form of negative gravitropism. Here also, auxin is the plant hormone responsible for gravitropism.

Figure 2: Gravitropism

This hormone tends to gather in high concentrations at the bottom side of the horizontal stem, resulting in the higher elongation of cells in the bottom side. It causes the stem to bend upright. Gravitropism allows the shoot to grow in height, facilitating to obtain more sunlight.

Similarities Between Positive and Negative Tropism

• Positive and negative tropism are two types of tropism, a type of turning responses of living organisms.
• Only a part of the organism is involved in tropism.
• They allow organisms for better survival.
• Also, both mainly occur in plants and auxin is the plant hormone responsible for the directional growth of plants.
• Phototropism, gravitropism, thigmotropism, hydrotropism, thermotropism, and chemotropism are some of the types of tropism, which can be either positive or negative.

Difference Between Positive and Negative Tropism

Definition

Positive tropism refers to the growth in direction of a stimulus while negative tropism refers to the growth away from a stimulus. Thus, this is the main difference between positive and negative tropism.

Stem

The stem of the plant shows positive phototropism and negative geotropism.

Root

Also, another difference between positive and negative tropism is that the root of the plant shows positive geotropism while negative phototropism occurs in the root.

Conclusion

Positive tropism is the growth or a turning response of an organism towards the stimulus. In contrast, negative tropism is the growth of the organism away from the stimulus. Both types of tropism help organisms for better survival. However, the main difference between positive and negative tropism is the direction of turning with respect to the stimulus.

References:

1. Bailey, Regina. “How Plants Respond to Light, Touch, and Other Stimuli.” Thoughtco., Dotdash, 28 Feb. 2018, Available Here.

Image Courtesy:

1. “Phototropism Diagram” By MacKhayman – Own work (CC BY-SA 3.0) via Commons Wikimedia  
2. “Villa Gesell Casa del Árbol 01” By Roberto Fiadone – Own work (CC BY-SA 4.0) via Commons Wikimedia