The key difference between phototropism and geotropism is that the phototropism is the response of plants towards or away from the sunlight whereas, geotropism is the response of plants towards or away from the gravitational force.
Animals can move, but plants cannot. Then how they respond to the environmental signals? That’s because though they can’t move, they too respond to stimuli in order to survive in the environment. The response of plants to the environmental stimuli is known as ‘Tropism’. Plants are able to respond towards the stimulus or away from the stimulus. They basically need to grow towards light and water to survive. Based on the type of the stimulus and the direction of the stimulus, there are different categories of tropism. When a plant turns towards the stimulus, we call it as positive tropism and the opposite; away from the stimulus is negative tropism. The main tropism types are phototropism, geotropism and thigmatropism.
1. Overview and Key Difference
2. What is Phototropism
3. What is Geotropism
4. Similarities Between Phototropism and Geotropism
5. Side by Side Comparison – Phototropism vs Geotropism in Tabular Form
What is Phototropism?
Why do plants grow towards the sunlight? That is because plants need sunlight for the process called photosynthesis. They convert the energy of light into carbohydrates (foods). Therefore they should get an ample amount of sunlight during the daytime. Hence, they bend, grow or turn towards the sunlight. Phototropism is this phenomenon. In other words, phototropism is the response of plants to the direction of sunlight. It is easy to understand this concept by a small experiment. When you keep a plant pot near the window, what will happen? Plants bend towards the sunlight and grow as shown in figure 01.
Based on the direction of the response (away or towards the sunlight) there are two types of phototropism namely negative phototropism and positive phototropism respectively. Plant stems show positive phototropism while roots show negative phototropism.
What is Geotropism?
The word ‘Geo’ refers to the Earth. Then the geotropism is the response of plants to the gravity. In other words, geotropism is the movements of plants or plant parts towards or away from the earth.
Similar to phototropism, geotropism is also of two types; they are negative geotropism and positive geotropism. When turning away from the gravitational force, it is negative geotropism while when moving towards the gravitational force, it is positive geotropism. Root tips show positive geotropisms because they grow towards the gravity or earth finding more nutrients and moisture. Stem tips show negative geotropism as they grow away from the gravity.
What are the Similarities Between Phototropism and Geotropism?
- Phototropism and geotropism are two types of plant responses to the stimuli.
- Both types have negative and positive movements.
- These movements are important for the plant survival.
What is the Difference Between Phototropism and Geotropism?
When a plant responds to sunlight, we call it as phototropism, and when a plant responds to gravity, we call it as geotropism. Both types have two modes namely negative and positive based on the direction of movement; away or towards respectively. The below infographic presents the difference between phototropism and geotropism in tabular form.
Summary – Phototropism vs Geotropism
Phototropism and geotropism are two tropisms shown by plants. The stimulus is sunlight in phototropism while gravity is the stimulus in geotropism. If a plant grows towards the sunlight, it is positive phototropism while the opposite is negative phototropism. Similarly, if a plant part turns towards the gravity, it is positive geotropism while the opposite is negative geotropism. Plant stems show positive phototropism and negative geotropism. Roots show positive geotropism and negative phototropism. This is the difference between phototropism and geotropism.
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