What are the differences between positive and negative tropisms?

Positive tropism is the growth or movement towards a stimulus, while negative tropism is the growth or movement away from a stimulus.

Tropism is a biological phenomenon indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In the context of positive and negative tropisms, the direction of the organism's response is what differentiates the two.

Positive tropism is when an organism or a part of an organism moves towards the source of a stimulus. For example, phototropism is a type of positive tropism where plants grow towards the light. This is because light is a vital requirement for photosynthesis, the process by which plants produce their food. Similarly, geotropism or gravitropism is another example of positive tropism where roots of the plants grow downwards, towards the force of gravity, to anchor the plant and absorb water and nutrients from the soil.

On the other hand, negative tropism is when an organism or a part of an organism moves away from the source of a stimulus. For instance, in the case of negative phototropism, plant roots grow away from light. This is because exposure to light can lead to water loss and damage to the roots. Similarly, negative geotropism or gravitropism is observed in the upward growth of plant shoots, away from the force of gravity, enabling the plant to grow towards light and air.

In summary, the key difference between positive and negative tropisms lies in the direction of the organism's response to a stimulus. Positive tropism leads to movement towards the stimulus, while negative tropism results in movement away from it. Understanding these concepts is crucial in the study of plant behaviour and adaptation to their environment.