Phototropism:
Phototropism is the movement of plants in response to light. It is a phenomenon where the plant grows or bends towards a light source. This response occurs due to the influence of the hormone auxin, which is responsible for plant growth and development.

Mechanism of Phototropism:
1. Perception of Light: The first step in phototropism is the perception of light by the plant. This is done by a specialized pigment called phototropin, which is present in the plant cells.

2. Redistribution of Auxin: When light is perceived, auxin accumulates on the shaded side of the plant. This redistribution of auxin causes the cells on the shaded side to elongate and grow more rapidly than the cells on the illuminated side.

3. Bending Towards Light: As a result of differential cell elongation, the plant bends towards the light source, allowing the leaves to receive maximum light for photosynthesis.

Significance of Phototropism:
1. Maximizing Light Absorption: Phototropism allows plants to maximize their exposure to light, which is essential for photosynthesis. By bending towards light, plants can ensure that their leaves receive optimal light intensity for efficient photosynthesis.

2. Survival and Growth: Proper exposure to light is crucial for the survival and growth of plants. Phototropism helps plants in positioning their leaves and stems in such a way that they can capture maximum light energy for their metabolic processes.

3. Adaptation to Environment: Phototropism is a mechanism through which plants adapt to their environment. By growing towards light, plants can avoid being shaded by other plants and can compete for light resources more effectively.

4. Plant Orientation: Phototropism also influences the orientation of plants. For example, the upward growth of shoots and the downward growth of roots are also influenced by light. This helps plants in maintaining their proper orientation in response to gravity and light stimuli.

In conclusion, phototropism is a vital plant response to light that allows plants to optimize their growth, survival, and adaptation to their environment. The movement of the shoot towards light is a classic example of phototropism.