Explain giving reasons the bending of the shoot tip of a plant towards light source coming from one side of the plant.

The bending of the shoot tip of a plant towards a light source is a phenomenon known as phototropism. Phototropism is the directional growth response of a plant in response to the direction of light. The bending occurs due to differential growth rates on the shaded and illuminated sides of the shoot tip.

Auxin Redistribution: Auxins are plant hormones that play a crucial role in the regulation of plant growth. When light strikes the shoot tip from one side, auxin redistributes to the shaded side of the shoot. This redistribution is a key factor in causing phototropism.

Cell Elongation: Auxin promotes cell elongation. As auxin accumulates on the shaded side of the shoot tip, it stimulates the cells on that side to elongate more rapidly than the cells on the illuminated side. This differential growth causes the shoot tip to bend towards the light source.

Cell Division: Auxin also influences cell division. While auxin promotes elongation in the shaded side, it inhibits cell division on that side. On the illuminated side, cell division is not inhibited. This difference in cell division further contributes to the bending of the shoot tip towards the light.

Gradient of Auxin: The asymmetrical distribution of auxin creates a concentration gradient across the shoot tip. This concentration gradient acts as a signal for directional growth, with higher concentrations of auxin on the shaded side guiding the bending of the shoot.

Receptor Sensitivity: The plant possesses light receptors, such as phototropins, that detect the direction of the light source. These receptors contribute to the polar transport of auxin towards the shaded side, further enhancing the asymmetrical auxin distribution and the subsequent bending response.

In summary, phototropism in plants is a complex process involving the redistribution of auxin, differential cell elongation and division, and the perception of light direction by specialized receptors. These responses collectively allow the plant to adjust its growth direction in response to the availability and direction of light, optimizing its exposure to sunlight for photosynthesis.