Stems move towards light and roots move towards the center of gravity due to their specialized growth responses influenced by environmental cues. These movements are guided by specific plant hormones and internal signals. Here's why stems and roots exhibit these growth patterns:

Stems Move Towards Light (Phototropism):

1. Auxin Redistribution: Stems contain a plant hormone called auxin, which plays a crucial role in phototropism. When light strikes the stem, it causes auxin to redistribute towards the shaded side.

2. Differential Growth: The auxin accumulation on the shaded side stimulates cell elongation, causing the cells on that side to grow more rapidly than the cells on the lighted side. This differential growth results in the bending of the stem towards the light source.

Roots Move Towards Center of Gravity (Geotropism):

1. Gravitropism Hormone: Roots respond to gravity due to the presence of a plant hormone called gravitropin or statoliths. Statocytes, specialized cells in the root cap, contain starch-filled organelles called amyloplasts that function as gravity sensors.

2. Amyloplast Sedimentation: When the plant is in an upright position, the amyloplasts settle down due to gravity. Their sedimentation is sensed by the statocytes, which trigger a series of physiological responses.

3. Hormonal Response: The gravitational stimulus leads to the redistribution of auxin, similar to phototropism. Auxin accumulates on the lower side of the root, promoting cell elongation in that region and causing the root to grow downward.

4. Root Cap Function: The root cap protects the root meristem and plays a vital role in geotropism. It ensures that the root tip continuously senses the direction of gravity and adjusts the growth accordingly.

These tropic responses are essential for plant survival and adaptation. Stems growing towards light ensure efficient photosynthesis, while roots growing towards the earth's center allow for anchoring, water, and nutrient uptake from the soil.