What might you observe in plants exhibiting phototropism?

Observing plants that exhibit phototropism, you will notice that they grow toward the light source. This behavior is a response to the uneven distribution of auxins, which are plant hormones that promote cell elongation. When light shines on plant parts, typically the stem, it causes the auxins to concentrate on the side that is away from the light. As a result, the cells on the shaded side elongate more than those on the light-exposed side, leading to the bending of the plant toward the light. This adaptation allows plants to capture more sunlight for photosynthesis, enhancing their growth and survival.

The other choices do not accurately describe the phenomenon. While plants may grow sideways in some contexts, phototropism specifically refers to the growth towards light rather than sideways. Growing away from the light contradicts the very definition of phototropism, where plants seek light. Although a plant may develop a more robust stem as it adjusts to its environment, robust growth does not directly correlate with the light direction sought during phototropism. Thus, the distinctive growth pattern of bending toward the light source is the hallmark of phototropism.