Which concept explains the growth of plants toward light?

Phototropism is the concept that describes how plants grow toward light. This response is primarily facilitated by a plant hormone called auxin, which helps elongate cells on the side of the plant that is away from the light source, causing the plant to bend toward the light. This adaptation is crucial for maximizing photosynthesis, as increased exposure to light enhances a plant's ability to produce energy.

In contrast, gravitropism relates to how plants respond to gravity—roots generally grow downward (positive gravitropism), while stems typically grow upward (negative gravitropism). Thigmotropism involves growth responses to touch or physical contact, often seen in climbing plants or vines that wrap around supports. Kinesis refers to a non-directional response to stimuli, often seen in some organisms moving based on changes in their environment without a directed path.

Therefore, phototropism is specifically the response of growth toward light, making it the correct concept in this context.