What is phototropism?

• A. Growth toward gravity
• B. Growth toward moisture
• C. Growth toward or away from light
• D. Growth toward nutrients

Answer: (C)

Phototropism is the directional growth of a plant in response to light. In shoots, light on one side causes the shaded side to accumulate more auxin, a growth hormone, which promotes cell elongation and makes the stem bend toward the light. This is why shoots exhibit positive phototropism—growing toward light. Roots, when exposed to light, often bend away, showing negative phototropism, though root growth is also strongly influenced by gravity. Phototropism is distinct from responses to gravity, moisture, or nutrients, which are gravitropism, hydrotropism, and chemotropism respectively.