Which of the following plant responses requires the integration of auxin?

• A. Formation of lignin in cell walls
• B. Stomatal closure during drought
• C. Phototropism
• D. Production of phytoalexins

Answer: (C)

Verified step by step guidance

1. Understand the role of auxin: Auxin is a plant hormone that plays a critical role in regulating growth and development, particularly in processes like cell elongation, apical dominance, and responses to light and gravity.
2. Define phototropism: Phototropism is the growth of a plant in response to light direction. Plants bend toward light to optimize photosynthesis, and auxin is key to this process.
3. Explain auxin's mechanism in phototropism: Auxin redistributes to the shaded side of the plant stem, promoting cell elongation on that side. This differential growth causes the plant to bend toward the light source.
4. Compare phototropism with other options: Formation of lignin in cell walls, stomatal closure during drought, and production of phytoalexins are processes that do not primarily involve auxin. For example, lignin formation is related to structural support, stomatal closure is regulated by abscisic acid, and phytoalexins are antimicrobial compounds produced during pathogen attack.
5. Conclude that phototropism is the correct answer: Based on the role of auxin in light response and cell elongation, phototropism is the plant response that requires the integration of auxin.