General Biology I

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Indole-3-acetic acid

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General Biology I

Definition

Indole-3-acetic acid (IAA) is a naturally occurring plant hormone that plays a crucial role in regulating various aspects of plant growth and development, particularly in cell elongation, root formation, and response to light and gravity. It is classified as an auxin, which are hormones involved in coordinating many growth processes in plants, affecting how they respond to their environment.

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5 Must Know Facts For Your Next Test

  1. Indole-3-acetic acid is produced in the shoot apical meristem and young leaves, where it is synthesized from tryptophan, an amino acid.
  2. IAA affects cell elongation by promoting the loosening of cell walls, allowing cells to expand more easily.
  3. This hormone is key in establishing apical dominance, where the main central stem grows more robustly than side stems, influencing overall plant shape.
  4. IAA levels can be altered by environmental factors such as light and gravity, leading to adaptations like bending toward light or growing roots downward.
  5. In addition to its growth-regulating functions, indole-3-acetic acid is involved in processes such as fruit development and the formation of lateral roots.

Review Questions

  • How does indole-3-acetic acid influence plant growth and development?
    • Indole-3-acetic acid influences plant growth by regulating processes such as cell elongation, root formation, and overall plant architecture. It promotes elongation in cells by loosening their walls, which allows them to expand. This hormone also helps establish apical dominance, ensuring that the main stem grows stronger than lateral branches. Additionally, IAA is involved in responses to environmental cues like light and gravity.
  • Discuss the role of indole-3-acetic acid in phototropism and how it affects plant behavior.
    • Indole-3-acetic acid plays a vital role in phototropism by redistributing unevenly within a plant when it is exposed to light from one direction. The side of the plant that receives less light accumulates more IAA, causing those cells to elongate more than those on the light-exposed side. This differential growth causes the plant to bend toward the light source, optimizing its ability to capture sunlight for photosynthesis.
  • Evaluate the significance of indole-3-acetic acid's effects on gravitropism in terms of plant survival and adaptation.
    • Indole-3-acetic acid's effects on gravitropism are crucial for a plant's ability to orient itself properly in relation to gravitational pull. When roots sense gravity, IAA redistributes within the root tips; typically causing the lower side to have higher concentrations which leads to differential growth. This allows roots to grow downward into the soil for stability and nutrient acquisition while stems grow upward toward light. Such responses enhance a plant's survival by ensuring it can effectively access necessary resources from its environment.

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