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Zorluk: OrtaHormonal Coordination in Plants and Animals

A seedling growing indoors near a window receives light predominantly from one side. Over several days, the shoot apex bends markedly toward the window. Which of the following best explains the movement and action of auxin in this phototropic response?

  1. Auxin migrates laterally from the illuminated side to the shaded side, promoting cell elongation on the shaded side.Cevap
  2. B
    Auxin accumulates on the illuminated side of the stem, accelerating cell division on the side facing the light.
  3. C
    Auxin is synthesized exclusively on the illuminated side, causing the sunlit tissues to expand faster.
  4. D
    Auxin is evenly distributed throughout the stem, but light directly inhibits growth on the shaded side.

Cevap

Auxin migrates laterally from the illuminated side to the shaded side, promoting cell elongation on the shaded side.
The correct response accurately states that unidirectional light causes auxin to migrate laterally to the shaded side of the stem tip. The resulting higher auxin concentration on the shaded side stimulates greater cell elongation compared to the illuminated side, forcing the stem to bend toward the light source.

Adım Adım Çözüm

1
Identify the environmental stimulus and plant hormone involved.
The stimulus is unilateral light (phototropism) and the primary regulatory hormone is auxin (indole-3-acetic acid).
Shoot bending in response to light is driven by hormonal redistribution.
2
Determine the direction of auxin lateral transport in the shoot apex.
Light perception at the tip triggers lateral movement of auxin from the illuminated side to the shaded side.
Photoreceptors (phototropins) induce asymmetrical transport of auxin carriers toward the shaded side.
3
Analyze the cellular effect of accumulated auxin on the shaded side.
Higher auxin concentration on the shaded side enhances cell wall loosening and cell elongation.
Differential elongation causes the shaded side to grow faster than the illuminated side, bending the stem toward the light.

Anahtar Kavram

Lateral transport of auxin in phototropism
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Konular

Hormonal Coordination in Plants and Animals

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