The Question is from neet-botany plant-growth-and-development , and it was created by the author K SURESH KUMAR

Question

A plant exposed to unidirectional light exhibits phototropism.  If the tip of the coleoptile is removed and replaced with a gelatin block, then illuminated from one side, which of the following will be observed?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Phototropism and the role of auxin in plant growth.
 **Related Topics**: Plant hormones, signal transduction, directional growth responses.
 **Prerequisites**: Understanding of phototropism as a directional growth response to light, and the role of the coleoptile tip in auxin production and transport.
## SOLUTION PATHWAY
**Given Information**:
  * A plant exhibits phototropism (bending towards a light source).
  * The coleoptile tip (the site of auxin production) is removed.
  * A gelatin block replaces the tip.
  * The plant is illuminated from one side.
**Method & Steps**:
 1. Understanding the role of the coleoptile tip: The tip of the coleoptile is responsible for detecting the light stimulus and producing the plant hormone auxin.  Auxin then diffuses down the coleoptile, causing differential cell elongation on the shaded side, leading to bending towards the light.
  Reasoning:  The gelatin block is inert and cannot produce or transport auxin.
  Formula/Rule: None directly applicable, this is a biological process explanation.
 2. Effect of gelatin block replacement: Since the gelatin block cannot replace the function of the coleoptile tip in auxin production and transport, the necessary signal for differential growth is absent.
  Working:  Without the auxin gradient, there is no differential cell elongation on the shaded side.
  Key Point: The experiment demonstrates that the coleoptile tip is crucial for the phototropic response.
 3. Observation: The coleoptile will not bend towards the light source because the mechanism for detecting light and initiating differential growth is disrupted.
  Result: The coleoptile will not bend towards the light source.
  Verification: This aligns with the known mechanism of phototropism and the role of auxin.
 ## OPTION ANALYSIS
A :x: The coleoptile cannot bend towards the light because the auxin production and transport mechanism is interrupted.
B :x:  There is no mechanism for bending away from the light source in this scenario.
C ✓: Correct. The removal of the coleoptile tip and its replacement with an inert gelatin block prevents the generation of the auxin gradient necessary for phototropism.
D :x: The coleoptile's growth will not be random; it will simply lack the directional bending due to the absence of auxin signaling.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming that the gelatin block can somehow mimic the function of the coleoptile tip: The gelatin block is a passive material and cannot participate in the complex biochemical processes involved in auxin production and transport.
  2.Overlooking the importance of the coleoptile tip in phototropism:  The experiment is designed to highlight the specific role of the coleoptile tip in mediating the phototropic response.
 **Quick Tips**:
  1.Remember that phototropism requires auxin production and differential cell elongation.
  2.Visualize the experiment: Imagine the setup and consider what would happen in the absence of auxin signaling.

K SURESH KUMAR · Answer

The coleoptile will bend towards the light source.

K SURESH KUMAR · Answer

The coleoptile will bend away from the light source.

K SURESH KUMAR · Answer

The correct Option is "The coleoptile will not bend towards the light source."

K SURESH KUMAR · Answer

The coleoptile will exhibit random growth.

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