The Question is from neet-botany , and it was created by the author Mr. NARESH KUMAR K

Question

A mutant plant exhibits stunted root growth and reduced gravitropic response. Microscopic analysis reveals disorganized columella cells in the root cap. Which of the following is the MOST likely cause of this phenotype?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Plant gravitropism and root development
 **Related Topics**: Root cap structure, columella cells, amyloplasts, auxin, gravitropic response
 **Prerequisites**: Understanding of plant cell structure, plant hormones, and the role of amyloplasts in gravitropism.
## SOLUTION PATHWAY
**Given Information**:
  Stunted root growth, reduced gravitropic response, disorganized columella cells.
  Columella cells are crucial for gravitropism.
**Method & Steps**:
 1. Analyze the role of columella cells in gravitropism.
  Reasoning: Columella cells in the root cap contain statoliths (amyloplasts) that sediment in response to gravity. This sedimentation triggers auxin redistribution, leading to differential cell elongation and the gravitropic bending of the root.
  Formula/Rule:  No specific formula is applicable here, the understanding of the process is key.
 2. Consider the effect of disorganized columella cells.
  Working: Disorganized columella cells would disrupt the sedimentation of amyloplasts, preventing proper auxin redistribution.
  Key Point:  Auxin is essential for root growth and gravitropic response.  Its asymmetric distribution is key.
 3. Evaluate the options based on the disrupted amyloplast sedimentation and auxin redistribution.
  Result: Option B directly addresses the disrupted amyloplast sedimentation and auxin redistribution, which is the most likely cause of the observed phenotype.
  Verification: The other options are less likely. Increased cytokinin would promote growth (not stunted growth). Overexpression of cell elongation genes wouldn't explain the disorganized columella cells or reduced gravitropism. Enhanced ethylene sensitivity is not directly linked to columella cell organization or gravitropism.
 ## OPTION ANALYSIS
A :x: Increased production of cytokinin in the root tip would likely promote, not inhibit, root growth.
B ✓: Disruption of amyloplast sedimentation and auxin redistribution directly explains the disorganized columella cells and the reduced gravitropic response.
 C :x: Overexpression of genes involved in cell elongation would likely lead to increased, not stunted, growth.
D :x: Enhanced sensitivity to ethylene is not the primary cause of disorganized columella cells and reduced gravitropism.
 ## LEARNING AIDS
 **Common Mistakes**:
  1. Focusing on individual symptoms without considering the interconnectedness of root growth and gravitropism: Understanding the role of amyloplasts and auxin is crucial for a correct answer.
  2. Overlooking the significance of columella cells in gravitropism: Columella cells are the key players in sensing gravity and initiating the gravitropic response.
 **Quick Tips**:
  1. Remember the role of amyloplasts (statoliths) in gravity sensing and auxin redistribution in root gravitropism.
  2.  Associate disorganized columella cells with impaired gravity sensing and subsequent auxin redistribution.

Mr. NARESH KUMAR K · Answer

Increased production of cytokinin in the root tip

Mr. NARESH KUMAR K · Answer

The correct Option is "Disruption of amyloplast sedimentation and auxin redistribution"

Mr. NARESH KUMAR K · Answer

Overexpression of genes involved in cell elongation

Mr. NARESH KUMAR K · Answer

Enhanced sensitivity to ethylene

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