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

Question

The 'polymer trapping' model explains phloem loading by suggesting that sucrose is converted into larger molecules in which specific cell type?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Phloem loading and the polymer trapping model
 **Related Topics**: Sucrose transport, companion cells, sieve elements, phloem sap
 **Prerequisites**: Basic understanding of plant vascular tissues and carbohydrate metabolism.
## SOLUTION PATHWAY
**Given Information**:
  The question asks about the specific cell type where sucrose is converted into larger molecules according to the polymer trapping model of phloem loading.
  The options are: Sieve elements, Companion cells, Phloem parenchyma cells, Bundle sheath cells.
**Method & Steps**:
 1. Understand the polymer trapping model: This model proposes that sucrose is converted into larger molecules (like raffinose or stachyose) in the companion cells.
  Reasoning: The conversion of sucrose into larger molecules reduces the concentration of sucrose in the companion cells, maintaining a concentration gradient that facilitates the movement of sucrose from the mesophyll cells into the companion cells and subsequently into the sieve elements.
  Formula/Rule: No specific formula is applicable here.
 2. Analyze the options:  Consider the role of each cell type in phloem transport.
  Working: Sieve elements are primarily involved in the transport of phloem sap, but not the initial loading.  Phloem parenchyma cells and bundle sheath cells are not the primary sites for sucrose conversion in this model.
  Key Point: The key is understanding the role of companion cells in actively loading sucrose into the sieve tubes.
 3. Identify the correct cell type: Companion cells are the correct answer because they are metabolically active cells closely associated with sieve elements and are responsible for the active loading of sugars into the phloem.
  Result: Companion cells
  Verification: The polymer trapping model specifically points to the conversion of sucrose to larger molecules in companion cells to drive phloem loading.
 ## OPTION ANALYSIS
A :x: Sieve elements primarily transport the phloem sap, they don't actively load it.
B ✓: Companion cells are metabolically active and actively load sucrose into the sieve elements by converting it to larger molecules.
C :x: Phloem parenchyma cells have supporting roles but are not the primary site for this conversion.
D :x: Bundle sheath cells are associated with C4 photosynthesis and are not directly involved in phloem loading.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of sieve elements and companion cells: Remember that sieve elements are responsible for transport, while companion cells are responsible for active loading.
  2.Focusing on sucrose transport without considering the mechanism of loading: Understanding the polymer trapping model is crucial.
 **Quick Tips**:
  1.Remember that companion cells are metabolically active and closely associated with sieve elements.
  2.Associate the polymer trapping model with the conversion of sucrose into larger molecules in companion cells.

Mr. NARESH KUMAR K · Answer

Sieve elements

Mr. NARESH KUMAR K · Answer

The correct Option is "Companion cells"

Mr. NARESH KUMAR K · Answer

Phloem parenchyma cells

Mr. NARESH KUMAR K · Answer

Bundle sheath cells

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