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

Question

A researcher is studying phloem transport in a plant using radioactive $^{32}P$. After introducing the radioisotope to a mature leaf, where would the LEAST radioactivity be detected after a short period?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Phloem transport and its dependence on plasmodesmata.
 **Related Topics**: Plant transport systems, radioisotope tracing, cell-to-cell communication in plants.
 **Prerequisites**: Understanding of phloem function (transport of sugars and other assimilates), the role of plasmodesmata in symplastic transport, and basic principles of radioisotope tracing.
## SOLUTION PATHWAY
**Given Information**:
  Radioactive $^{32}P$ is introduced to a mature leaf.
  Phloem transport is being studied.
  The question asks where the LEAST radioactivity would be found after a short time.
**Method & Steps**:
 1. Understand phloem transport: Phloem transports sugars and other assimilates from source (e.g., mature leaves) to sink (e.g., growing tissues, roots).
  Reasoning: The $^{32}P$ will be incorporated into these assimilates and transported via the phloem.
  Formula/Rule: No specific formula is needed for this qualitative question.
 2. Consider the role of plasmodesmata: Plasmodesmata are channels that connect adjacent plant cells, allowing for symplastic transport (movement through the cytoplasm).
  Working:  Phloem transport relies heavily on plasmodesmata for efficient movement of materials between cells.
  Key Point:  Areas lacking plasmodesmatal connections to the phloem will be less likely to receive the radioisotope.
 3. Identify the location with the least radioactivity:
  Result: Mature leaf cells lacking plasmodesmatal connections to the phloem will receive the least amount of $^{32}P$ because it cannot easily move into those cells via the phloem.
  Verification: The other options (apical meristem, young leaves, and roots) are all strong sinks for phloem transport and would thus show significant radioactivity after a short period.
 ## OPTION ANALYSIS
A :x: Apical meristems are actively growing tissues and strong sinks for phloem transport.
B :x: Young developing leaves are also strong sinks, requiring substantial resources transported via the phloem.
C :x: Roots are major sinks for phloem-transported sugars, receiving significant amounts.
D ✓: Mature leaf cells lacking plasmodesmatal connections to the phloem would be isolated from the phloem transport stream, thus receiving minimal $^{32}P$.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming all cells are equally connected to the phloem:  Understanding the importance of plasmodesmata in phloem transport is crucial.
  2.Overlooking the time constraint: The question specifies a short period, meaning only immediate transport routes are relevant.
 **Quick Tips**:
  1.Visualize the phloem as a network with plasmodesmata as connections; radioactivity follows this network.
  2.Remember that strong sinks receive the most transported materials.

Mr. NARESH KUMAR K · Answer

Apical meristem

Mr. NARESH KUMAR K · Answer

Young developing leaves

Mr. NARESH KUMAR K · Answer

Roots

Mr. NARESH KUMAR K · Answer

The correct Option is "Mature leaf cells lacking plasmodesmatal connections to the phloem"

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