Question

In symplastic loading the transport sugars are mainly

• A. Sucrose
• B. Glucose
• C. Maltose
• D. Vitamin C

Hint:

Sucrose is the universal transport disaccharide in phloem translocation due to its non-reducing nature.
It is utilized in both apoplastic and symplastic loading pathways.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Phloem loading is the process by which photosynthetic products are transferred from mesophyll cells into the sieve elements of the phloem.
This loading occurs either through the apoplast (extracellular space) or the symplast (interconnected cytoplasm via plasmodesmata).

Step 3: Detailed Explanation:
Sucrose is the predominant and universal transport sugar in plants because of its chemical properties.
It is a non-reducing disaccharide, which makes it highly stable and less susceptible to enzymatic degradation during long-distance transport compared to reducing monosaccharides like glucose or fructose.
Even in species that use symplastic loading (often utilizing the polymer-trapping mechanism), sucrose is the initial sugar that enters the intermediary cells before being oligomerized into larger sugars like raffinose and stachyose.
Thus, sucrose remains the foundational transport sugar.

Step 4: Final Answer:
The transport sugar is mainly Sucrose, making option (A) correct.