IGNOU BBYCT 137 2026 - Explain the polymer trapping model for symplastic loading of phloem.

Question

Explain the polymer trapping model for symplastic loading of phloem.

31 Jan 2026

Answer :

Word Count : 240

The polymer trapping model is a mechanism explaining symplastic phloem loading in certain plants, particularly those with minor veins adapted for efficient sugar transport. In this model, sucrose synthesized in mesophyll cells diffuses into specialized companion cells called intermediary cells through plasmodesmata, which are cytoplasmic channels connecting cells. The key feature of the polymer trapping model is the selective retention of larger oligosaccharides within the phloem, which drives a concentration gradient that facilitates continuous sucrose movement. Once sucrose enters the intermediary cells, it is enzymatically converted into larger sugars

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