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GCSE Biology

Why does the phloem have sieve plates when it could be like the xylem and be made up of long empty cells forming an empty tube structure.
Phloem contains specialized cell types. Sieve elements are long cells with restricted protoplasm and end walls penetrated by large pores. They are arranged vertically in series to form sieve tubes that allow the movement of water and assimilates with low resistance.

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