Xylem and Phloem: The Two Transport Systems in Flowering Plants | 木质部与韧皮部：开花植物的两大运输系统

📚 Xylem and Phloem: The Two Transport Systems in Flowering Plants | 木质部与韧皮部：开花植物的两大运输系统

Plants need to move water, mineral ions and organic assimilates over long distances between roots, stems and leaves. The xylem and phloem are the two transport systems that make this possible. Xylem mainly carries water and dissolved minerals from the roots upward, while phloem carries sugars and other organic products from sources to sinks.

植物需要将水、矿物质离子和有机同化产物在根、茎、叶之间进行长距离运输。木质部和韧皮部就是实现这一功能的两大运输系统。木质部主要负责将水和溶解的矿物质从根部向上运输，韧皮部则将糖类及其他有机产物从源运输到库。

1. Why Plants Need Two Transport Systems | 为什么植物需要两套运输系统

Diffusion is only effective over very short distances. A leaf can be several metres above the root, and storage organs may be far from photosynthetic tissues. Therefore plants need mass transport systems to move water, minerals and assimilates rapidly through specialised tubes.

扩散只在很短的距离内有效。叶片可能位于根部上方数米处，贮存器官也可能远离光合组织。因此植物需要集流运输系统，通过特化的管状结构快速运输水、矿物质和同化产物。

Xylem transport is essentially unidirectional, from roots to shoots. Phloem transport is bidirectional, moving assimilates from source to sink depending on the plant’s needs and stage of development.

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