bio question quick!

於考試, 回答時必須針對兩者的關係

Seive tube cells have end walls with many pores (sieve plate)
=> to enhance the trasport of organic nutrients from cell to cells
Seive tube cells have cytoplasm without nucleus
=> reduce the resistance to transport organic nutrients

Companion cells have both cytoplasm and nucleus
=> maintain the metabolic activities of sieve tube cells to trasport organic nutrients

Further information:
Carbohydrates transported through phloem is in the form of surcrose to minimize the osmotic effect.

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2012-04-21 09:51:42 補充：
篩管細胞
1. 有篩板於細胞的兩端
- 促進有機物的運輸
2. 有細胞質卻沒有細胞核
-減少運輸有機物時的阻力

伴細胞
-1. 有細胞質與細胞核
- 維持篩管細胞的代謝活動以運輸有機物

篩管分子之間細胞壁形成篩板,篩管分子旁邊有伴細胞,為篩管分子提供能量和控制分子內物質流動速度