Why do phloem and xylem not contain starch?

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SUMMARY

Phloem and xylem do not contain starch due to their distinct functions in plant physiology. Phloem is responsible for transporting sucrose, which is converted to starch in other parts of the plant, while xylem primarily transports water. Starch's low solubility in water makes it impractical for transport within these vascular tissues. Some plant species do store starch in underground stems and leaves, indicating that starch can be present in certain areas but is not transported through phloem or xylem.

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  • Familiarity with the solubility properties of starch and sugars
  • Basic botany concepts related to photosynthesis and storage products
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Botanists, plant physiologists, and students studying plant biology will benefit from this discussion, particularly those interested in plant transport systems and carbohydrate dynamics.

Lim Y K
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Why do phloem and xylem not contain starch?
 
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The phloem transports sucrose that is converted to starch elsewhere. The xylem transports mostly water.
 
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Looking at it from a different "why":

Starches are not very soluble in water, so dissolving and transporting them in water is not likely. Sugars like glucose and sucrose are soluble.

Actually this a great question. There are species that have starches in underground stems and some starch in the leaves. A priori, you would expect starch to be moved around in phloem in such a plant, at least, to account for getting the starch buildup in the underground stem, since starch is a storage product for photosynthetic sugars.
 
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