The organelle that functions as a storage tank for excess glucose or starch in plant cells is the amyloplast.

Here's why:

* Amyloplasts are specialized plastids that are responsible for storing starch.

* Chloroplasts are the organelles where photosynthesis occurs, producing glucose.

* When a plant produces more glucose than it needs immediately, the excess glucose is converted into starch and stored in the amyloplasts.

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