Question

how stem different from stem tuber

Answer 1

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━━━━━━━━━━━━━━━━━━━$\mathfrak{\green{Answer.}}$Stem tubers. A stem tuber forms from thickened rhizomes or stolons. The top sides of the tuber produce shoots that grow into typical stems and leaves and the under sides produce roots. They tend to form at the sides of the parent plant and are most often located near the soil surface.
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Answer 2

Tubers are enlarged structures in some plantspecies used as storage organs for nutrients. They are used for the plant's perennation(survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and as a means of asexual reproduction.[1] Stem tubersform from thickened rhizomes (underground stems) or stolons (horizontal connections between organisms). Common plant species with stem tubers include potato and yam. Some sources also treat modified lateral roots(root tubers) under the definition; these are encountered in sweet potato, cassava, and dahlia.

Stem :

A stem is one of two main structural axes of a vascular plant, the other being the root. The stem is normally divided into nodes and internodes:

The nodes hold one or more leaves, as well as buds which can grow into branches (with leaves, conifer cones, or inflorescences(flowers)). Adventitious roots may also be produced from the nodes.The internodes distance one node from another.

The term "shoots" is often confused with "stems"; "shoots" generally refers to new fresh plant growth including both stems and other structures like leaves or flowers. In most plants stems are located above the soil surface but some plants have underground stems.

Stems have four main functions which are:[1]

Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.Transport of fluids between the roots and the shoots in the xylem and phloemStorage of nutrientsProduction of new living tissue. The normal lifespan of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.

hope it helps you friend.

@ sk