This is the main structural axis of the plant that supports leaves, flowers and fruits; transports fluids; stores nutrients and produces new tissue.

Stem

Explanation:

Stem is considered to be one of the most important part of the whole plant when it comes to giving support to the other growing parts like flowers, fruits and leaves. There are inter-nodes and nodes present on the surface of stems. nodes are the points where inflorescence, other stems and more leaves are originated.They contain important transporting tissues Xylem and phloem inside that are involved in the transport of food and minerals to the growing parts of the plants.Stem also store nutrients in the form of sugars that can later be used for the growth and development of plant as well as for the production of more tissues.Though stems are above ground part of the plant but in some plants they can be underground too such as potatoes and ginger. However, underground stems also serve same role by supporting the overall structure of the plant.

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Covalent bond is the correct answer