Question

why are the underground parts of the plants like radish carrot beet and sweet potato thick fleshy and swollen and which parts of the plant are they
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Answer 1

Answer:

those plants parts contain food storage so they swell up and parts are roots.

HOPE THIS HELP

Answer 2

These plants mostly bi-annuals. So, 1st year they store food(as starch) in their roots, which then gets swollen.

In winter, upper part (leaves) dies, but the plant survive and storage food gives boost for new growth in spring (2nd year). Then, it gives leaves and flower.

They are all roots, only sweet potatoes are adventitious root, all other tap root (modified to store food).

In some plants, the roots become fleshy due to the absorption of food material. The aerial parts of these plants worn out due to unfavorable conditions. When the conditions are favorable again new buds emerge either from the fleshy root or from a small bit of stem above. For eg., the taproots of carrot and turnip get swollen to store food.

A geophyte (earth+plant) is a plant with an underground storage organ including true bulbs, corms, tubers, tuberous roots, enlarged hypocotyls, and rhizomes. Most plants with underground stems are geophytes but not all plants that are geophytes have underground stems. Geophytes are often physiologically active even when they lack leaves.

Hope this helps :D