How does young stem gives mechanical support to the plant body?

One is through turgidity. This occurs before ground tissue ( collenchyma and sclerenchyma cells) become well developed to give structural support to the plant as it grows bigger. The xylem tissue (composed of rigid tissue) of the young plant helps render this support and also maintaining osmotic turgidity of the surrounding plant cells.

is this a psat question, if so do not cheat try your best.

your answer is going to be physical weathering