Which structure protects the plant body against the invasion of parasites?

$(a)$ Why do sclerenchyma cells have a narrow lumen?
$(b)$ Where are these tissues present and why?

State whether the following statement is true or false:
The cells of collenchyma are living,elongated,and irregularly thickened at the corners.

Give the location and functions of the following tissues:
$(a)$ Cartilage
$(b)$ Areolar tissue
$(c)$ Adipose tissue

Name the type of parenchyma tissue present in aquatic plants. State its role.

Nervous tissue is not found in