Question

secondary growth can be explained as
change in the diameter via the cambium
change in length via the apical meristem
area where water & mineral absorption occurs, increases surface area of the root
process of water movement from the roots to the leaves where it evaporates

Explanation:

Secondary growth in plants is mainly due to the activity of lateral meristems like the vascular cambium. It leads to an increase in the girth (diameter) of the plant. The apical meristem is responsible for primary growth (increase in length). The area for water and mineral absorption (root hairs) is related to root function for uptake, and the process of water movement from roots to leaves (transpiration stream) is about water transport.

Answer:

Change in the diameter via the cambium