what is a difference between primary metabolites and sedondary metabolites?

it seems that secondary metab serve no purpose for plant growth and development unlike primary metab. plants can survive without metab but cannot survive without primary metab

there are  3 types of secondary metaboliets

terpenes, phenolics, nitrogen containing compounds

types of terpenes

monoterpenes (2 C5 terpenes 10 carbon link)

sequiterpenes (3 C5 terpenes 15 carbon link)

diterpenes (4 C5 terpenes 20 carbon link)

Terpenes are biosynthesized from primary metabolites via 2 pathways?

Mevalonic  acid pathway 

methylerythritol phosphate pathway (MEP)