How do gymnosperms synthesize?

they are seed plants

Gymnosperms are any of a group of vascular plants that produce naked seeds (not enclosed in an ovary or fruit). They were formerly considered a class (Gymnospermae) of seed plants, but are now...

Gymnosperm means naked cell

No a gymnosperm is not a cone the cone is the reproductive structure of a gymnosperm

Gymnosperm are plant and therefore subsist from nutrients from the soil and produce their own 'food' via photosynthesis.