I sounds like your normals need to be inverted. The render by default only renders the side with the positive normal.
If so, you have two options.
Select single or multiple objects in question and then press Model-Effects/ Invert.
If you will need to see both sides (ex: an insect wing), then you can tell the renderer to render boths sides by turning off "Back Culling" in your render options.
Note1: You can view your normals by selecting Show/Normals. Blue lines will display indicating the side that will be lit.
Note2: You can usually tell when an object needs it's normals inverted in a shaded view, because it seems to be lit backwards (ie: light side is dark and dark side is light).
Note3: If you are using Preferences/ModelingRelations to make a surface associated to the curves use to construct it and the normals need inverting. Don't invert the surface, invert one of the curves that were used to create it. If you invert the surface, it will return to it's original state the next time the curves are modified.
Hope this helps
Urp