Final answer:
The fibroblast cell type produces the ground substance in connective tissue.
Step-by-step explanation:
The connective tissue cell type that produces the ground substance in connective tissue is the fibroblast.
Fibroblasts are the most abundant cell type in connective tissue proper. They secrete polysaccharides and proteins that combine with extracellular fluids to produce a viscous ground substance.
This ground substance, along with embedded fibrous proteins, forms the extracellular matrix of connective tissue.