Final answer:
Keratin would not be found in significant amounts in the areolar connective tissue's extracellular matrix; this tissue mainly consists of proteoglycans and collagen.
Step-by-step explanation:
The substance that would NOT be found in significant amounts in the extracellular matrix of the illustrated areolar connective tissue is keratin. Areolar connective tissue primarily consists of a matrix that includes an amorphous ground substance made up of proteoglycans and fibrous proteins such as collagen and elastin. While collagen is the most abundant protein in the mammalian body and a vital component of the connective tissue matrix, providing structural support, keratin is a protein found mainly in epithelial cells, forming protective layers in structures such as skin, hair, and nails and would not typically be present in the connective tissue matrix.