How are basal cells in stratified epithelia characterized and what is their location?

• A. Located at the base attached to the basement membrane; they are small, mitotically active progenitors for renewal.
• B. They are large superficial cells that form the protective barrier.
• C. They reside in the dermis producing collagen.
• D. They migrate to the surface to become keratinocytes.

Answer: (D)

Basal cells form the bottom, or basal, layer of stratified epithelia and are anchored to the basement membrane. They are small and mitotically active, acting as the renewing progenitors of the epithelium. Their daughters divide and then move upward through the layers, differentiating as they go until they become keratinocytes in the outermost layers. The key idea is that basal cells themselves stay at the base as progenitors, and their lineage migrates to the surface to form keratinocytes, which is why this description best fits their role and location.