What type of structural units make up the construction of friction ridges?

Friction ridges, which create fingerprints, are primarily composed of ridge units. These units are the fundamental building blocks responsible for the unique patterns found in fingerprints. Each ridge unit consists of a series of raised lines or ridges that run parallel to one another, forming distinct patterns that can be classified into loops, whorls, and arches.

Ridge units are crucial for the tactile perception that humans experience, allowing for enhanced grip and friction when interacting with surfaces. The formation of these ridges occurs during fetal development, driven by genetic and environmental factors, and remains consistent throughout an individual's life, making them invaluable for identification purposes in forensic science.

The other choices do not accurately represent the structural components of friction ridges. Cell clusters refer to groups of cells and are not specifically related to the structure of friction ridges. Stratum layers pertain to skin layers but do not denote the basic units of friction ridge formation. Follicle strands are associated with hair follicles and also do not relate to the structure of fingerprints. Thus, ridge units are the correct answer as they directly describe the composition of friction ridges in fingerprints.