Final answer:
The component of hair allowing moisture or chemicals to reach the cortex is the b) Cuticle. It serves as a protective barrier and its condition affects hair's health and how it interacts with substances.
Step-by-step explanation:
The component of hair that gives moisture or chemicals access to the cortex, with the degree of access depending on the cuticle's qualities, is b) Cuticle. The cuticle is the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb. This structure serves as a protective barrier for the inner layers of the hair, namely the cortex and the medulla. The condition of the cuticle affects hair's overall health and porosity, influencing how substances like water and chemical treatments interact with the hair.
Furthermore, the hair shaft has three zones: the cuticle, the cortex, and the medulla. The cortex makes up the middle zone and is the main structure that influences hair texture, such as whether the hair is straight or curly. The hair matrix contains a layer of basal cells which are crucial in the process of hair growth and keratinization. The part of the hair above the skin is composed of dead, keratinized cells that make up the hair shaft.