Final answer:
d) trichorrhexis nodosa
The hair condition caused by a defect in the hair's keratin protein structure is trichorrhexis nodosa. It leads to weak points in the hair fibers, causing brittleness and breakage. Dietary protein is crucial as it supports the ongoing cycle of hair growth.
Step-by-step explanation:
The hair problem that may be caused by an inherited defect in the hair's keratin protein structure is trichorrhexis nodosa. This condition is characterized by weak points or nodes along the hair shaft, where it becomes brittle and breaks easily. Hair keratin is a protein that provides strength and structure to hair, and a defect in this protein can lead to disruptions in the integrity of hair fibers. Such a structural anomaly in the hair can be a result of a hereditary condition affecting the production or composition of keratin in the hair follicle. Other problems like alopecia, trichonodosis, and plica polonica are related to different mechanisms and do not directly involve keratin protein structure defects.
Moreover, when considering the importance of dietary proteins, one must note that a lack of protein in the diet can lead to hair loss. This occurs because the body, which prioritizes the use of protein for critical functions, will reduce the allocation of proteins for hair growth during times of protein deficiency - underscoring the vital role of proteins in maintaining healthy hair growth.