Final answer:
In bryophytes, rhizoids act as structures that fulfill a similar role to roots in vascular plants, by providing anchorage and aiding in nutrient absorption.
Step-by-step explanation:
The structures that replace roots in the Kingdom Bryophyta (bryophytes) are known as rhizoids. Unlike the robust root systems seen in vascular plants, rhizoids are thin, root-like filaments that attach bryophytes to their substrate. They are much less efficient at anchoring the plant and tend to absorb water and nutrients less effectively compared to the developed root systems equipped with vascular tissue. Therefore, the correct answer to the question is A) Rhizoids.