Final answer:
Fungi predominantly live in a haploid state throughout their life cycle, with a brief diploid phase occurring during sexual reproduction when a zygote is formed and quickly undergoes meiosis to return to the haploid state.
Step-by-step explanation:
Fungi live most of their life cycle as haploid organisms. The haploid-dominant life cycle characterizes most fungi and some algae, meaning the multicellular body of these organisms primarily exists in the haploid state. These haploid cells form the tissues of the multicellular stage and are produced by mitosis.
During sexual reproduction, specialized haploid cells from two different mating types, designated as (+) and (-), fuse to form a diploid zygote. However, this diploid state is transient as the zygote immediately undergoes meiosis to produce haploid spores. These spores contain a new combination of genetics from both parents and can stay dormant until conditions are favorable, at which point they germinate and grow into a new multicellular haploid organism through mitosis.