Final answer:
The life cycle with both haploid and diploid multicellular stages is the alternation of generations, which is haplodiplontic and found in plants.
Step-by-step explanation:
The type of life cycle that has both a haploid and diploid multicellular stage is known as alternation of generations. This life cycle, which is characteristic of plants, is described as haplodiplontic. In this cycle, the haploid multicellular form, known as a gametophyte, produces gametes by mitosis, which then fuse to form a diploid zygote. This zygote develops into a multicellular diploid form called the sporophyte. The sporophyte produces spores by meiosis, which then develop into new gametophytes, completing the cycle.
Alternation of generations describes a life cycle in which an organism has both haploid and diploid multicellular stages. This type of life cycle, which is found in all plants, is described as haplodiplontic.