Final answer:
Animals have a diploid-dominant life cycle, with the diploid stage being the main stage of existence, whereas plants have an alternation of generations, with both haploid (gametophyte) and diploid (sporophyte) multicellular stages.
Step-by-step explanation:
Animal and Plant Life Cycles
The main difference between the life cycles of animals and plants lies in the stages and dominance of haploid and diploid cells. In animals, the life cycle is typically diploid-dominant. This means that they spend the majority of their lifecycle as diploid organisms, with the haploid stage being only the gametes, such as sperm and eggs, which combine to form a diploid zygote. On the other hand, plants exhibit an alternation of generations that includes both haploid and diploid multicellular stages. In plants, diploid sporophytes produce haploid spores through meiosis, which then grow into multicellular haploid gametophytes. The gametophytes produce gametes through mitosis, which then fuse to form a diploid zygote, growing into the sporophyte, thus completing the cycle.
Animals do not undergo sporophyte and gametophyte stages as plants do. In contrast to haploid-dominant life cycles, such as those of some fungi, where the multicellular organism is haploid, and diploid cells are typically just the zygote, animals have a multicellular diploid stage. Similarly, unlike plants that use meiosis to produce gametes in some stages of their life cycle, animals consistently use meiosis directly to produce haploid gametes.