Final answer:
The gymnosperm life cycle includes both haploid and diploid phases. Haploid gametophytes produce gametes, while the diploid sporophyte grows from the zygote into the mature plant. This exemplifies the alternation of generations, a typical plant reproduction process.
Step-by-step explanation:
In the life cycle of gymnosperms, such as sequoias and pines, there are two distinct phases: haploid and diploid phases. The haploid phase is represented by the gametophytes, which develop from haploid spores after meiosis. These gametophytes are responsible for producing gametes through mitosis. On the other hand, the diploid phase, known as the sporophyte, is the dominant phase and develops from the zygote after the fusion of gametes. This sporophyte is what we commonly recognize as the plant itself, such as the towering trees mentioned.
In gymnosperms, the gametophytes are microscopic structures, with male gametophytes found in pollen grains and female gametophytes within the ovule. Once fertilization occurs, the zygote will grow into a mature sporophyte, completing the cycle. This process is an example of the alternation of generations, which is typical for plant reproduction, indicating the change between haploid (gametophyte) and diploid (sporophyte) stages.