62 Ecology and Evolution Alternation of Generations Land plants have a two-generation life cycle called alternation of generations: 1. The sporophyte (diploid) generation produces haploid spores by...

Extracted text: 62 Ecology and Evolution Alternation of Generations Land plants have a two-generation life cycle called alternation of generations: 1. The sporophyte (diploid) generation produces haploid spores by meiosis. Spores develop into a haploid generation by mitosis. Label the appropriate arrow "mitosis" in Figure 17.3a. 2. The gametophyte (haploid) generation produces gametes (eggs and sperm) by mitosis. The gametes then unite to form a diploid zygote. The zygote becomes the sporophyte by mitosis. Label the appropriate arrow "mitosis" in Figure 17.3a. In this life cycle, the two generations are dissimilar, and one dominates the other. The dominant generation is larger and exists for a longer period. Figure 17.3 contrasts the plant life cycle (alternation of generations) with the animal life cycle (diploid life cycle). 1. In the plant life cycle, meiosis occurs during the production ofhaploid spores 2. In the human life cycle, meiosis occurs during the production of 3. In the plant life cycle, the generation that produces gametes is (n or 2n) 4. In the human life cycle, the individual that produces gametes is (n or 2n) Figure 17.3 Plant and animal life cycles. a. The alternation of generations life cycle is typical of plants. Mitosis occurs as a spore becomes a gametophyte and as the zygote becomes a sporophyte. Add mitosis to this life cycle in two places. b. The diploid life cycle is typical of animals. Add mitosis to this diagram in one location only. sporophyte (2n) individual (2n) zygote sporangium zygote diploid (2n) FERTILIZATION MEIOSIS haploid (n) diploid (2n) FERTILIZATION MEIOSIS gametes spore haploid (n) gametophyte (n) gametes