Lab 5
Exercise 5: Gymnosperms and Angiosperms
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OBJECTIVES:
1. Describe the distinguishing features of gymnosperms and angiosperms.
2. Understand the evolutionary significance of pollen and seeds.
3. Understand the function of a cone, a flower, and a seed.
4. Relate the life cycle of angiosperms to the other phyla of the plant kingdom.
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INTRODUCTION TO GYMNOSPERMS
Gymnosperms are plants with exposed seeds borne on scale-like structures called cones (strobili). Like ferns, gymnosperms have a well-developed alternation of generations, but unlike most ferns, gymnosperms are heterosporous - they produce two types of spores (Fig. 1). Microspores occur in male cones and form male gametophytes. Megaspores occur in female cones and form female gametophytes. Gametophytes of gymnosperms are microscopic and completely dependent on the large, free living sporophyte. One advantage of this is that the delicate female gametophytes do not have to cope with environmental stressors - female gametophytes and the embryos they produce are sheltered from drought and harmful UV radiation by their enclosure within the moist reproductive tissues of the parental sporophyte generation. Nutrient exchange also occurs between gametophytes and their parents. In contrast, the free-living gametophytes of seedless vascular plants must fend for themselves. In gymnosperms, pollination is the transfer of pollen (Fig. 2) from male cones (where pollen is produced) to female cones, which house eggs. In these plants, pollen is carried from male cones to female cones by wind - gymnosperms were the first plants to evolve that did not need free water to transfer sperm to egg, and were therefore able to thrive in terrestrial habitats. Pollen grains are also protected by tough coats. After fertilization, seeds are produced with developing embryos
______________________________________________________________________________
OBJECTIVES:
1. Describe the distinguishing features of gymnosperms and angiosperms.
2. Understand the evolutionary significance of pollen and seeds.
3. Understand the function of a cone, a flower, and a seed.
4. Relate the life cycle of angiosperms to the other phyla of the plant kingdom.
______________________________________________________________________________
INTRODUCTION TO GYMNOSPERMS
Gymnosperms are plants with exposed seeds borne on scale-like structures called cones (strobili). Like ferns, gymnosperms have a well-developed alternation of generations, but unlike most ferns, gymnosperms are heterosporous - they produce two types of spores (Fig. 1). Microspores occur in male cones and form male gametophytes. Megaspores occur in female cones and form female gametophytes. Gametophytes of gymnosperms are microscopic and completely dependent on the large, free living sporophyte. One advantage of this is that the delicate female gametophytes do not have to cope with environmental stressors - female gametophytes and the embryos they produce are sheltered from drought and harmful UV radiation by their enclosure within the moist reproductive tissues of the parental sporophyte generation. Nutrient exchange also occurs between gametophytes and their parents. In contrast, the free-living gametophytes of seedless vascular plants must fend for themselves. In gymnosperms, pollination is the transfer of pollen (Fig. 2) from male cones (where pollen is produced) to female cones, which house eggs. In these plants, pollen is carried from male cones to female cones by wind - gymnosperms were the first plants to evolve that did not need free water to transfer sperm to egg, and were therefore able to thrive in terrestrial habitats. Pollen grains are also protected by tough coats. After fertilization, seeds are produced with developing embryos