chapter40Plantreproduction[1]

chapter40Plantreproduction[1] - BLY 122 Chapter 40 Plant...

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Chapter 40 Plant reproduction 1 BLY 122 C. S. Major Chapter 40 Plant reproduction I. An Introduction to Plant Life Cycles A. Sexual Reproduction in Angiosperms 1. Sexual reproduction involves two processes. a. Meiosis—a reduction division that generates haploid gametes. b. Fertilization—fusion of gametes. (1) Male gametes are sperm. (2) Female gametes are eggs. c. Gametes are formed in flowers. ( Fig. 40.1 ) 2. Location of male and female reproductive organs is variable. a. Flowers with both male and female organs are perfect. b. Flowers with either male or female organs are imperfect. c. In monoecious plants, separate male and female flowers are located on the same plant. ( Fig. 40.2a ) d. In dioecious plants, male and female flowers are located on different plants. ( Fig. 40.2b ) B. Plant Life Cycles—an Alternation of Generations 1. Two multicellular generations comprise the plant life cycle. a. The generation composed of diploid cells is the sporophyte. (1) Cells in the sporophyte generation undergo meiosis and produce haploid spores; this occurs in sporangia. (2) Spores divide by mitosis to form the multicellular gametophyte generation; this occurs in gametangia. b. The generation composed of haploid cells is the gametophyte. (1) Cells in the gametophyte generation produce gametes by mitosis. (2) One gamete must fuse with another gamete to form a diploid zygote that develops into the sporophyte generation. 2. Relationship between the generations varies between plant groups. a. In mosses and liverworts the sporophyte generation is small, short-lived, and dependent on the gametophyte for nutrients. ( Fig. 40.3a ) b. In flowering plants the gametophyte generation is small, short-lived, and dependent on the sporophyte for nutrients. ( Fig. 40.3b ) C. Asexual Reproduction 1. Asexual reproduction leads to new individuals without meiosis and fertilization. 2. Offspring produced are clones—genetically identical to the parent plant. a. Same pairs of alleles are found in same combinations as in parents. b. No new alleles are introduced from other individuals. 3. Asexual reproduction is efficient and rapid. a. Asexually produced offspring can grow quickly and fill niches before competitors arrive. b. Parent plant can provide nutrients for early development. 4. Plants reproduce asexually in various ways. a. Rhizomes are horizontal underground stems with nodes that produce shoots and roots. ( Fig. 40.4a ) b. Corms are belowground stems that form new individuals. ( Fig. 40.4b ) c. Plantlets are formed from meristematic tissue on leaf margins of some plants ( Fig. 40.4c ) 5. Genetic similarity of asexually produced individuals makes them more vulnerable to disease-causing agents.
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