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Plant Reproduction Notes

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Biological Sciences
BIOSC 0160
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3/4 Chapter 23: Plant Reproduction Alternation of Generations • Plants have distinct haploid and diploid stages during the sexual life cycle • Alternate between n and 2n generations • These stages are physically separate in many plants (ferns) • Sporophyte o Diploid stage o Produced by fertilization o Will undergo meiosis to produce haploid spores (the gametophyte generation; spores ≠ gametes) • Gametophyte o Haploid stage o Produces gametes by mitotic cell division o Spores divide to give rise to male and female (multicellular) gametophytes o Male and female gametophytes join during fertilization to yield a sporophyte • Condition in Angiosperms o Gametophyte develops within sporophyte tissue o Hence, both generations occur in the same plant 3/4 Terminology • Floral Organs o Sepals: outermost whorl; green and leaf-like o Petals: next whorl; brightly colored organs o Stamens: next whorl; where the male gamete develops o Carpels: where the female develops • Complete vs. Incomplete o Complete: plant contains all four floral organs o Incomplete: plant is lacking one of the four organs • Perfect vs. Imperfect o Perfect: plant contains both stamens and carpels o Imperfect: plant lacks either stamens or carpels • Monecy vs. Dioecy o Monecious: both staminate and carpellate o Dioecious: plant has one or the other Gametophyte Development • Males (pollen grains) 3/4 o Microsporocytes are found in sporangia  These will undergo meiosis to produce pollen grains o Four haploid microspores result  Microspores then undergo mitotic cell division • Forms the generative cell, which divides to produce two sperm • Also forms the tube cell, which grows the pollen tube and encloses the generative cell • Female (embryo sac) 3/4 o One megasporocyte in each sporangium  These divide by meiosis to produce four haploid megaspores  Three of the cells die o Survivor divides by mitosis without cytokinesis three times to yield eight nuclei  Cell membranes form  One nucleus is in the egg  Two nuclei are in the large central cell  Two cells become synergids (assist fertilization by directing the pollen tube)  Three cells become antipotal cells (unknown function)  The resulting embryo sac is the female gametophyte o Integuments of sporophyte tissue surround
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