BIOL 112 Lecture 20

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Exam 2 Next Wednesday over Ch. 25-29

See eLearning for learning objectives and homework questions & answers.

Derived Characteristics of Plants

How plants are different from charophyceans

1. Meristems (cell proliferation at growing tips)
2. Alternating Generations
3. Sporangia (house spores)
4. Gametangia (Chamber for gametes in gametophyte)
   • archegonia contain eggs (partially dependent on parent gametophyte)
   • antheridia contain sperm (he he.. plant scrotum)

Alternation of Generations

1. Multicellular diploid sporophyte (2n)
2. haploid spores created by meiosis (n)
3. spores undergo mitosis to form multicellular haploid gametophyte (n)
4. gametophyte undergoes mitosis to form gametes (egg, sperm) (n)
5. Fertilization produces zygote (2n)
6. zygote undergoes mitosis to form multicellular diploid sporophyte (2n)

Evolutionary trend of gametophytes: get smaller and less water-dependent

• Nonvascular seedless: large gametophyte, small sporophyte
• Vascular seedless: mid-sized gametophyte and sporophyte
• Vascular seed: huge sporophyte, microscopic gametophyte

Plant Phylogeny

• Ancestral Plants → bryophytes & [vascular]: 475 mya (evidence from spore fossils)
• [Vascular] → pferophytes (ferns) & [seeded plants]: 420 mya
• [Seeded Plants] → gymnosperms & angiosperms: 360 mya

2 major adaptations:

• vascular tissue: enabled plants to grow taller and have thicker tissues
• seeds and flowers: increased fertilization, dispersal, and survival of progeny

Bryophytes

• Nonvascular, seedless
• e.g. liverwort, hornwort, moss
• Form mats on forest floor
• require lots of moisture (esp. for reproduction in transporting sperm to egg)
• Main form is gametophyte