BIOL 112 Lecture 22

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No notes from Wednesday due to Exam. No notes from Friday due to bomb threat.

Chapter 30: Evolution of Seed Plants

vascular tissue = taller

seeds, pollen, and flowers: better dispersal of progeny

Gymnosperms

From Greek γυμνοσπερμοσ, meaning "naked seed" First evolved in Carboniferous (~350 mya) and cycads dominated by ~250 mya

The following adaptations are common to all seeded plants, but are tailored for the gymnosperm life cycle

1. further reduction of gametophyte (now microscopic, short-lived structures)
   • c.f. bryophytes, where gametophyte was dominant structure and sporophyte was small, dependent, transient structure
2. heterospory: haploid megaspore becomes female gametophyte (archegonia + egg), haploid microspore becomes male gametophyte (pollen grain)
   • c.f. pterophytes, where a single spore (homospory) becomes a bisexual gametophyte
3. pollen grains: microsporocyte (2n) divides by meiosis to form microspores (n), which divide by mitosis to form pollen grain
   • sperm and tube cell comprise male gametophyte
   • efficient dispersal, and fertilization without water
4. ovule: contains megaspore (formed when megasporocyte (2n) undergoes meiosis)
   • megaspore surrounded by diploid megasporangium and coat (integument)
   • megaspore forms egg and archegonium by mitosis
5. fertilization without water
6. the seed
   • integument becomes seed coat
   • fertilized egg (now a diploid zygote) becomes embryo
   • megasporangium (2n) provides nutrition for embryo at germination

Angiosperms

Similar to gymnosperms, but produce flowers.

Originated from microsporophyll mutation to form stamen/anther?