lecture 6: seed-free to freed seeds Flashcards
lycophytes
1st type of seedless vascular plant including club mosses, spikemosses, and quillworts
◆ leaves and roots evolved independently (relative to the rest of the vascular plants)
◆ leaves and microphyyls w a single, unbranche vein, branching only occurs at shoot tip
◆ carboniferous period
- got hella tall
monilophytes
2nd type of seedless vascular plant including ferns, horsetails, and whisk ferns
◆ leaves are megaphylls with branched veins
◆ potential for stem branching not limited to shoot tip
microphyll / megaphyll / sporophyll
microphyll:
- type of plant leaf with one single, unbranched leaf vein
- few plants exist today
- no leaf gap
◆ clubmosses, horsetails
megaphyll:
- multiple veins within the leaf
- leaf gaps above them
the Carboniferous Period
◆ plants get tall (lycophyte trees, large plants)
◆ plants expand two CO2 sinks
- increases release of calcium and magnesium, which form carbonate and are deposite in marine rocks
- boggy soils were highly water logged, leading to peat and coal
◆ lower CO2 level = big drop in global temp
- leads to polar ice caps
◆ after this period, seed plants come to dominate the landscape
Azolla / the Azolla Event
◆ a time period after Paleocene-Eocene Thermal Maximum consisting of a drop in temperature
◆ azolla (aka fairy moss, mosquito fern, water fern)
- history: dead azolla mats accumulated as stagnant sediment over freshwater, drawing 80% of CO2 out of atmosphere
- aquatic and very reduced in form compared to other ferns
- forms a symbiotic association with nitrogen-fixing cyanobacteria that it makes a home for within pouches in its leaves
- doubles its biomass very fast
- part of a system for organic rice farming
heterospory
◆ characteristic of gymnosperms (seed plants)
◆ make two types of spores, each from a different type of sporangium
(a) Megasporangia – make megaspores that germinate to become the female gametophyte
(b) Microsporangia – make microspores that germinate to become the male gametophyte (pollen)
- each sporangium type is produced by a different type of cone (either on same or different tree)
gymnosperms
◆ vascular, seed plant
◆ gymnos = “naked”, perms = “seed”
◆ produce seeds and pollen in cones
- pollen = solution to adapting to life on land relating to fertilization
- utilizing wind pollination
◆ includes: gnetophytes, cycads, gingko, conifers (coast redwood, giant sequoia, bristlecone pine)
◆ are heterosporus
seeds
evolved to protect and sustain the early sporophyte (better than sporopollenin protects spores)
◆ 3 components of the seed:
(1) embryo – zygote + mitosis (offspring sporophyte)
(2) food supply – remaining female gametophyte tissue in spore wall (from maternal gametophyte)
(3) seed coat – hardened integument (from maternal sporophyte)
◆ able to withstand desiccating conditions that free-living gametophytes cannot
ovulate cone
◆ ovule = megasporangium surrounded by the protective structure that will become the seed coat (NOT dispersed)
ROLE: protect the femal gametophyte
◆ overview:
- the sporophyte (2n) makes ovulate cones
- ovulate cones are made up of sporophylls (2n) that hold megasporangia (2n)
- megasporangia (2n) make megaspores (n) by meiosis
- megaspores (n) germinate to develop into female gametophytes (n)
◆ ovulate cones are pollinated when they are quite small
pine tree life cycle
◆ cone: gymnosperm reproductive structure
- scales of cones are modified leaves with sporangia
◆ in a pollen cone…
- microspores are not dispersed
- free-living male gametophyte moves by wind, not water
- pollen is encased in sporopollenin –> has undergone 2 cell division
- no more motile sperm and no antheridia
◆ ovulate cone
◆ overview
- the sporophyte (2n) makes pollen cones
- pollen cones are made up of sporophylls (scales, 2n)
- sporophylls/scales hold microsporangia (2n) and make microspores (n) by meiosis
- microspores germinate to develop into pollen grains (n)
scale
(of cones) modified leaves with sporangia
(i.e., they are sporophylls and part of the 2n sporophytes)
megaspore / megasporangium
one of two types of spores that gymnosperms make
◆ megasporangia = make megaspores that germinate to become the female gametophyte
microspore / microsporangium
one of the two types of spores that gymnosperms make
◆ microsporangia = make microspores that germinate to become the male gametophyte (pollen)
pollen tube
sperm is shuttled down pollen tubes vs. being motile sperm
pollination
the transfer of pollen to the part of a seed plant containing the ovules
- pollen cones produce heaps of pollen
