Biological Science 2/e

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What is a plant? Eukaryote Multicellular Cell
wall of cellulose other polysaccharides Chlorop
hyll photosynthesis
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All plant cells (exept sperm) have a cell wall
made mostly of cellulose.
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Vacuole important in plants With wall, provides
support. Can enlarge quickly, facilitating rapid
growth. Stores nutritional reserves and waste
products.
http//www.agen.ufl.edu/chyn/age2062/lect/lect_06
/5_43.GIF
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Major transitions in plant evolution
360 mya
400 mya
450 mya
700 mya
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Fossil record shows five major intervals.
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Green algae must be bathed in water to live.
Important in aquatic and nearshore ocean habitats.
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Terrestrial plants made the move onto land.
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Benefits of terrestrial life More
sunlight. More carbon dioxide. The first
terrestrial plants resembled the groups below.
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Waxy cuticle reduces water loss. Stomata permit
entry of CO2. (Early land plants had pores but no
guard cells.)
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Vascular plants transport water. and are able to
grow to greater size. Better competitors for
light.

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What key adaptation permitted water
transport? Vascular tissue -- like drinking
straws.
The first vascular plants resembled these groups.
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These primitive vascular plants can be large!
Tree fern Dicksonia antarctica Tasmania
http//www.discover-tasmania.com/ events/big-tree-
hunting.html
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Giant horsetail
Colony of Equisetum giganteum near railroad.
Lluta Valley, Chile. photos by Chad Husby,
December 2002
http//www.fiu.edu/chusb001/ GiantEquisetum/Chil
e.html
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Incredible fossils from Rhynie Chert (400
mya) Show lignin rings around vascular
tissue. Vascular tissue carries water resists
gravity.
http//www.abdn.ac.uk/rhynie/intro.htm Close up
of the stellate xylem strand of Asteroxylon
mackiei showing spiral thickenings (t) (scale bar
100µm).
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Vascular tissues of plants have secondary cell
walls, made of strong, waterproof lignin.
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All vascular plants have tracheids. Water moves
through pits. Must cross primary cell wall.
Like pulling water through a series of straws
with cloth at the end of each straw.
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Vessels are only in more advanced groups. In
vessels, walls are removed at end of mature
cells. Water travels with much less friction.
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Summary Vegetative adaptations to terrestrial
life.
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Reproductive adaptations to terrestrial life. We
consider six. First review simple plant life
cycle.
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Life cycle of green algae. Mostly haploid
diploid zygote only.
Plants bathed in water sperm and spores swim.
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Terrestrial plants have a multicellular diploid
stage as well as a multicellular haploid stage.
Gametophyte makes gametes. Sporophyte makes
spores. b/c both multicellular, called
alternation of generations.
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Adaptation 1 In land plants, multicellular
gametangia prevent gametes from drying out.
Produce sperm eggs Moss reproductive
structures
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In moss, the sperm swims to the egg. The diploid
embryo develops on the female plant.
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/M/MossLifeCycle.gif
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Adaptation 2 In land plants, embryo develops on
maternal plant.
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Adaptation 3 Heterospory. Separate male
and female spores permit development of
specialized male and female gametophytes.
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Adaptation 4 Pollen Specialized male
gametophyte In higher plants than moss and
ferns. Pollen doesnt dry out can be carried by
wind or insect.
http//mse.iastate.edu/images/microscopy/PollenMix
b.jpg
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Adaptation 5 Seed Allows embryo to disperse, or
go dormant.
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Adaptation 6 Flower permits specialized
pollination.
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Pollinator-mediated reproductive isolation can
spur speciation.
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Review of reproductive adaptations of plants.
( and multicellular gametangia)
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Traditional division of flowering plants.
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Dicots are not a monophyletic group.
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Relationships among seed plants not clear.
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Very strange plant grows in NE Africa. May live
to be 1000 years old. Produces only two leaves
(split into strips).
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Cycads look like ferns but have separate male and
female plants produce seeds. Ancient group.
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Female leaves (megasporophylls) with
ovules. These strobili can weigh up to 40 kg.
http//en.wikipedia.org/wiki/Cycad Cycas
revoluta
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Living fossil known only from eastern
China. Planted near temples there.
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Conifers include pines.
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There are about 300,000 species of angiosperms.
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Plant domestication foundation for sedentary life.