Transcript Bio 1082L Intro to Plants

Plants
Land plants retain derived features they share
with green algae:
– Chlorophyll a and b.
– Starch as a storage product.
– Cellulose in cell walls.
2 Major Divisions
• Vascular plants, or tracheophytes
(seven
clades)—all have conducting cells called
tracheids; vessels for transport of H2O,
nutrients, minerals, etc. [xylem & phloem]
• Nonvascular plants: the remaining three
clades—liverworts, hornworts, and mosses;
no vessels.
All land plants have a life cycle with alternation
of generations.
Includes multicellular diploid (2n)(sporophyte)
and multicellular haploid (1n) (gametophyte)
individuals.
p. 614
Nonvascular Plants
• The plant you ‘see’ is the gametophyte (1n);
they are photosynthetic and nutritionally
independent from the next generation.
• The sporophyte (2n) is dependent & attached
to the gametophyte-cannot live without it
(may or may not be photosynthetic)
Nonvascular Plants
Female: archegonium; produces one egg.
Male: antheridium; produces many sperm with
two flagella each.
Water splashes sperm from antheridium to
archegonia where they unite with egg to form
an embryo (2n).
Embryo develops into sporophyte (2n).
p. 615
Liverworts
Some have leafy gametophytes; some have thalloid
gametophytes.
Sporophytes very short—a few mm.
A stalk raises the simple sporangium above ground
level to allow spores to be dispersed.
Liverworts also reproduce asexually:
by simple fragmentation of the gametophyte;
by gemmae—lens-shaped clumps of cells in
gemmae cups. Gemmae are dispersed by
raindrops.
p. 623
Liverworts
Liverworts
Gemmae
Hornworts
Gametophytes are flat plates of cells.
Have stomata, which do not close.
Hornwort cells have a single, large chloroplast.
The sporophyte has no stalk; but has a basal
region capable of infinite cell division.
Sporophytes can grow up to 20 cm.
Hornworts have internal cavities filled with
nitrogen-fixing cyanobacteria.
Hornworts
p. 623
Mosses (Bryophytes)
Gametophyte begins as a branched, filamentous
structure—the protonema.
Some filaments are photosynthetic, others are
rhizoids that anchor the protonema.
Tips of photosynthetic filaments form buds which
produce the leafy moss shoots.
Moss sporophytes and vascular plants grow by
apical cell division—a region at the growing tip
provides an organized pattern of division,
elongation, and differentiation.
Mosses
Some moss gametophytes are too large to
depend on diffusion for water transport.
Cells called hydroids die, and provide channels in
which water can travel.
Hydroids may be the progenitor of tracheids.
Mosses
Vascular Plants
Developed Heterospory: produce two types of
spores:
Megaspore develops into female
gametophyte—megagametophyte:
produces small numbers of spores.
Microspore develops into male
gametophyte—microgametophyte:
produces large numbers of spores.
Does not rely on H2O for fertilization!!
p. 622
Horsetails & Whisk Ferns
Horsetails: Silica in cell walls—“scouring rushes.”
Have true roots; sporangia are on short stalks
called sporangiophores.
Leaves are reduced megaphylls in whorls. Each
stem segment grows from the base.
Whisk ferns: No roots but well-developed
vascular system.
Psilotum flaccidum has scales instead of leaves.
Tmesipteris has flattened, reduced megaphylls.
Ferns
Ferns: Sporophytes have true roots, stems, and
leaves. Starts development as a coiled
“fiddlehead.” (p. 626)
Fern Life Cycle
Spore mother cells in sporangia form haploid
spores by meiosis.
Spores can be blown by wind and develop into
gametophyte far from parent plant.
Fern gametophytes produce antheridia and
archegonia, not always at the same time or on
the same gametophyte.
Sperm swim through water to archegonium to
fertilize egg.
Zygote develops into independent sporophyte.
p. 627