Topic 4: Plants (Kingdom Plantae – Ch. 29) – Introduction; Nonvascular Plants
I.
Kingdom
Plantae – general characteristics
A.
eukaryotic,
multicellular, with cell walls rich in cellulose
B.
most are
photosynthetic, with chloroplasts containing chlorophylls a and b
and carotenoids
C.
all have
alternation of generations
D.
dominate nearly
all terrestrial communities (exceptions in tundra); major producers in most of
these habitats
E.
source of food,
shelter, clothing, much of the atmosphere’s oxygen
F.
~300,000
described living species in 10 phyla
G.
two groups:
1.
nonvascular
plants (a grade) and vascular plants (a clade)
2.
vascular plants
divided into those without seeds (a grade) and those with seeds (a clade)
II.
Evolutionary
origin and adaptations to land
A.
related to green
algae
1.
chloroplast
similarity
2.
cellulose in cell
walls
3.
starch as energy
reserve
4.
formation of cell
plate during division (found in plants and some green algae)
5.
genetic
similarities (especially ribosomal RNA sequence); plant clade is ~500 million
years old
6.
distinguished from
green algae because diploid form always begins development within tissues of a
haploid form, and always have heteromorphic
(different-looking) haploid and diploid forms
7.
also
distinguished by adaptations to survival on land, including protecting embryos
B.
revised
classification: Kingdom Viridiplantae
1.
cladistic
analysis shows no clear division between plants (traditional Kingdom Plantae)
and green algae (traditional Phylum Chlorophyta)
2.
instead,
traditional land plants together with some green algae apparently form a
monophyletic group called Streptophyta
3.
the Streptophyta
together with the rest of the green algae apparently form a monophyletic group,
the proposed (and increasingly accepted) Kingdom
Viridiplantae (or Viridaeplantae)
C.
adaptations to
land
1.
plants are
primarily terrestrial – few aquatic species
2.
plants likely
first terrestrial organisms
3.
cell wall helps
prevent water loss (desiccation)
4.
embryos (young
sporophyte plants) protected by some sort of covering to protect against things
like desiccation
5.
most plants have
a waxy cuticle – on exposed
surfaces, relatively impermeable; prevents most water loss
6.
cuticle creates a
problem with gas exchange, so most plants have stomata (singular: stoma)
·
pores that can be
opened and closed for gas exchange
·
up to thousands
per square centimeter on leaves
·
closing helps
prevent water loss
·
must open to let
carbon dioxide in, oxygen out
7.
mycorrhizal
relationships with fungi
·
found in about 90%
of plant species, some absolutely required
·
may help some
with water uptake
·
help tremendously
with nutrient uptake
8.
other adaptations
in some plants
·
vascular tissue
and related structures (roots, shoots, leaves)
·
seeds
·
flowers and
fruits
III. Plant Life Cycles
A.
alternation of
generations – mitosis in both haploid and diploid generations
1.
sporophyte = multicellular diploid organism; makes spores via
meiosis
2.
gametophyte = multicellular haploid organism; makes gametes via
mitosis
3.
plants make
meiospores, but never mitospores
4.
meiosporangia in sporophyte
produces diploid meiospore mother cells (meiosporocytes)
5.
meiosporocyte
undergoes meiosis to produce four haploid meiospores
6.
every “meio-” above is often left off since there are no mitospores;
thus, sporangia, spore mother cells, sporocytes, and spores
7.
meiospores divide
by mitosis, forming gametophyte
8.
gametophyte
produces haploid gametes in special gametangia
structures in some plants
·
antheridium – male gametangia, make sperm
·
archegonium – female gametangia, make eggs
9.
sperm and egg
fuse inside archegonium to form diploid zygote
10.
zygote grows into
sporophyte; young sporophyte = embryo
11.
other activities
occur in some groups, these will be discussed when those groups are covered
12.
evolutionary
trend from “lower” to “higher” plants is a reduction of the gametophyte
generation and an expansion of the sporophyte generation, with more protection
of the embryo
·
nonvascular
plants (mosses, liverworts, hornworts) – gametophyte is green, free-living,
dominant generation
·
seedless vascular
plants (ferns and fern allies) – gametophyte is usually green and free-living,
but sporophyte is dominant generation
·
vascular seed
plants (gymnosperms and angiosperms) – gametophyte is nutritionally dependent
on sporophyte, or may be saprobic
(deriving energy from nonliving organic matter); sporophyte is dominant
generation
IV. Nonvascular Plants
A.
plants lacking
specialized tubes for conducting water and nutrients (that is, lacking vascular
tissue)
B.
gametophytes
photosynthetic and free-living; dominant generation
C.
sporophytes are
attached to and dependent on gametophytes
D.
primitive; likely
the modern plants most similar to the “first plants”
E.
require external
water for sperm to reach eggs for sexual reproduction (swimming sperm)
F.
no true leaves,
stems, or roots (vascular tissue required for true leaves, stems, and roots)
G.
small; rarely
more than 7 cm tall
H.
most common in
and mostly limited to moist places
I.
sometimes called bryophytes
J.
three phyla:
1.
Phylum
Hepatophyta – liverworts
2.
Phylum
Anthocerophyta – hornworts
3.
Phylum Bryophyta
– mosses
V.
Phylum
Hepatophyta – liverworts
A.
some with
flattened bodies (thalli) with lobes resembling liver; “wyrt” is old
English for plant; thus, “liverwort”
B.
thalloid forms
only 20% of phylum; rest look like mosses
C.
simpler than
mosses
1.
gametophytes
develop almost directly from spores (reduced protonema)
2.
gametophyte
growth is prostrate (flat), not erect
3.
rhizoids are
one-celled
D.
sexual
reproduction similar to that in mosses; two small differences:
1.
antheridia on
stalks called antheridiophores
2.
archegonia on
stalks called archegoniophores
E.
asexual
reproduction occurs in thalloid forms from gemmae splashed out of gemma
cups on “leaves”
F.
about 9,000
living species
VI. Phylum Anthocerophyta – hornworts
A.
thalloid
gametophytes (look much like thalloid liverworts)
B.
cells typically
have a single chloroplast, very much like the chloroplast of green algae
C.
sporophyte
partially independent from gametophyte
1.
green;
photosynthetic
2.
functional
stomata
3.
still embedded in
gametophyte, gets some nutrition from it
D.
about 100 living
species
VII. Phylum Bryophyta - mosses
A.
small “leaves”
arranged spirally or alternately around a stem-like axis
B.
“leaves” not true
leaves; only one cell thick, except at midrib
C.
anchored to
substrate with root-like rhizoids (not true roots; no vascular tissue,
little water absorption)
D.
most water
travels up outside of plant by capillary action
E.
sexual
reproduction
1.
male antheridia
and female archegonia on same or separate plants
2.
sperm made in
antheridia swim to archegonia (using flagella to move through dew or rainwater)
3.
sperm unites with
egg in archegonium, forming diploid zygote
4.
zygote undergoes
mitotic divisions and develops into sporophyte
·
slender stalk
with swollen capsule (sporangium) at tip
·
base imbedded in
gametophyte
·
dependent on
gametophyte for nutrients
5.
spore mother
cells in sporangium produce haploid spores
6.
at maturity,
outer covering of sporangium pops off, releasing spores
7.
spores in right
(mainly damp) environment grow into protonemata (singular protonema)
8.
buds from a
protonema become new gametophyte plants
F.
importance/ecology:
1.
about 15,000
living species
2.
can survive some
drought conditions, but not found in deserts
3.
most are very
sensitive to air pollution, good indicators of air quality
4.
important
producers in some habitats such as bogs,
5.
most abundant
plants in
6.
peat mosses (Sphagnum)
found in peat bogs
·
bogs are wetlands
with very acidic, water-logged soils
·
in bogs where Sphagnum
grows abundantly, dead Sphagnum builds up as peat
·
“peat bogs” are
abundant:
§
about 1 billion acres of peat bogs in world
(northern hemisphere mostly)
§
~1% of Earth’s
land surface!
·
harvesting peat is an important industry in northern temperate
zone (
§
peat is used as a
soil conditioner or potting mix for good water-holding capacity (peat absorbs
25x weight in water)
§
peat can also be
used as fuel
§
peat industry is
worth many millions of dollars a year
·
slow
decomposition in peat bogs make them excellent archeological sites
§
bodies and
artifacts buried in bogs are often well-preserved (“Bog people”)
§
allows
archeologists to study vanished societies