Transcript Diversity of Plants - Dublin City University

Diversity of Plants
Features of plants
• Photosynthetic with Chlorophylls a and b
and carotene accessory pigment
• cellulose cell walls
• carbohydrate storage as starch in chloroplast
• Chloroplast structure organised into grana
• mechanisms to protect the zygote
Evolution of plants
• Evolution is driven by the need to absorb,
transport and retain water, and the need to
reduce the requirement of water for
fertilisation.
Groups of plants
• The non-seed, nonvascular plants
Mosses, Liverworts
and Hornworts
• The non-seed vascular
plants
Whisk ferns, Club
mosses, Horsetails,
Ferns
• Gymnosperms
• Angiosperms
Mosses, Liverworts and
Hornworts
• Important today both
ecologically and
economically
• peat-burning provides
part of Ireland's
energy requirements,
and unlike fossil fuels,
peat is a renewable
resource when
properly managed.
• In addition, peatlands
are the habitat of
commercial crops such
as blueberries and
cranberries.
• Important in
horticulture for potting
and as a soil additive
• First colonisers of bare
land
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Mosses, Liverworts and
Hornworts
No leaves
No vascular tissues
No true roots
Poorly defined cuticle
flagellated spores (sperm)
Gametophyte dominant
Sporophyte on gametophyte
Hornworts have a long lived
sporophyte
• Liverworts have a lobed thallus
Life cycle
Spores produced
by meiosis
Fertilisation of egg gives
Diploid sporophyte which
then divides to produce a
stalk and capsule
Archegonium
gives
single egg cell
by mitosis
Sperm
Antheridum
gives sperm by
mitosis
Spore (n)
Female
gametophyte
Male
gametophyte
Protonoma
Development of Moss from the
protonoma
Moss spore
Early protonema
Developing moss plant
Moss reproductive structures
Archegonia
with egg cell
Antheridia give
flagellated sperm
Non-seed, non-vascular plants
and water
• Capillary uptake of
water, sufficient only
for a few centimetres,
restricts the height of
the plant.
• All parts of the plant
must photosynthesise
as no phloem to
transport sugars - no
subterranean roots.
• Abundant water
needed for
germination and
growth of the
protonema
• Need a film of water
for the sperm to swim
in for fertilisation
Seedless vascular plants
• All have phloem and
xylem in the stem to
transport sugars and
water (tracheids only)
• All have underground
stem (rhizome)
• All have essentially
the same reproductive
system with a
dominant sporophyte
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Whisk Ferns
Club mosses
horsetails
ferns
Whisk Ferns (Psilophytes)
• No true leaves, but expanded surfaces
without vascular tissue (enations) - restricts
the length of the enations.
Club mosses (Lycophyta)
• Microphylls (leaves with a
single unbranched vascular
bundle). Leaves may be long
but not wide.
• Now rare, but in past times,
tree-form club mosses more
than 35 metres tall were
abundant
Horsetails
• Microphylls (may be
more than one parallel
vascular bundle)
means leaves may also
be wider.
• Only one genus
Equisetum survives
today although in
carboniferous times,
they were abundant
and tree-sized.
Ferns
• Megaphylls (leaves with branched vascular
bundles). Leaves may be any size or shape.
Life cycle
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Spore bearing leaves (sporophylls) produce
Spore-producing structures (sporangia)
Spores produced by meiosis
Sometimes two different sizes of spores,
microspores and megaspores giving male
and female prothalli, are produced from
microsporangia and megasporangia. This
may explain how seeds originated.
Life cycle of Whisk ferns, Club
mosses, Horsetails and Ferns
Spores produced
by meiosis
Spores germinate
to give protonema N
Sporophylls
Archegonia develop
on the prothallus
Sperm
released
Antheridia develop
on the prothallus
Mature plant is sporophyte 2N
Protonema germinates into a
heart shaped prothallus
Water and non-seed vascular
plants
• Phloem allows
underground, nonphotosynthetic parts
which provide
anchorage and take up
water.
• Xylem allows the
plant to grow to a
great height.
• Plants need water for
growth of the
protonema/ prothallus.
• Need a film of water
for the sperm to swim
in for fertilisation
Gymnosperms
Gymnosperms
• Heterospory - male
and female spores are
different
• Retention and
protection of the
female spores
• Pollination
• Seeds (born naked)
• Well developed roots
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4 subgroups
Conifers
Cycads
Gnetophyta
– Gnetum
– Welwitschia
– Ephedra
• Gingkgophyta
– Ginkgo biloba
Seeds may have evolved by a
megaspore not being shed
Microsporangium
gives microspores
(pollen)
Megaspore not shed
and germinates
on the plant.
Megasporangium 2n
gives a megaspore (n)
Sporophylls
Protonema germinates
into a heart shaped
prothallus
Mature plant is sporophyte 2N
Archegonia develop
on the prothallus
Reproduction in the gymnosperms
nucellus (2n)
= megasporangium
Sporophyll (2n)
Seed bearing scale
leaf (lots of these
make up a cone)
Female gametophyte (n)
= female prothallus
= archegonium (n)
Ovule
= egg (n)
Integuments (2N)
Protective covering
derived from parent
(gives seed coat)
Micropyle (opening to
allow fertilisation)
Angiosperms
• Flowers
• Fruits (seeds not born
naked)
• Endosperm
• Xylem vessels
• Split into two subgroups
• Monocotyledons
• Dicotyledons
Differences between monocots
and dicots
Monocot
Dicot
Venation
Parallel
Reticulate
Cambium
Absent from
bundles
One
Present
Cotyledons
Two
Seed storage Endosperm
Cotyledons
Roots
Tap root
Fibrous
Flower parts 3’s
4’s and 5’s
Monocotyledons
Families within the monocots
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Palms
arums
agaves, amaryllids,
bromeliads
(pineapple)
• yams
• grasses, sedges, cattails
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Irises
lilies
orchids
gingers and bananas
Orders within the Dicotyledons
• Magnoliids (Primitive
flowering plants)
• sunflowers, scrophs,
potato
• Ericads (Blueberries,
etc.)
• "Lower" Hamamelids
(Sycamores, etc.)
• "Higher" Hamamelids
(Oaks, Figs, Elm, etc.)
• Ranunculids
• Rosids (Roses,
Legumes, etc.)
Reproduction
• Essentially the same as • Double fertilisation
gymnosperms except
– normal fertilisation to
give a zygote
that efficient vectored
– fertilisation with 2
pollination.
polar nuclei gives
• Growth of a long
endosperm
pollen tube to deliver
• Developing zygote
the male gametes.
occurs within the
• Fertilisation occurs
enclosing sporophyte
soon after Pollination
tissues - fruits