View
130
Download
0
Category
Tags:
Preview:
DESCRIPTION
Mosses and Ferns. Evolutionary developments necessary for plants to colonize land. Stage One: Becoming multicellular. Occurred in water. Enables specialized tissues to develop. Stage Two: Developing sporangia. Enables dispersal on land. Stage Three: Developing a large sporophyte. - PowerPoint PPT Presentation
Citation preview
Mosses and Ferns
Stage One: Becoming multicellular
Stage Two: Developing sporangia
Occurred in waterEnables specialized tissues to develop
Enables dispersal on land
Stage Three: Developing a large sporophyteConfers competitive advantageProvides perennial spore production
Stage Four: Removing dependence of fertilization on a film of water
Enables survival in dry environments
Evolutionary developments necessary for plants to colonize land
History of evolution of major plant types on land
Stage One of adaptation to living on land The land that plants colonized was hostile to life.
Land plants required several adaptations to be successful that require multi-cellular tissues :
mechanical strength for support,exposed light catching surfaces,anchoring system,conducting system for water,system for obtaining mineral nutrients,a way to restrict water loss in desiccating air,a means of reproducing and dispersing on land
Soil development was minimal.
Devonian
plant community
Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370-380 million years ago.
Simple dichotomous branching
MAIN FEATURES
!5 to 30 cm tall
No roots
Stomata with guard cells
Most had a central vascular strand
Cuticle
Asteroxylon had leaves –without a vascular connection
Sporangia
Asteroxylon
To live on land plants faced two challenges for their reproduction:
1. Dispersal
2. Fertilization
Dispersal was solved first – through production of sporangia.
angeion is Latin for caseSo a sporangia is a spore case
The important feature of sporangia is that they lift spores above the ground so they can be dispersed by the wind
Plants living in water release spores and gametes that swim and may be helped to dispersed by water movement
Stage Two: Developing sporangia
1. Dispersal
Meiosis in the sporangium producing haploid spores.
Mosses
Retention of the zygote by the female gametophyte
Archegonium
Zygote
Delayed meiosis and growth of the sporophyte by mitosis
Gametophyte
Developingsporophyte
Sporophyte – diploid plant that grows from the zygote and produces spores by meiosis
Gametophyte – haploid plant that develops from a spore and produces gametes by mitosis
Gametangium – a “case” holding gametes
Sporangium – the “case” holding spores
Gametes – collective term for sperm and egg
Spores – haploid, single cells produced by meiosis
Eight Terms to Learn to understand Alternation of Generations of Land Plants
Antheridium – The male gametangium
Archegonium – flask–shaped container holding the egg cell. (Ancient gonad) The female gametangium.
The word “phyte” is Greek for plant
Moss life cycleFig. 25.4, p. 406
Zygote grows, develops into a sporophyte while still attached to gametophyte.
Fertiliztion
zygote
Sperm reach eggs by moving through rain drops or film of water on the plant surface.
sperm-producing structure at shoot tip of male gametophyte.
egg-producing structure at shoot tip of female gametophyte.
Diploid StageHaploid Stage
Mature sporophyte (spore-producing structure and stalk), still dependent on gametophyte.
Meiosis
Spores form by way of meiosis and are released.
Spores germinate. Some grow and develop into male gametophytes.
Other germinating spores grow and develop into female gametophytes.
rhizoid
Moss sporophyte
Top of capsule
Developing protonema
Moss antheridium and archegonium
HAPLOID
DIPLOID
Sporesn
Meiosis
Mitosis
Gametes (?)
Fusion (syngamy)
Mitosis
Zygote2n
Female gamete remains attached to the haploid thallus
Development of gametophyte thallus
Development of sporophyte thallus – remains attached to gametophyte
Important life cycle features of mosses
Hydrated
Dry
RAPID WATER LOSSRAPID WATER LOSSConstitutive CellularConstitutive Cellular
ProtectionProtection
Rehydrated
Induction of Induction of Recovery and Recovery and RepairRepairMechanismsMechanisms
Hormone ?Hormone ?
Dessication tolerance in Tortula ruralis
Fig. 25.5, p. 407
The species forms clumps- minimizing surface area to volume ratio.
Unique leaf cells (hyaline cells) of Spahgnum species enable the plant to absorb up to 20 times its own dry weight of water.
Spagnum – the bog-forming species
1. Plants accumulate matter and make growth
2. Plant growth is an organized process following rules of anatomy and morphology
3. Plants maintain their heat and water balance
4. Plants have a life cycle with reproduction and dispersal
5. Evolution is a constant process
How can we characterize mosses?
Stage Three: Developing a large sporophyte
In ferns the sporophyte is only dependent on the gametophyte for obtaining nutrient, water, and physical support when it is first formed.
Large size enables competition as well as effective spore dispersal. The perennial root stock enables continued frond and spore production from year to yearSporophyte
originally grows from a gametophyte and then develops roots, rhizome, and fronds
Ferns
Fronds growing from a rhizome
Fern life cycleThe sporophyte (still attached to the gametophyte) grows, develops.
zygote
fertilizationDiploid Stage
Haploid Stage
egg
sperm
egg-producing structure
sperm-producing structure
mature gametophyte (underside)
Spores develop.
meiosis
sorus (one of the spore-producing structures)
Spores are released
Spore germinates, grows into a
gametophyte.
Archegonia
Antheridia
Sporangia Polypodium spp
sori
sporangia
http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html
A sorus
Magnified sporangia
Polypodium spp
Sporangia
Developing spores
Gametophyte
Polypodium spp
Gametophyte
Developing sporophyte
Arrangement of sporangia on two ferns
In lines on a broadleaved type At the end of the leavesAdiantumAsplenium
Cibotium menziesii in habitat in Hawaii. Photo courtesy of Peter Richardson.
Cyathea australis with the uncurling croziers visible. Photo courtesy of Scott Ridges
Tree ferns
Conducting tissue
1. Plants accumulate matter and make growth
2. Plant growth is an organized process following rules of anatomy and morphology
3. Plants maintain their heat and water balance
4. Plants have a life cycle with reproduction and dispersal
5. Evolution is a constant process
How can we characterize ferns?
Jungle-like forests of the Carboniferous were dominated by giant ancestors of club mosses, horsetails, ferns, conifers, and cycads.
Most of the plant fossils found in the coals and associated sedimentary rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variation in the climate (tropical).
Coal formation
Anaerobic conditions and periodic inundations of the sea
Early Carboniferous
Britain
Ice cap
EquatorAppalachians
Britain
Ice cap
EquatorAppalachians
Recommended