ch 29 plant diversity part 2 -...
TRANSCRIPT
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• Sphagnum, or “peat moss,”
o forms extensive deposits of
par1ally decayed organic
material
§ known as peat
o an important global reservoir of
organic carbon
Moss
(a) Peat being harvested
(b) “Tollund Man,” a bog mummy
Ferns and other seedless vascular plants • Bryophytes and bryophyte-‐like plants
o were the prevalent vegeta1on during the first 100 million years of plant evolu1on
• Vascular plants
o began to diversify during the Devonian and Carboniferous periods
• Vascular 1ssue
o allowed these plants to grow tall
• Seedless vascular plants
o have flagellated sperm and are usually restricted to moist environments
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
Origins and Traits of Vascular Plants • Fossils of the forerunners of vascular
plants
o date back about 420 million years
• These early 1ny plants had independent, branching sporophytes
• Living vascular plants are characterized by:
o Life cycles with dominant sporophytes
o Vascular 1ssues called xylem and phloem
o Well-‐developed roots and leaves
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Life Cycles with Dominant Sporophytes
• In contrast with bryophytes
o sporophytes of seedless
vascular plants are the larger
genera1on
§ as in the fern
• The gametophytes
o 1ny plants that grow on or
below the soil surface
Fig. 29-‐13-‐1
Key
Haploid (n) Diploid (2n)
MEIOSIS Spore dispersal
Sporangium
Sporangium Mature sporophyte (2n)
Sorus
Fiddlehead
Fig. 29-‐13-‐2
Key
Haploid (n) Diploid (2n)
MEIOSIS Spore dispersal
Sporangium
Sporangium Mature sporophyte (2n)
Sorus
Fiddlehead
Spore (n)
Young gametophyte
Mature gametophyte (n) Archegonium
Egg
Antheridium
Sperm
FERTILIZATION
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Fig. 29-‐13-‐3
Key
Haploid (n) Diploid (2n)
MEIOSIS Spore dispersal
Sporangium
Sporangium Mature sporophyte (2n)
Sorus
Fiddlehead
Spore (n)
Young gametophyte
Mature gametophyte (n) Archegonium
Egg
Antheridium
Sperm
FERTILIZATION New sporophyte
Gametophyte
Zygote (2n)
Transport in Xylem and Phloem • Vascular plants have two types of vascular 1ssue:
o xylem and phloem
• Xylem
o conducts most of the water and minerals
§ includes dead cells called tracheids
o strengthened by lignin and provide structural support
• Phloem
o Moves sugars, amino acids, and other organic products
§ consists of living cells
EvoluHon of Roots • Roots
o Organs that anchor vascular plants
o enable vascular plants to absorb water
§ and nutrients from the soil
o May have evolved from subterranean stems
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EvoluHon of Leaves • Leaves
o organs that increase the surface area of vascular plants
§ thereby capturing more solar energy
q used for photosynthesis
• Leaves are categorized by two types:
– Microphylls
– leaves with a single vein
– Megaphylls
– leaves with a highly branched vascular system
• According to one model of evolu1on
o microphylls evolved first
§ as outgrowths of stems
EvoluHon of Leaves
Sporophylls and Spore VariaHons
• Sporophylls
o modified leaves with sporangia
• Sori
o clusters of sporangia on the undersides
of sporophylls
• Strobili
o cone-‐like structures formed from groups
of sporophylls
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• homosporous
o produce one type of spore that develops into a bisexual gametophyte
§ Most seedless vascular plants
• heterosporous
o produce megaspores that give rise to female gametophytes
§ and microspores that give rise to male gametophytes
o All seed plants and some seedless vascular plants
Sporophylls and Spore VariaHons
Homosporous spore production
Sporangium on sporophyll
Single type of spore
Typically a bisexual gametophyte
Eggs
Sperm
Eggs
Sperm
Heterosporous spore production
Megasporangium on megasporophyll Megaspore Female
gametophyte
Male gametophyte
Microspore Microsporangium on microsporophyll
ClassificaHon of Seedless Vascular Plants • There are two phyla of seedless vascular plants:
– Phylum Lycophyta
– includes club mosses, spike mosses, and quillworts
– Phylum Pterophyta
– includes ferns, horsetails, and whisk ferns and their rela1ves
Lycophytes (Phylum Lycophyta)
Selaginella apoda, a spike moss
Isoetes gunnii, a quillwort
Strobili (clusters of sporophylls)
2.5 cm
Diphasiastrum tristachyum, a club moss 1 cm
Fig. 29-‐15e
Pterophytes (Phylum Pterophyta) Athyrium filix-femina, lady fern
Vegetative stem
Strobilus on fertile stem
1.5
cm
25 c
m
2.5
cm
Psilotum nudum, a whisk fern
Equisetum arvense, field horsetail
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Phylum Lycophyta:
• Giant lycophytes
o thrived for millions of years in moist swamps
• Surviving species are small herbaceous plants
• Club mosses and spike mosses have vascular 1ssues
o and are not true mosses
Phylum Pterophyta • Ferns
o most diverse seedless vascular plants
§ more than 12,000 species
• Horsetails
o diverse during the Carboniferous period
§ now restricted to the genus Equisetum
• Whisk ferns
o resemble ancestral vascular plants
§ but are closely related to modern ferns
The Significance of Seedless Vascular Plants • Ancestors of modern lycophytes, horsetails,
and ferns
o grew to great heights during the Devonian and Carboniferous
§ forming the first forests
• Increased photosynthesis
o may have helped produce the global cooling
§ at the end of the Carboniferous period
• The decaying plants of these Carboniferous forests eventually became coal
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You should now be able to:
1. Describe four shared characteris1cs and four dis1nct characteris1cs between
charophytes and land plants
2. Dis1nguish between the phylum Bryophyta and bryophytes
3. Diagram and label the life cycle of a bryophyte
4. Explain why most bryophytes grow close to the ground and are restricted to
periodically moist environments
5. Describe three traits that characterize modern vascular plants and explain how these traits have contributed to success on land
6. Explain how vascular plants differ from bryophytes
7. Dis1nguish between the following pairs of terms: microphyll and megaphyll; homosporous and heterosporous
8. Diagram and label the life cycle of a seedless vascular plant