Chapter 29: Plant
Diversity I:
How Plants Colonized
Land
By: Jenny Quach
29.1 - Land Plants Evolved from Green
Algae
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Different products than from primary metabolic
pathways
Bitter taste, strong odour, toxic effects; defense
against herbivores/parasites,
Absorb UV radiation
Derived Traits of Plants:
5 Key traits in land plants absent in charophyceans set first plants
apart from algal relatives
1. Apical meristems
2. Alternation of generations
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Sporophytes (2n) produce spores (n) that develop into
gametophytes (n). Gametophytes produce gametes
that unite into zygotes (2n) which develop into
sporophytes (2n)
Charophyceans (Green algae) are the closest relative
of land plants
Morphological/Biomechanical Evidence:
Many key similarities between plants and protists (algae):
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Multicellular, eukaryotic, photosynthetic autotrophs
Cell wall made of cellulose
Chloroplasts with chlorophylls a & b
4 Key Traits of Land Plants & Charophyceans Suggest Close
Relationship:
1. Rosette cellulose-synthesizing complexes
2. Peroxisome enzymes
3. Structure of flagellated sperm
4. Formation of a Phragmoplast
Adaptations Enabling the Move to Land:
Natural selection favours individuals that can survive periods
when not submerged in water
Charophyceans have a durable polymer layer called sporopollenin
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Prevents exposed zygotes from drying out
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Lead to first land plants being able to live permanently
about the waterline
29.2 Land Plants Possess a Set of Derived
Terrestrial Adaptations
Land plants have a far greater risk of drying out
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Possess cuticle made of polyesters and waxes
Waterproof, prevents water loss, protects from
microbial attacks
Many land plants produce molecules called "secondary
compounds"
3. Walled spores produced in sporangia
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Generate haploid spores
4. Multicellular gametangia
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Female gametangia called archegonia; produces eggs
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Male gametangia called antheridia; produces sperm
5. Multicellular dependent embryos
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Similar to humans and other placental animals
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"Embryophytes" another name for land plants
Land plants can be grouped based on presence/absence of
extensive system of vascular tissue:
Non-vascular plants
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"Bryophytes"
Vasular plants:
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Seedless (Lycophytes, Pterophytes)
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Seeded (Gymnosperms, Angiosperms)
29.3 Life Cycles of Mosses and Other
Bryophytes (Non-vascular plants) are
dominated by the Gametophyte stage
Bryophyte Gametophytes:
Gametophytes anchored by delicate rhizoids
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Do not play a role in water/mineral absorption
Bryophyte Sporophytes:
Remain attached to parental
gametophytes
Foot - Embedded in archegonium absorbs nutrients from
gametophyte
Seta (stalk) - Conducts nutrients to
sporangium
Sporangium (Capsule) - produces
spores by meiosis
Calyptra - protective cap on
immature capsule
Peristome: Upper part of capsule
for gradual spore discharge
Hornwort/moss sporophytes have
specialized pores called stomata:
Main Traits that Characterize Living Vascular Plants:
1. Life Cycles with dominant Sporophytes
Opposite to Bryophytes
2. Transport in Xylem and Phloem
Xylem: Conducts most water and minerals
Includes tracheids: tube shaped cells
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Strengthened by lignin
Phloem: Living sugar conducting cells
Lignified (strengthened) vascular tissue permitted plants to grow
to greater heights
Evolution of Roots:
Organs that anchor vascular plants and enable them to absorb
water and nutrients from the soil
Evolution of Leaves:
Organs that increase surface area of vascular plants, thereby
capturing more solar energy for photosynthesis
Microphylls:
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Small, spine-shaped leaves with single vein
Megaphylls:
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Also present in vascular plants
Support photosynthesis by allowing exchange of
CO2/O2 between exterior and interior of sporophyte
Can close to minimize water loss
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Leaves with highly branched vascular system
Much larger
Greater surface area and greater photosynthetic
productivity
Peat moss (Sphagnum):
Sporopylls and Spore Variations:
Forms deposits of partially decayed organic material known as
peat
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Decay is inhibited in peat bogs due to:
- Low temperatures, low nutrient levels,
secondary compounds secreted from peat moss
Peat bogs preserve mummified corpses for thousands
of years
400 billion tons of organic carbon stored as peat
Peat is harvested and used as a fuel source around the world
including Canada
29.4 Ferns and Other Seedless Vascular
Plants Formed in the First Forests
More complex bodies with multiple sporangia increased
survival/reproductive rate
Sporophylls: Modified leaves that bear sporangia
Sori: Clusters of sporangia (Fern Sporophylls)
Strobili: Cones formed by groups of sporophylls
Homosporous: One type of sporophyll producing one type of
spore that develops into bisexual gametophyte
Heterosporous: Two types of sporophyll, two types of spores that
develop into male and female gametophytes