overview of green plants
DESCRIPTION
Overview of Green Plants. Chapter 30. Defining Plants. The kingdom Viridiplantae includes land plants and green algae Red and brown algae are excluded The green algae split into two major clades Chlorophytes Charophytes Streptophyta includes the Charophytes and all land plants - PowerPoint PPT PresentationTRANSCRIPT
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Overview of Green PlantsChapter 30
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Defining Plants• The kingdom Viridiplantae includes land
plants and green algae– Red and brown algae are excluded
• The green algae split into two major clades– Chlorophytes– Charophytes
• Streptophyta includes the Charophytes and all land plants
• All green plants arose from a single species of freshwater algae
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Defining Plants
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Defining Plants
• Land plants have two major features
1. Protected embryos2. Multicellular haploid and diploid phases
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Defining Plants
Adaptations to terrestrial life • Evolution of leaves that increase
photosynthetic surface area• Protection from desiccation by a waxy cuticle
and stomata• Shift to a dominant vertical diploid generation
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Plant Life Cycles
• Humans have a diplontic life cycle– Only the diploid stage is multicellular
Plants have a haplodiplontic life cycle– Multicellular diploid stage = Sporophyte– Multicellular haploid stage = Gametophyte
• Plants have an alternation of generation– sporophyte → gametophyte → sporophyte → etc.
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Plant Life Cycles
• Sporophyte (2N) produces haploid spores (N) by meiosis
• Spores (N) divide by mitosis producing the gametophyte (N)
• Gametophyte (N) produces gametes (N) by mitosis
• Gametes (N) fuse to form the diploid sporophyte (2N)
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The General Plant Life Cycle
process
process
process
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Plant Life Cycles
As more complex plants evolved:
• Diploid stage (sporophyte) became the dominant portion of the life cycle
• Gametophyte became more limited in size• Sporophyte became nutritionally
independent
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Chlorophytes• Chlorophytes, sister taxa of the Streptophytes,
are a diverse group including:
• Chlamydomonas– Unicellular chlorophyte
with two flagella– Have eyespots to direct
swimming– Reproduces asexually as
well as sexually
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Chlorophytes
• Volvox – Colonial chlorophyte
– Hollow sphere of a single layer of 500-60,000 cells
– A few cells are specialized for reproduction
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Chlorophytes
• Ulva – Multicellular chlorophyte– True haplodiplontic life
cycle– Gametophyte and
sporophyte have identical appearance
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MITOSIS
Ulva life cycle
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Land plants
Charophytes
• Charophytes are green algae related to land plants
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Charophytes
• Charales (300 species) – Macroscopic– Plant-like plasmodesmata– Sister clade to land plants
• Choleocaetales (30 species) – Microscopic– Plant-like mitosis– Next closest plant relatives
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Bryophytes
• Bryophytes are the closest living descendants of the first land plants– Called nontracheophytes because they lack
tracheids (specialized transport cells)– Simple, but highly adapted to diverse terrestrial
environments– Non-photosynthetic sporophyte is nutritionally
dependent on the gametophyte– 3 groups: liverworts, hornworts and mosses
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Bryophytes
• Liverworts (phylum Hepaticophyta)– Have flattened gametophytes with liver-like
lobes– Form gametangia
in umbrella-shaped structures
– Also undergo asexual reproduction
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Bryophytes
• Hornworts (phylum Anthocerotophyta)– Sporophyte has stomata
– Sporophyte is photosynthetic
– Cells have a single large chloroplast
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Bryophytes
• Mosses (phylum Bryophyta)– Gametophytes consist of small, leaflike
structures around a stemlike axis– Anchored to substrate by rhizoids– Multicellular gametangia form at the tips of
gametophytes• Archegonia – Female gametangia• Antheridia – Male gametangia
– Mosses withstand drought, but not air pollution
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Moss Reproduction
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Tracheophyte Plants
• Cooksonia, the first vascular land plant, appeared about 420 MYA
– Only a few centimeters tall
– No roots or leaves– Homosporous
(spores are the same size and type)
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Tracheophyte Plants• Vascular tissues are of two types
– Xylem – Conducts water and dissolved minerals upward from the roots
• contains tracheids– Phloem – Conducts sucrose and hormones
throughout the plant• These enable enhanced height and size in
the tracheophytes• Tracheophytes are also characterized by
the presence of a cuticle and stomata
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Tracheophyte Plants
• Vascular plants have gametophytes reduced in size and complexity relative to sporophytes
• Seeds– Highly-resistant structures that protect the plant
embryo– Occur only in heterosporous plants
• Fruits in flowering plants add a layer of protection to seeds – Also attract animals that disperse seeds
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Tracheophytes
• Vascular plants (tracheophytes) include seven extant phyla grouped in three clades
– Lycophytes (club mosses) – Pterophytes (ferns and their relatives) – Seed plants
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Lycophytes
• Club mosses are the earliest vascular plants– They lack seeds
– Superficially resemble true mosses but they are not related
– Homosporous or heterosporous
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Pterophytes• The phylogenetic relationships among ferns
and their relatives is still being sorted out
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Pterophytes• Whisk ferns
– Saprophyte consists of evenly forking green stems without leaves or roots
– Some gametophytes develop elements of vascular tissue
– Often symbionts with fungi
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Pterophytes• Horsetails
– All 15 living species are homosporous– Constitute a single genus, Equisetum
– Consist of ribbed, jointed photosynthetic stems that arise from branching rhizomes
– High silica content in stems made them useful as “scouring rushes”
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Pterophytes
• Ferns– The most abundant group of seedless vascular
plants with about 11,000 species
– The conspicuous sporophyte and much smaller gametophyte are both photosynthetic
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Pterophytes
• The fern life cycle differs from that of a moss– Much greater development, independence and
dominance of the fern’s sporophyte
• Fern morphology– Sporophytes have rhizomes– Fronds (leaves) develop at the tip of the
rhizome as tightly rolled-up coils then uncoil and expand
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Pterophytes
Uncoiled fronds are called “fiddleheads” and are a delicacy among northern First Nation peoples
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Pterophytes
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Pterophytes
• Fern reproduction– Most fern are homosporous– Produce distinctive sporangia in clusters called
sori on the back of the fronds– Diploid spore mother cells in sporangia produce
haploid spores by meiosis– At maturity, the spores are catapulted by
snapping action
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Seed Plants
• Seed plants first appeared 305-465 MYA– Evolved from spore-bearing plants known as
progymnosperms• The seed represents an important advance
– Protects the embryo– Easily dispersed– Introduces a dormant phase in the life cycle
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Seed Plants
• Seed plants produce 2 kinds of gametophytes– Male gametophytes
• Pollen grains• Dispersed by wind or a pollinator
– Female gametophytes • Develop within an ovule• Enclosed within diploid sporophyte tissue
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• There are two types of seed plants– Gymnosperms are plants with “naked seeds”
• Ovule is exposed on a scale at pollination• All lack flowers and fruits of angiosperms
– Angiosperms are flowering plants• Ovules are enclosed in diploid tissue at pollination• The carpel (modified leaf) covers seeds and
develops into fruit
Seed Plants
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• There are four living groups– Cycadophytes– Gnetophytes– Ginkgophytes– Coniferophytes
Gymnosperms
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Gymnosperms
• Cycads (phylum Cycadophyta)– Slow-growing gymnosperms of tropical and
subtropical regions
– Sporophytes resemble palm trees
– Have largest sperm cells of all organisms!
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Gymnosperms
• Gnetophytes (phylum Gnetophyta)– Only gymnosperms with vessels in their xylem
– Contain three (unusual) genera
• Welwitschia• Gnetum• Ephedra
– ephedrine can be extracted from species of this genus
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Gymnosperms
• Ginkgophytes (phylum Ginkgophyta)– Only one living species remains
• Ginkgo biloba
– Dioecious• Male and female
reproductive structures form on different trees
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• Conifers (phylum Coniferophyta) are the largest gymnosperm phylum and include:– Pines, spruces, firs, cedars and others– Coastal redwood – Tallest tree– Bristlecone pine – Oldest living tree
• Conifers are sources of important products• Timber, paper, resin and taxol (anti-cancer)
Gymnosperms
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• Pines– More than 100 species, all
in the Northern hemisphere
– Produce tough needlelike leaves in clusters
– Leaves have:• Thick cuticle and recessed
stomata• Canals into which cells
secrete resin
Gymnosperms
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Pine reproduction
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Angiosperms• Angiosperm origins are a mystery
• The oldest known angiosperm in the fossil record is Archaefructus
• The closest living relative to the original angiosperm is Amborella
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Angiosperms
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Angiosperms
• Flower morphology– Primordium develops into a bud at the end of
a stalk called the pedicel– Pedicel expands at the tip to form a
receptacle, to which other parts attach
– Flower parts are organized in circles called whorls
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Angiosperms
• Flower morphology– Outermost whorl = Sepals– Second whorl = Petals– Third whorl = Stamens (androecium)
• Each stamen has a pollen-bearing anther and a filament (stalk)
– Innermost whorl = Gynoecium• Consists of one or more carpels that house the
female gametophyte
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Angiosperms
The ovary eventually develops into the plant’s fruit
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Angiosperm Reproduction