Hypotheses about the origin of life. which is your favorite hypothesis and why
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PPVPlantsBryophytesandSeedlessVascularPlants2812928129.pptx
Kingdom Plantae
Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga
Charophyceans or charophytes: closest land plant ancestors
They are green algae, but are closer related to plants than other green algae as chlorophytes
Chara
Macro
Micro
Chara: A genus of complex charophyte resembling land plants
Oogonium (archegonium) with one single egg
Antheridium with sperm
Chara, sexual organs
Sex organs in Chara
Oogonium (pl: oogonia) Female flask-shaped structure containing each one egg (non motile). Covered with cell layer: multicellular sex organ.
Antheridium (pl: antheridia) Male round structure, also multicellular. Produce motile flagellated sperms
Spirogyra: Another genus of complex charophyte resembling land plants
The first plants probably originated from extinct relatives of Chara or other charophyceans
They already had similarity to plants as:
Same food reserve: starch
Same photosynthetic pigments:
chlorophylls a and b
carotenes
xanthophylls
Similar structure of flagella
Similar cell division structure
Molecular markers: rRNA indicates homology
Once the primitive plants arrived on land they adapted to new conditions of gravity, humidity, substrate, temperature.
The ones who survived transformed in land plants.
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New in true plants:
Alternation of generations
Multicellular, dependent Embryo
Walled spores produced in sporangia
Apical meristems
New in true plants: Alternation of generations
Plants alternate between two multicellular stages:
the haploid gametophyte that produces haploid gametes by mitosis
the diploid sporophyte that produces haploid spores by meiosis
In land plants this alternation of generations is heteromorphic (both stages are morphologically different); in some green algae it is isomorphic. Charophyceans do not have alternation of generations.
Alternation of generations
Plants Sexual Life Cycle
Sexual cycles in different organisms
General plant cycle
The sporophyte is the multicellular diploid generation (2n).
The sporophyte contains the sporangium (pl. sporangia), the structure specialized in producing spores (n) by meiosis.
The gametophyte is the multicellular haploid generation (n).
The gametophyte contains the gametangium, the structure specialized in producing gametes.
The archegonium (pl. archegonia) is the female gametangia, produce eggs (the female gametes).
The antheridium (pl. antheridia) is the male gametangia, produces sperm (the male gametes)
New in true plants (Embryophytes): Multicellular, dependent Embryo
Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga
Spores are also present in some protists and in fungi, but plants spores are produced in a specific structure, the plant sporangia, and are covered by sporopollenin, a durable organic material that forms a wall and provides resistance to harsh conditions.
New in true plants:
Walled spores produced in sporangia
Meristems are sites of repeated cell division of unspecialized cells. These cells differentiate, and become specialized in relation to the function they will perform.
Apical Meristems are the site of primary growth in a plant, and can be found at the root and shoot tips. Here you can find unspecialized cells, which undergo the following sequence to become a functional part of the plant
New in true plants:
Apical meristems
During the colonization of land, new adaptations appear in plants
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Bryophytes are dominated by the gametophyte stage
Bryophytes are anchored to the substrate by rhizoids. Rhizoids are not true roots.
The flagellated sperm produced by bryophytes must swim through a film of water to reach and fertilize the egg
In bryophytes, the gametophytes are larger and longer-living than sporophytes. We say that gametophyte (n) is the dominant generation
The height of gametophytes is constrained by lack of vascular tissues
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Bryophytes are represented today by three phyla of small herbaceous (non-woody) plants:
Liverworts, phylum Hepatophyta. Example: Marchantia
Mosses, phylum Bryophyta. Example: Polytrichum
Hornworts, phylum Anthocerophyta. Example: Anthoceros sp.
Liverworts, (Hepatophyta)
Worts=Herbs
Liverworts = liver-like herbs
Marchantia
The body is called thallus (pl thalli). The thallus is the gametophyte portion of the life cycle.
Asexual reproduction: gemmae in the gemma cups
Sexual reproduction:
On male plants: Anteridiophores containing antheridia
On female plants: archegoniophores containing archegonia
See pictures in your book and preserved specimens
Rhizoids (no real roots)
Liverwort, microscopic slide showing:
Cuticle
Pore (but no yet stoma)
Rhizoid (not a real root)
1 m
Thallus
(Gametophyte)
n=haploid
Gametangiophore
(archegoniophore) of a female plant
Marchantia polymorpha, a “thalloid” liverwort
Gemma cup
(asexual reproduction from the tallus, dispersed by rain)
Rhizoids
(to anchor to the substrate)
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Figure 29.9 Exploring: Bryophyte Diversity
Marchantia, sexual reproduction
Marchantia,
asexual reproduction by gemmae
Female plant
Male plant
Gemmae are splashed out of the cups by raindrops and can they grow in new gametophytes. Each identical to the parent plant that produced it by mitosis
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1 m
Polytrichum commune, hairy-cap moss
Capsule
Seta
Sporophyte
Gametophyte
Mosses (Bryophyta)
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Figure 29.9 Exploring: Bryophyte Diversity
Gametophyte
Gametophore
Rhizoids
PAGE 269
Ex. 15.4
Answer questions
LE 29-8
Male
gametophyte
“Bud”
Spores develop into
threadlike protonemata.
Protonemata
“Bud”
The haploid protonemata produce “buds” that grow into gametophytes.
Raindrop
Sperm
Antheridia
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.
Egg
Haploid (n)
Diploid (2n)
Key
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.
Archegonia
Rhizoid
Female
gametophyte
Gametophore
Spores
Sporangium
Peristome
MEIOSIS
Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.
FERTILIZATION
(within archegonium)
Archegonium
Zygote
Embryo
Calyptra
Young
sporophyte
Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
The diploid zygote develops into a sporophyte embryo within the archegonium.
Capsule
(sporangium)
Seta
Foot
Mature
sporophytes
Capsule with
peristome (SEM)
Female
gametophytes
Moss Life Cycle
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These figures are taken from the moss cycle
(preview slide)
To distinguish antheridium from archegonium, look for sterile jacket and spermatogenic tissue in antheridium.
Moss mature capsule
Seedless Vascular Plants (Tracheophytes) The First Plants to Grow Tall
Bryophytes were the prevalent vegetation during the first 100 million years of plant evolution
The earliest vascular plants date to 425 million years ago
Vascular tissue allowed these plants to grow tall
Early vascular plants lacked seeds (seedless).
Vascular Tissue
Vascular tissue: special tissues in plant that conduct water and minerals
Xylem: conducts water and minerals
Xylem conveys water and dissolved minerals upward from roots into the shoots. Dead cells make tracheids strengthened by lignin, which provide structural support
Phloem: conducts the products of photosynthesis
Phloem consists on living cells and transports organic nutrients from where they are made to where they are needed.
Seedless Vascular Plants
Have vascular tissue, specialized in water and food transport
Sporophyte (2n) is the dominant generation
Most of them have true roots, stem and leaves with stomata
Distinguish two clades:
Lycophytes: Club mosses
Pterophytes, most are Moniliophytes: Whisk ferns, horstails and ferns
Seedless vascular plants can be divided into two clades
Lycophytes
(club mosses and their relatives)
Monilophytes
(ferns and their relatives)
Figure 26.20 Lycophytes and monilophytes (seedless vascular plants)
Phylum Lycophyta:
Giant lycophytes thrived for millions of years in moist swamps
Surviving (extant) species are small herbaceous plants
Selaginella (Spike Moss) resurrection plant
Lycopodium: club mosses
Strobili (pl), strobilus (sin): region of the stem specialized in spore formation in Lycopodium (fig 15-19) Note small leaves
strobilus
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Sporophylls and Spore Variations
Sporophylls are modified leaves with sporangia
Strobili are cone-like structures formed from groups of sporophylls
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https://en.wikipedia.org/wiki/File:Rose_of_Jericho.gif
Resurrection plant
Clade Pterophytes (Monilophytes) Ferns, Horsetails and Whisk Ferns
Ferns are the most diverse seedless vascular plants, with more than 12,000 species
They are most diverse in the tropics but also thrive in temperate forests
Some species are even adapted to arid climates
Horsetails were diverse during the Carboniferous period, but are now restricted to the genus Equisetum
Whisk ferns resemble ancestral vascular plants but are closely related to modern ferns
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Psilotum (whisk ferns)
Small
Photosynthetic stems
Aerial spores
No roots, symbiosis with fungi
No true leaves
Rhizoids
whisk ferns
Equisetum (horsetails)
Clusters of leaves in nodes
Stem contains Silica
Nodes and internodes
Photosynthesis only in the stem
horsetails
Horsetail gametophytes are small and green (photosynthetic)
ferns
FERNS
Dissected leaves called fronds
Underground horizontal stem (rhizome)
Real roots
Sori (clusters of sporangia) in the undersurface of fronds
Unrolling young fronds (fiddleheads)
Abundant, with ornamental value
ferns anatomy
15-26, 15-27 ,PAGE 281
Unrolling young fronds (fiddleheads)
Underground horizontal stem (rhizome)
Real roots
Sori (clusters of sporangia) in the undersurface of fronds
15-28 ,PAGE 282
Vascular tissue
1 m
Key
Haploid (n)
Diploid (2n)
MEIOSIS
Spore dispersal
Spore (n)
Young gametophyte
Rhizoid
Underside of mature gametophyte (n)
Antheridium
Sperm
Archegonium
Egg
FERTILIZATION
Zygote (2n)
Gametophyte
New sporophyte
Mature sporophyte (2n)
Fiddlehead (young leaf)
Sporangium
Sorus
Sporangium
The life cycle of a fern
Slide 29
Slides 27,28
Living
Specimen
Check sori
See also figure 15-33, page 284
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Figure 29.13 The life cycle of a fern.
SPORES WILL PRODUCE A GAMETOPHYTE
Monoecious gametophyte
Note: Some species are diecious
(separate sex)
Fig 15-32
Fern young sporophyte
Vascular tissue in a fern rhizome (modified stem)
Vascular bundle is also present in ferns’ roots and leaves (fronds)
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