plant evolution & diversity. i. kingdom protista: algae & protozoa 1. simple eukaryotes –...
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Plant Evolution & Diversity
I. Kingdom Protista: Algae & Protozoa
1. Simple Eukaryotes – mostly single-celled
Amoeba, slime molds, euglenoids, algae
2. Organisms in this Kingdom don’t fit
clearly into what we call plant, animal, or
fungi.
3. Most diverse eukaryotic Kingdom
(>60,000 species).
4. We are interested in this Kingdom because
of the Chlorophytes & Charophyceans – green
algae.
A. Characteristics
The line between Kingdom Protista and Kingdom Plantae is still being discussed……
Fig 29.4
II. Plant Origins
B. Suspects and Evidence
a. Mostly freshwater, but some are marine.
b. Have plant-like chloroplasts.
c. There are unicellular and multicellular forms
d. Can live symbiotically with fungi as lichens
1. Characteristics of Green Algae - Chlorophytes
Volvox - freshwater
Caulerpa - intertidal
Ulva – sea lettuce
Fig 28.30
2. Characteristics of Green Algae - Charophyceansa. fresh water pondsb. They are considered to be the closest ancestors oftrue plants. Evidence: i. Both have same type of cellulose-synthesizingcomplexes in cell membrane ii. Both have peroxisomes for enzyme storage iii. Both have same type of flagellated sperm iv. Both form a cell plate during cell division v. Genetic evidence – charophyceans share agreater % of similar DNA with true plants than anyother algae
III. Plants Shared CharacteristicsA. Plants are multicellular eukaryotes that are
photosynthetic autotrophs.
B. Shared pigments
C. Cellulose cell walls
D. Store glucose as starch
E. Etc.
IV. What challenges did plants face when they “moved” onto land?
A. Issues Faced 1. Acquire, transport, and conserve water 2. Protect from UV radiation 3. Resist pathogens (bacteria) and herbivores (later) 4. Others?
Then why move onto land?B. Advantages 1. 2. 3. 4.
3. Walled spores produced in sporangia
4. Multicellular gametangia
C. Adaptation to life on Land:
1. Apical Meristems
2. Alternation of generations
5. Multicellular, dependent embryos
1. Apical Meristems – localized regions of cell division at tips of roots and shoots
2. Alternation of Generations
a. 2 multicellular life stages:i. Sporophyte:
* Diploid* Divides by meiosis to form spores* Spores – haploid cells that can grow into anew, multicellular, haploid organism (thegametophyte) without fusing to another cell.
ii. Gametophyte: * Haploid* Divides by mitosis to form the gametes (eggand sperm)
b. Egg & sperm fuse to form the diploid zygote, which divides by mitosis to form the sporophyte
3. Walled spores produced in sporangia
a. Sporopollenin protects the spore from harsh environmental conditions
b. Sporangia = an organ within the sporophyte that produces the spores
c. Sporocytes = the diploid cells within the sporangia that divide by meiosis to form the haploid spores
sporocytes
4. Multicellular gametangia
a. Gametangia = multicellular organs within the
gametophyte that produce the gametes by mitosis.
b. 2 types of gametangia:
i. Archegonia – produce eggs
ii. Antheridia – produce sperm
c. Sperm travel to the egg, fertilizing it within the
archegonia.
5. Multicellular, dependent embryos
a. After fertilization, the zygote remains
within the archegonia, gaining nutrients for
growth from the gametophyte.
b. Zygote divides by mitosis to become the
sporophyte.
6. Other examples of adaptations to life on land: (not all plants have the following):
a. Cuticle – waxy covering to prevent desiccation & microbial attackb. Secondary compounds – odors, toxins, tastes, etc. toattract pollinators and defend against herbivoresc. Roots - absorb water and minerals from the soil d. Shoots - stems and leaves to make food. e. Stomata – openings in the leaf surface to allow gas exchange for photosynthesis and to regulate water loss.
f. Lignin in cell walls to provide structural support for
shoots
g. A vascular system that transports food & water from
roots to shoots and vice versa.
V. Plant Phyla
Fig 29.7
A. Nonvascular Land Plants: Bryophyta1. Characteristics a. Earliest land plants b. Phyla: Hepatophyta – liverworts,Anthocerophyta – hornworts, and Bryophyta –mosses c. Inhabit most environments, including extremes d. Peat moss (sphagnum): doesn’t decay rapidly, stores 400 billion tons of carbon e. Gametophyte is the dominant generation:
Fig 29.8
2. Moss life cycle
a. Hepatophyta – liverworts
3. Bryophyta Phyla
b. Anthocerophyta – hornworts
c. Bryophyta - mosses
Peat bogs – d. sphagnum moss (stores carbon, doesn’t decay, fuel source)
Fig 29.10
B. Vascular Plants 1. Characteristics
a. Vascular tissue Xylem = water & mineral transport and Phloem = food (carbohydrates) transport
b. Dominant generation = sporophyte
c. Sporophytes branched, independent of gametophyte parent
2. Groups
Tiny gametophytes living just above or below soil surface
Egg & Sperm need moist environment to fertilize (similar to bryophytes)
a. Seedless Vascular Plantsi. Characteristics
b. Two phyla of seedless vascular plants:
i. Phylum Lycophyta (Club Mosses) They diverged first from bryophytes with an unbranched
vascular system, flammable spore clouds, and were tree-like in the Carboniferous period
ii. Phylum PterophytaWhisk ferns – no true leaves or roots
Horsetails – hollow air-filled stems (adaptation to water-logged,
low O2 environment)
Ferns – produce clusters (sori) of sporangia on underside of
leaves (fronds)
Phylum Lycophyta: club mosses, spike mosses, quill warts
Phylum Pterophyta: ferns, horsetails, whisk ferns
Fig 29.12
c. Fern Life Cycle
d. Factors forest changes of the Carboniferous period (290-360 mya)
i. Lycophytes (tree-like) & Pteridophytes
ii. First forests
iii. Swampy forests – slow decay in low O2, formed
deep layers of organic matter
iv. Heat + pressure + time => coal
v. Pulled lots of CO2 out of atmosphere, cooling the
earth & forming glaciers
vi. Larger species died out when climate became
drier
3. Terrestrial Adaptations of Seed Plants a. Seeds replace spores as main means of dispersal.
i. Why? ii. More resistant to harsh environ b/c multicellulariii. old way (ferns & mosses) = spores released fromsporangia to disperse and develop into gametophytes iv. new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophytedevelops within the spore.
v. ovule = female sporangium + female spore. Female gametophyte develops within the spore &produces eggs. vi. after fertilization, the ovule becomes the seedvii. seed = sporophyte embryo + food supply (matureovule tissues)
Similar to Fig 30.2
b. Reduction of the gametophyte:
i. Old way: sporangia spores bisexual gametophyte
(antheridia sperm, archegonia eggs)
ii. New way:
Megasporangia megaspores female gametophyte eggs
Microsporangia microspores male gametophyte
sperm
c. Heterospory – separate male & female gametophytes
d. Ovules and seed production i. Megasporangia protected by layers of tissue
called integuments.
ii. Ovule = integuments, megasporangia, &
megaspore
iii. Megaspore female gametophyte egg &
food supply
iv. After fertilization, embryo develops, ovule
becomes a seed
Fig 30.3
e. Pollen & Pollination i. Microsporangia microspores male
gametophyte sperm
ii. Pollen = male gametophyte
iii. Pollination = transfer of pollen to ovule by wind
or animals
iv. Pollen tube brings sperm to egg within the ovule
4. Two types of seed plants: a. Gymnosperms i. Characteristics Evolved first and “Naked seed” – seeds develop on surface of specialized leaves called sporophylls
ii. Four phyla:Ginkophyta – only Ginko bilobaCycadophyta – Cycads (look like palms)Gnetophyta – Gnetophytes (tropical trees)Coniferophyta – Conifers – cone-bearing trees
Dominate forests of the N. hemisphereMost are evergreenNeedle-shaped leaves to reduce water loss during
drought
Phylum Cycadophyta
Phylum Ginkophyta
Phylum Gnetophyta
Phylum Coniferophyta
Fig 30.6
iii. Gymnosperm life cycle
b. Angiosperms i. CharacteristicsFlowering plants, Most diverse, and Evolved from gymnosperms: Sporophylls rolled together to form ovaries.
ii. One phylum: Anthophyta
Seeds are enclosed in the moist reproductive tissue of the
sporophyte generation (Ovary).
More insects and animals for pollination, less dependent
on wind.
Formerly only 2 classes: monocots & dicots. Now 4
clades (evolutionary lines):Basal angiosperms, Magnoliads, Monocots, & Eudicots
iii. Evolutionary success of Angiosperms
Increased water transport efficiency due to
improvement in xylem tissue: tracheid cells, fiber
cells, vessel elements (gymnosperms only have
tracheids)
Flowers – attract pollinators
Fruits – many forms for variety of dispersal
mechanisms
Fig 30.3iv. Angiosperm life cycle
Notice the triploid stage!Each pollen grain (male gametophyte) produces two spermSperm travel down the pollen tube & into the ovule.Double fertilization – one sperm unites with the egg to form the 2n zygote, other sperm unites with the two nuclei of the female gametophyte to form a 3n endosperm – becomes food for the developing embryoOvule matures into the seed – contains sporophyte embryo & endosperm (food).Ovary (female sporangium tissues) matures into the fruit.
Fig 29.8
Moss life cycle
Fig 29.12
Fern life cycle
Fig 30.6
Gymnosperm life cycle
Fig 30.3
Angiosperm life cycle
VI. Kingdom Fungi
Fungi were once included in the plant kingdom because they produce spores, have cell walls, and are not animals.
A. Characteristics
1. Their cell walls do not contain cellulose
(like plants), but do contain chitin
(like insects, arthropods).
2. Their bodies are filamentous.
3. The organization of large structures such as
mushrooms and morels is completely different from plants.
4. They are heterotrophs (acquire nutrients by absorption).
Hence the boot!!
B. Fungal life cycle
C. Ecological Roles of Fungi:1. Decomposers – absorb nutrients from dead
organic matter, thereby decomposing it. Recycle
nutrients to the soil.
2. Parasites – absorb nutrients from living hosts.
ex. pathogens on crops
3. Mutualists with plants – absorb nutrients from host, but
aid host in mineral uptake from soil. ex. mycorrhizae
1. Molds: rapid growing, asexually reproducing fungi2. Yeasts: single-celled fungi inhabiting moist habitats.
Raise bread & ferment alcohol
C. Lifestyles of Fungi
3. Lichens: symbiotic association of cyanobacteria or green algae and fungi.
a. Fungus provides shape b. Algae provides food, N to the fungus c. Lichens are very sensitive to air pollution; used as indicators of air quality.
4. Mycorrhizae: mutualistic association of plant roots and fungi.
a. Fungus increases the absorptive surface area of roots, increasing water and potassium uptake
b. Fungus receives food from the root exudates.
2 down and 7 to go!!