evolution of land plants Flashcards
1
Q
primary endosymbiosis
A
- evolution of bacteria from anoxygenic photosynthesis to oxygenic photosynthesis by using water as an electron donor
- endosymbiotic event of ancestral cyanobacterium gave rise to green algae
2
Q
Common characteristics of embryophytes and Charophycaea
A
- embryophytes (terrestrial plants) evolved from class Charophycaea (green algae/chlorophyte)
- cellulose cell walls (unusual for photosynthesizers)
- starch synthesis and storage in stroma of chloroplast (often stored in cytoplasm of other photosynthesizers)
- chlorophyll b, lutein, beta carotein accessory pigments (unusual combination, chlorophyll a as a primary pigment is universal)
- granal stacks (more than 3 layers of thylakoid membranes, most have 1, 2 or 3)
- 2 membranes around chloroplasts (correlates to number of endosymbiotic events)
3
Q
Alternation of generations in chlorophytes
A
Diplobiontic
- multicellular haploid gametophyte produces gametes through mitosis
- gametes fuse to form diploid sporophyte, produces spores via meiosis
- spores differentiate into gametophyte
- usually indistinguishable life stages
- adapted to living in an aquatic environment, critical in invasion of land (sporophyte not water limited)
4
Q
Plant lineages
A
3 clades of green algae
- chlorophytes (aquatic, predominantly freshwater, most green algae)
- coleochaetophytes
- stoneworts/charales
5
Q
Non-vascular extant lineages
A
Bryophytes
- liverworts
- mosses
- hornworts
All included in association with water, lack vascular elements, remained small, lack true leaves, retain and protect their embryo
6
Q
Liverworts
A
- around 900 species
- lack stomata
- very thin ribbon like thallus
- rhizoids for attachment
- gametophyte dominant (haploid)
- produces archegonia (female) or antheridia (male)
- antheridia produce biflagellate sperm (mitosis), need water to swim to reach archegonia
- embryo retained, releases spores (meiosis), develop into gametophyte
7
Q
Mosses
A
- 12,000 species
- small, grow in damp habitats
- absorb nutrients across leaves
- gametophyte dominant, similar life cycle to liverworts
8
Q
Hornworts
A
- 100-150 species
- flattened thallus
- cells only have one chloroplast
- gametophyte dominant, antheridia and archegonia develop within thallus
- sporophyte retains and acquires nutrients from gametophyte via the foot
9
Q
Lychophytes
A
- club mosses
- 1,300 species
- oldest living vascular plants, early vascular elements
- dominated the Carboniferous, were over 40m tall, important in coal and fossil fuel reserves
- sporophyte is dominant stage, sperm not water dependent
- still have antheridia and archegonia
- evolution of leaves, microphylls, early not true leaves
10
Q
Euphyllophytes
A
- sister group to club mosses
- include ferns (Polypodiophyta), Psilophyton species (extinct)
- horsetails (Equisetidae), fern subclass
- macrophylls, more complex leaves
- gymnosperms and angiosperms evolved from
11
Q
Ferns
A
- 10,500 species
- fossils from 360mya, late Devonian
- produces spores, sporophyte dominant
- gametophyte stage relatively insignificant
12
Q
Horsetails
A
- 15 species
- fossils from 200mya, early Jurassic
- true leaves (reduced) and roots
- sporophyte dominant
13
Q
Spermatophyta
A
- include gymnosperms and angiosperms, seed plants
- early seed producing taxa include Pteridosperms (from Early Carboniferous, fern-like leaves produce seeds) and Cordaites (extinct)
- angiosperms thought to have arisen from seed fern lineage (Caytoniales), not gymnosperms
14
Q
evolutionary history of algae
A
- Grypania, oldest unicellular green alga, large, discovered North Michigan, dates from 1870mya (Proterozoic)
- Bangia, oldest filamentous red algae, found in Northern Canada, 1200mya
- Cladophora, oldest multicellular green alga, found in Sweden in shale rock, 800-700mya, genus still exists today
15
Q
terrestrial invasion
A
- evidence of land colonisation by mid-Ordovician (470mya)
- initially very hostile to life, several significant events occurred to allow plants to colonise land
16
Q
significant events that led up to the colonisation of land by plants
A
- intense tectonic activity led to formation of Pangea
- mantle upwelling and melting increased sea levels and caused widespread flooding
- 3 glaciation events
- lad to massive areas of very shallow sea that would continually flood and drain driving the adaptation of plants to terrestrial environments
17
Q
soil formation
A
- early land was bare rock with no available nutrients or minerals
- colonies by cyanobacteria, non-photosynthetic bacteria and eukaryotes e.g. lichen, PABs, (purple autotrophic bacteria, anoxygenic)
- acid rain (from volcanic activity) and organic acids produced by bacteria and lichen started the weathering process
- Palaeo-soils (early soils) started forming 2700mya
- soils established by 440mya
18
Q
nitrogen fixation in the soil
A
- nitrogen converted from gas into nitrate in the soil, biologically available
- cyanobacteria are the only group that fixes nitrogen, free living cyanobacteria and cyanobacteria as the photobiont in lichen
- lightning also fixes nitrogen into the soil
19
Q
Siderophores
A
- produced by microbes in response to ion deficiency
- ion chelating molecule
- allows microbes to take up Fe3+ from the environment, otherwise a very difficult molecule to take up
- iron also taken up by other microbes from the siderophores and when a microbe dies and iron is released
20
Q
climatic conditions in the Ordovician (490-440mya)
A
- high levels CO2 (0.23-1.4% higher)
- low levels O2 (4%, 20% now)
- ozone thinner, more UV radiation
- less solar radiation reaching earth
- surface temperatures lower, ~21C
- cooling throughout Ordovician resulting in a glaciation event ~460mya
21
Q
developmental specialisation, diplobiontic life cycle
A
- provided flexibility to evolve on land
- sporophyte can invade terrestrial environment and produce thousands of spores
- greater dispersal of spores, increased likelihood of spores landing in advantageous environment, speeding up evolution
22
Q
evolution of sporopollenin
A
- polymer in spores
- provides resistance to desiccation, structural rigidity and UV protection
23
Q
evolution of cuticle
A
- lipid polymers surrounding all terrestrial structures
- resistance against microbial attack and abrasion
- resistance to desiccation
24
Q
evolution of stomata
A
- not needed in high CO2, levels started to drop
- more air can enter thallus to facilitate photosynthesis
- made plant more vulnerable to dessication
25
Q
water and nutrient uptake, early evolution of supporting and conducting elements
A
- aquatic plants have no requirement for structural support or conducting elements, very simple, water and nutrient uptake occurs across whole plant
- need for supporting and conducting element in terrestrial plants when height is >2cm
- early plants used hollow dead cells with strong cell walls
- dead cells so reduced metabolic demands, increase capacity for conducting water
26
Q
evolution of strengthened cell walls
A
- water has a compressive force, so cells that conduct water need a strengthened wall so they don’t collapse
- evolved when atmospheric O2 levels rose as the production of complex carbohydrates and compounds to strengthen cell wall are metabolically expensive so require high levels of O2
27
Q
evolution of strengthened cell walls, three tracheid types
A
- G-type cell wall, annular retricular thickening (strengthened with hoops of thickened cell wall), least complex
- S-type cell wall, helical thickenings (spirals)
- P-type cell wall, scalariform pittings (ladder rungs), most complex
28
Q
evolution of mechanical support as plants got taller
A
- stem required with flexural rigidity (ability to bend), thick walled and wide
- vascular elements (hydrostatic cells) remained within centre of stem to provide strengthening
- not sufficient when plants grew taller, so migration of vascular elements to the periphery
- interference with photosynthesis, drove evolution of leaves
29
Q
anchorage, evolution of roots
A
- first fossilised roots ~408mya
- consequence of main stem being covered in mud
- growth of miniscule unspecialised projections, no root caps or epidermis
- started to specialise for anchorage and nutrient uptake, development of root caps and epidermis
30
Q
impacts of land colonisation, mid-Ordovician to early Devonian
A
- 470-400mya
- channeling or rivers and stabilisation of river banks (plants still semi-aquatic, root stabilisation)
- muddy flood plains and soil formation (organic matter inputs)
- Ordovician glaciation due to weathering of rocks, calcium and magnesium silicates washed into sea and react with C)2 to form carbonate deposits. More CO2 from atmosphere absorbed by sea, dropping global temperatures
31
Q
climate in mid Devonian to the end of the Carboniferous
A
- 394-299mya
- climate changed from warm and humid to cold and arid, CO2 levels dropped, O2 levels rose
- extensive tectonic activity
- high precipitation at the equator created large boggy areas at the equator
- tall clubmosses dominated at the equator, large backlog of lignin created massive carbon stores
- peak in number of plant species 360mya then gradual decline
32
Q
further adaptations to land
A
- 394-299mya
- increase in height (less competition, greater spore dispersal) through evolution of more complex separate vascular elements (xylem and phloem)
- optimise photosynthesis through the evolution of leaves
- eliminate reliance on water for reproduction by becoming haplobiontic
33
Q
evolution of more complex vascular elements
A
- protostele 420mya, central xylem surrounded by phloem
- siphonostele 407mya, hollow centre, pith, surrounded by xylem then phloem
- eustele 390mya, many distinct strands of xylem and phloem around the periphery (most similar to vascular bundles seen today)
34
Q
optimisation of photosynthesis, evolution of leaves
A
- compartmentalisation of photosynthesis required due to the evolution of secondary xylem and phloem (wood)
- microphylls, small leaf evolved from spines from the main stem. contain one vascular element, in plants with protosteles (less complex)
- macrophylls, large leaf, evolved from webbing forming between branches. multiple vascular elements run through leaves, plants with siphonosteles or eusteles (more complex)
35
Q
reproduction, evolution of heterospory
A
- most alga/ early land plants produce undifferentiated gametes (+ and - mating types)
- mutation resulted in the formation of two different types of spore (heterospory)
- megaspore = ancestral ovule
- microspore = ancestral pollen
- megaspore retained and encapsulated within a coat (protection against dessication)
- micropyle/hole evolved at top of seed coat to allow sperm entry
36
Q
evolution of pollen tube
A
- sperm stopped being released, remained encapsulated in pollen coat until pollen reached ovule
- in early plants, pollen would land on female plant and send out pollen tube to parasitise/obtain nutrients from female
- sperm would then be released from pollen and would enter ovule through micropyle
- evolution of pollen tube, took over delivery of sperm directly into ovule
37
Q
first tree
A
- Gilboa tree (Pseudosprochnus)
- 3385mya
- leafless photosynthetic branches that were periodically shed
- found in waterlogged low oxygen soils
- went extinct in late Devonian
38
Q
evolution in Early Carboniferous
A
- 360mya
- Sphenopsids (horsetails)
- Lycopsids (club mosses)
- Filicospids (ferns)
- Progymnosperms (extinct, gave rise to gymnospersm)
- Cordaites (extinct gymnosperms)
- Pteridosperms (extinct seed ferns)
39
Q
evolution in Permian
A
- 299mya
- significant radiation of seed plants
- Cycadales (cycads, extant gymnosperms)
- Ginkgoales (ginkos, extant gymnosperms)
- Bennittitales (bennettites, extinct)
- Glossopteridaceae (extinct)
- Gretales (extant gymnosperms)
40
Q
Permian to Triassic
A
- formation of Pangea
- climate changed to warm and humid
- atmospheric CO2 increased 300-1500ppm
- evolution of conifers, sister group to Cordaites
- evolution of Caytoniales (extinct), gave rise to angiosperms
41
Q
angiosperms
A
- first definitive fossil evidence 139mya (lower Cretaceous)
- genetic analysis (mutation rate) provided evidence they possibly evolve 140my earlier but no fossil evidence yet
- first fossils were aquatic lilies, earlier ancestors thought to be herbaceous or small and aquatic
- evolved at lower warmer latitudes alongside gymnosperms
- very rapid evolution and diversification (possibly more evidence they evolved earlier)
- pushed out gymnosperms to higher latitudes (still seen in plant distribution today)
42
Q
what drove the rapid evolution and diversification of angiosperms?
A
- conducive environment
- insects evolved alongside, main pollinators, could carry pollen further increasing genetic diversity
- dinosaurs, change in foraging from high to low foraging pushed out gymnosperms at equator?
43
Q
climate at time of rapid angiosperm speciation
A
- period of warmth from climate change and tectonic activity
- super plume event
- sea level rise
- fluctuating CO2 levels
44
Q
coevolution of angiosperms alongside insects
A
- early angiosperms insect pollinated
- zoophily, evidence of sticky pollen
- further dispersal increases heterozygosity
