Block 6 - Plant diversity Flashcards
What are viridiplantae?
Green plants
- mostly freshwater or terrestrial
- chlorophylls a and b
- store starch inside chloroplasts
- flavonoid pigments
- 2 whiplash flagella
- Two-life history phases
What is Life cycle 1 (haplontic)?
Green algae
- Diploid phase = sporophyte (zygote only)
- Meiosis in zygote = spores
- Haploid phase = gametophyse
- Mitosis = gametes
What is Life cycle 2 (diplontic)?
Vertebrates
- Mitosis in zygote = multicellular diloid phase = a distinct generation
- Meiosis = gametes
- Haploid phase (gametes only)
- Typical life-cycle of animals
What is Life cycle 3 (haplodiplonic)?
Land plants
- Mitosis in zygote = multicellular diploid phase ( sporophyte)
- Meiosis = spores
- Haploid phase (gametophyte)
- Mitosis = gametes
- Typical of land plasnts (haploid and diploid phases in distinct generations
What are the stages in the origin of land flora?
1) Non-motile egg (oogamy) retained by mother gametophyte (n) - zygote (2n) dispersed
2) zygote (2n) retained by mother gametophyte (n)
3) Meiosis delayed - mitoses -> multicellular sporophyte (2n)
4) Closer physiological relationship of multicellular sporophyte (2n) with mother gametophyte (n)
5) Cuticle prevents dehydration on land
6) Further elaboration of sporophyte (vascular tissue)
7) Significant terrestrial spore disperal
8) Four lineages evolve:
- Liverworts - bryophyte (non-vascular)
- Mosses - bryophyte
- Hornworts - bryophyte
- Vascular plants (all other land plants)
What is the adaptive significance of the sporophyte?
- More spore mother cells
. more meioses and more spores - More meioses means:
. increased recombination potential (more variablilty)
. increased ecological amplitude (better colonising) - More spores means:
. more dispersal events
. more gameotophytes
What are charophytes?
Freshwater green algae
Diverged a long time ago from embryophytes (land plants)
Copy and paste of revision aid 1
Green plants (Viridiplantae): mainly fresh water and terrestrial, starch in chloroplasts, 2 life history phases, chlorophyll a & b, two whiplash flagella
Three life cycles: haplontic (green algae), diplontic (vertebrates), haplodiplontic (land plants)
Transition to land : Oogamy (large egg, small motile sperm), retention of zygote in archegonium, delay in meiosis (allows sporophyte development), cutinised sporophyte (wax/suberin to stop water loss), thick walled-spores promote dispersal by wind and protect cells from mechanical damage and UV-B radiation.
Elaboration of sporophyte (larger) allows greater spore dispersal
More meiosis & more spores, increased recombination potential and ecological amplitude, important for colonisation. More dispersal events, more gametophytes – more gametes.
Streptophyte lineage distinguished from chlorophyte algae by asymmetric biflagellated sperm, phragmoplast, plasmodesmata.
Charophytes (stoneworts, eg. Chara) = sister lineage to Embryophytes (land plants)
Plasmodesmata: fine strands of cytoplasm that extend through pores in the cell wall, improves cell-to-cell communication
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First land plants bryophyte-like (liverworts, mosses, hornworts), paraphyletic
Haploid dominant life cycle (non-vascular plants)
Liverworts have elators to aid spore dispersal, mosses have peristome ‘teeth’ to regulate dispersal, hornworts have multi-celled elators
Antheridia produce biflagellate sperm, released into water and swim to archegonium containing single egg cell. Zygote and embryo retained in archegonium
Bog moss (Sphagnum) wet microclimate, pioneer vegetation, important carbon sink!
Vascular plants (tracheophytes): sporophyte dominant = lycophytes (eg clubmosses), monilophytes (ferns and horsetails) and spermatophytes (seed plants) – taller to allow greater spore dispersal.
Lycophytes: simple vascular system (protostele), bear sporangia, biflagellate sperm.
Monilophytes: sporangium annular thickenings promote spore dispersal, spores have elators, sperm multiflagellate.
Tropical carboniferous forest (~ 350 Mya): dominated by tree forms of lycophytes (eg Lepidodendron), ferns & horsetails, covered much of what is currently Northern hemisphere – resulted in major coal deposits.
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Seed plants (spermatophytes) = gymnosperms and angiosperms
Seed habit - protection for embryo (young sporophyte), dispersal of sporophyte by animals, wind and water (only spores are dispersed by wind in non-seed plants); longevity through seed dormancy.
Fertilisation in enclosed female structures (ovules) retained on the sporophyte; does not need external water.
Seed plant synapomorphies: ovule (seeds), pollen
Ovule = integumented megagametophyte (haploid)
Seed coat = develop from integuments (diploid)
Pollen = endosporic microgametophyte (haploid)
Gymnosperms (naked seeds): 4 lineages = Cycads, Ginkgo, Conifers and gnetophytes
Only Cycads & Ginkgo release motile sperm (multiflagellate) from pollen grains
Conifers & gnetophytes have non-motile sperm (lost flagella) delivered by a pollen tube
Conifers: pollen wall (exine) usually has air bladders (for buoyancy)
Conifers: ecologically dominant in northern cold-temperate zone (Boreal forest /Taiga)
Conifers: high economic value in construction & paper industries
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Angiosperms (covered seeds): greatest species diversity of all plants
Reasons for success: close relationship with animals (co-evolution)
- pollination (by animals in most cases)
- fruit dispersal (by animals in some cases)
- biochemical defenses (against herbivores)
- Self-incompatibility (promotes outbreeding)
Synapomorphies: xylem vessels, flowers, carpels & fruit, tectate pollen wall, double fertilisation (endosperm)
Xylem vessels (open-ended tubes) – faster conduction (compared with tracheids) to supports rapid growth
Carpel = stigma, style & ovary
Ovary = region of carpel enclosing ovules (carpels often fused = compound ovary)
Fruit – develops from ovary wall
Double fertilisation produces a diploid zygote and a triploid endosperm (nutritive)
Monocots: single seed leaf, parallel leaf veins, complex vascular bundles, floral organs in 3’s, fibrous root system
Eudicots: two seed leaves, leaf veins branched, vascular bundles in a ring, floral organs in 4’s or 5’s, tap root usual
