Evolution and diversity of plants 2 PDF

Preview

Summary

notes on the evolution of plants, split into 2 parts. Pt 1...

Description

Evolution and diversity of plants 2 Week 5

Learning Objectives The Evolution of Land plants Adaptations and diversification of plants onto land  Reduce dependence on water for reproduction: extend sporophyte not gametophyte stage; and make it nutritionally independent  Increases in height (vascular tissues) to occupy new habitats ?; outcompete; evolution of “woodiness”  Spores to seeds (more resistance and dormancy, subsequent modification)  Diversification of “leaves” (water conservation, diversity of low light conditions, complex canopy)  Pollen and seed dispersal (by animals; wind); “fruits” 3 main key innovations Roots Vascular tissue (tracheids) Seeds the main difference between vascular plants and bryophytes (non-vascular plants) is the duration of the 2n phase of their lives (as seen on the diagram) 1n = gametophyte (haploid stage) this is extended in Bryophytes 2n = Sporophytes (diploid stage) this is extended in vascular plants Extended gametophyte stage (with nutritional dependence of S in wet habitats Extended sporophyte stage (and nutritional independence) in drier/seasonal habitats

A is a hypothetical algal precursor that had equal lengths of generations in its life B is a bryophyte which is forming an extended haploid gametophytes from spores released by meiosis, then forming a relatively short lived sporophyte (diploid stage) C is a Vascular plant, and has an extended diploid, mitotic period and a shortened gametophyte period. it begins with the short haploid period and undergoes gamete fusion to form the long living diploid this reduces the reliance on water for reproduction

Bryophytes Alternation of generations Spend most of life cycle as haploid (gametophyte) stage Reproduce by spores that germinate into archegonia (female) and antheridia (male) Need moisture to transmit motile sperm to egg Do not have true vascular tissue (no lignin) or roots Structures are either thalloid (like flat plates) or foliose (leafy) Liverworts: Differ from mosses in their single celled rhizoids (root-like structures, not true roots) Membrane -bound oil bodies with isoprenoids

Sperm with 2 flagellae – water needed for fertilisation Two main groups – thalloid and leafy and are almost all tropical Mosses Leaves 1 cell layer thick - no cuticle to protect them from desiccation attached to substrates with Rhizoids - no water/nutrient absorption Sporophyte gen is usually on a stalk with a capsule filled with spores spores can be projected great distances 20cm) Hornworts Gametophyte is thalloid (flat) Possibly most ancient of bryophyte lineages Unknown symbiotic relationships with cyanobacteria and with mycorrhizal fungi

Vascular plants Phloem – conducts sugars produced by photosynthesis from leaves to rest of plant allows for the a greater range of cell differentiation as cells can get their nutrients from active transport instead of having to be photosynthetic themselves Xylem – conducts water from soil to leaves where it is used in photosynthesis and transpiration; tracheids and vessel elements are lignified and extremely strong (increase height) this allows for increase in height as they are now able to force water higher through creating hidrotic pressure against the lignified walls Lycophytes

Possess microphylls – small leaves that are analogous to the megaphylls (leaves) of other vascular plants Reproduce by spores Sporophyte is the main plant body Three groups – lycopods, quillworts and selaginellas, the spores of the lycopods are highly flammable were more diverse in the past than today

Ferns and Horsetails reproduce by spores no seeds spend most of their time as sporophytes, but gametophyte is free living and photosynthetic Ferns and horsetails not thought related before DNA sequencing studies

Seed plants: Gymnosperms and Angiosperms Gnetales – once thought to be closest living relatives of flowering plants (angiosperms) Welwitschia mirabilis – Namibian desert Ephedra – worldwide – ephedrine used as performance enhancing drug, banned in USA Gnetum – tropical lianas – wood has vessel elements, not only tracheids

Angiosperms Ovules are held inside a protective structure – the carpel Carpels (ovary) develop into a true fruit Flowers and fruit facilitated the evolution of plant-animal interactions  pollination  Dispersal Xylem composed of vessel elements Dicots are not monophyletic 2 cotyledons from germinating seed flower in 5 parts ANA-grade Amborella trichopoda - Known only from New Caledonia and is the sister group to all flowering plants Trithuria – a surprising relative of waterlilies, previously thought to be related to grasses

Magnoliids often pollinated by beetles, this may be what primitive flowers looked like - pollinated by insects even before they evolved to fly

Monocots 1 cotyledon from germinating seed flower in 3 parts

human nutrition are very dependent on the 3 domesticated monocots (rice, wheat and maize) only domesticated orchid is vanilla - orchids have a very particular pollination mechanism that is hard to replicate

Eudicots Most of the species diversity of flowering plants 2 monophyletic lineages  Rosids  Asterids rosids don't have any clear shared, derived features - they share combinations of features such as separate petals asterids have a single embryo integument along with a shared combination of derived characteristics such as shared petals (tubular flowers) Bilaterally symmetrical (zygomorphic) flowers Plant-animal interactions can be mutualistic, with insects getting nectar and they move the plant's gametes around can be more complex such as the fungus gnat which visit the male flower to get the pollen, but once they reach the female flower, they get trapped and die

pseudocopulation in orchids - where flowers resemble female bees to entice male bees to try and copulate with them, taken the pollen to different orchid

 plants living on other plants, e.g. a plant colonises another plant that is taller and germinate on top of them (epiphytes)  interactions with animals such as defence, dispersal, pollination and herbivory - eating fruits and seeds are dispersed through droppings  interactions with fungi which can be pathogenic but can also be cleaning the leaves that they grow on...