9. Plant evolution.pdf

Evolution of plants Aarni Auerniitty  Mosses (bryophytes)  Oxygen saturation reached 20 % in the atmosphere 460 million years ago  more effective ozone layer  Multicellular algae adapted to endure dry conditions in tide beaches  Mosses  Most mosses are thallophytes (sekovar...

Evolution of plants Aarni Auerniitty  Mosses (bryophytes)  Oxygen saturation reached 20 % in the atmosphere 460 million years ago  more effective ozone layer  Multicellular algae adapted to endure dry conditions in tide beaches  Mosses  Most mosses are thallophytes (sekovartinen)= leaves, roots and stem can’t be told apart  Mosses absorb water and nutrients with all their parts, primitive roots don’t reach deep into soil  humid environments required  Can hibernate over dry periods  Grow from the top forming peat underneath  Pteridophytes  Evolved around 400 mya, first vascular plants  Larger and more complex than mosses  Ferns (Polypodiopsida, saniaiset), horsetails (Equisetum, kortteet) and clubmosses (Lycopodiaceae, lieot)  Adaptations  Roots for water and nutrient intake  Leaves for photosynthesizing  Stem for support and height  Vascular tissue for transport  Thicker surface to protect from drying  Stomata (ilmaraot) for controlled gas exchange and water evaporation Cryptogam reproduction  Bryophytes and pteridophytes form the group of cryptogams (itiökasvit)  Many cryptogams cycle between asexual and sexual reproduction  Alteration of generations  Spores spread from sporangium (itiöpesäke)  Ferns form a prothallus (alkeisvarsikko) from spores where the fertilisation occurs  Gymnosperms  As climate turned colder and more arid gymnosperms (paljassiemeniset) took over pteridophytes  Key adaptations  Seed  Always sexual reproduction  Extremely durable, contains initial energy reserve for the seedling  Cuticle: waxy layer to reduce water loss  Pollen  Wind pollination, reproduction not dependant on water  Gymnosperm reproduction  Pollen formed in stamen (hede)  fertilises eggs in pistil (emi)  Seeds form on top of carpels (emilehti) and mature inside cones  Relatively vulnerable Flowering plants (angiosperms)  Evolved soon after gymnosperms, but got more numerous later  Now the most common group of plants  Key adaptation compared to gymnosperms was the flower  Developing embryo is protected by ovary  Attracting pollinators to spread pollen and seeds  Nectar and fruit Angiosperm reproduction  Fertilization occurs as pollen reaches the stigma (luotti) of pistil  Often using insects, birds or mammals as vector  A pollen tube grows from the pollen through pistil into the ovary  Double fertilization = in addition of the egg being fertilized also a polar nucleus is fertilized causing it to develop into nutrition reserve  Seeds are spread through multitude of ways  Hydraulic pressure  Hooks  Fruit  Wind  Vascular plants  Everything but algae and mosses  Water is transferred from soil through roots, stem and leaves  Root hairs increase area of roots  Osmosis helps water get absorbed --> root pressure  Transpiration pull through stomata  Pulls the water pillar through the plant  Capillary action (water cohesion and adhesion) in the thin tubes of xylem helps water travel against gravity  Vascular bundles in vascular tissue are used in transportation  Xylem transports water and nutrients (tracheids/vessels), phloem products from photosynthesis (sieve tubes)  Woody plants widen through growth in vascular cambium (between phloem and xylem)