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Diversity of Plants Features of plants • Photosynthetic with Chlorophylls a and b and carotene accessory pigment • cellulose cell walls • carbohydrate storage as starch in chloroplast • Chloroplast structure organised into grana • mechanisms to protect the zygote Evolution of plants • Evolution is driven by the need to absorb, transport and retain water, and the need to reduce the requirement of water for fertilisation. Groups of plants • The non-seed, nonvascular plants Mosses, Liverworts and Hornworts • The non-seed vascular plants Whisk ferns, Club mosses, Horsetails, Ferns • Gymnosperms • Angiosperms Mosses, Liverworts and Hornworts • Important today both ecologically and economically • peat-burning provides part of Ireland's energy requirements, and unlike fossil fuels, peat is a renewable resource when properly managed. • In addition, peatlands are the habitat of commercial crops such as blueberries and cranberries. • Important in horticulture for potting and as a soil additive • First colonisers of bare land • • • • • • • • Mosses, Liverworts and Hornworts No leaves No vascular tissues No true roots Poorly defined cuticle flagellated spores (sperm) Gametophyte dominant Sporophyte on gametophyte Hornworts have a long lived sporophyte • Liverworts have a lobed thallus Life cycle Spores produced by meiosis Fertilisation of egg gives Diploid sporophyte which then divides to produce a stalk and capsule Archegonium gives single egg cell by mitosis Sperm Antheridum gives sperm by mitosis Spore (n) Female gametophyte Male gametophyte Protonoma Development of Moss from the protonoma Moss spore Early protonema Developing moss plant Moss reproductive structures Archegonia with egg cell Antheridia give flagellated sperm Non-seed, non-vascular plants and water • Capillary uptake of water, sufficient only for a few centimetres, restricts the height of the plant. • All parts of the plant must photosynthesise as no phloem to transport sugars - no subterranean roots. • Abundant water needed for germination and growth of the protonema • Need a film of water for the sperm to swim in for fertilisation Seedless vascular plants • All have phloem and xylem in the stem to transport sugars and water (tracheids only) • All have underground stem (rhizome) • All have essentially the same reproductive system with a dominant sporophyte • • • • Whisk Ferns Club mosses horsetails ferns Whisk Ferns (Psilophytes) • No true leaves, but expanded surfaces without vascular tissue (enations) - restricts the length of the enations. Club mosses (Lycophyta) • Microphylls (leaves with a single unbranched vascular bundle). Leaves may be long but not wide. • Now rare, but in past times, tree-form club mosses more than 35 metres tall were abundant Horsetails • Microphylls (may be more than one parallel vascular bundle) means leaves may also be wider. • Only one genus Equisetum survives today although in carboniferous times, they were abundant and tree-sized. Ferns • Megaphylls (leaves with branched vascular bundles). Leaves may be any size or shape. Life cycle • • • • Spore bearing leaves (sporophylls) produce Spore-producing structures (sporangia) Spores produced by meiosis Sometimes two different sizes of spores, microspores and megaspores giving male and female prothalli, are produced from microsporangia and megasporangia. This may explain how seeds originated. Life cycle of Whisk ferns, Club mosses, Horsetails and Ferns Spores produced by meiosis Spores germinate to give protonema N Sporophylls Archegonia develop on the prothallus Sperm released Antheridia develop on the prothallus Mature plant is sporophyte 2N Protonema germinates into a heart shaped prothallus Water and non-seed vascular plants • Phloem allows underground, nonphotosynthetic parts which provide anchorage and take up water. • Xylem allows the plant to grow to a great height. • Plants need water for growth of the protonema/ prothallus. • Need a film of water for the sperm to swim in for fertilisation Gymnosperms Gymnosperms • Heterospory - male and female spores are different • Retention and protection of the female spores • Pollination • Seeds (born naked) • Well developed roots • • • • 4 subgroups Conifers Cycads Gnetophyta – Gnetum – Welwitschia – Ephedra • Gingkgophyta – Ginkgo biloba Seeds may have evolved by a megaspore not being shed Microsporangium gives microspores (pollen) Megaspore not shed and germinates on the plant. Megasporangium 2n gives a megaspore (n) Sporophylls Protonema germinates into a heart shaped prothallus Mature plant is sporophyte 2N Archegonia develop on the prothallus Reproduction in the gymnosperms nucellus (2n) = megasporangium Sporophyll (2n) Seed bearing scale leaf (lots of these make up a cone) Female gametophyte (n) = female prothallus = archegonium (n) Ovule = egg (n) Integuments (2N) Protective covering derived from parent (gives seed coat) Micropyle (opening to allow fertilisation) Angiosperms • Flowers • Fruits (seeds not born naked) • Endosperm • Xylem vessels • Split into two subgroups • Monocotyledons • Dicotyledons Differences between monocots and dicots Monocot Dicot Venation Parallel Reticulate Cambium Absent from bundles One Present Cotyledons Two Seed storage Endosperm Cotyledons Roots Tap root Fibrous Flower parts 3’s 4’s and 5’s Monocotyledons Families within the monocots • • • • Palms arums agaves, amaryllids, bromeliads (pineapple) • yams • grasses, sedges, cattails • • • • Irises lilies orchids gingers and bananas Orders within the Dicotyledons • Magnoliids (Primitive flowering plants) • sunflowers, scrophs, potato • Ericads (Blueberries, etc.) • "Lower" Hamamelids (Sycamores, etc.) • "Higher" Hamamelids (Oaks, Figs, Elm, etc.) • Ranunculids • Rosids (Roses, Legumes, etc.) Reproduction • Essentially the same as • Double fertilisation gymnosperms except – normal fertilisation to give a zygote that efficient vectored – fertilisation with 2 pollination. polar nuclei gives • Growth of a long endosperm pollen tube to deliver • Developing zygote the male gametes. occurs within the • Fertilisation occurs enclosing sporophyte soon after Pollination tissues - fruits