University of Louisiana at Lafayette
Popular in Evolutionary Biology
Popular in Science
Joseph Merritt Ramsey
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This 15 page Class Notes was uploaded by Lauren Notetaker on Friday April 1, 2016. The Class Notes belongs to EBIO 1010 - 02 at Tulane University taught by Bruce Fleury in Spring 2016. Since its upload, it has received 17 views. For similar materials see Evolutionary Biology in Science at Tulane University.
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Date Created: 04/01/16
Kingdom Plantae Plants are more like us than you might think Superficially, they look nothing like us There are fundamental differences between plant and animal cells There are fundamental differences in the way plant and animal bodies are designed Animals are very different from one another The basic structural design of plants, however, is remarkably consistent Plants differ mainly in subtle aspects of their metabolic chemistry Like animals, plants are descended from the protists Unlike animals, however, plants evolved from autotrophic protists So plants have a slightly different set of priorities - they don’t need to worry about where there next meal is coming from All multicellular organisms share a common set of evolutionary problems. The differences we see between them result from the different evolutionary strategies they have used to solve those problems know how to be a plant! Three fundamental modes of existence Sessile (Attached) or Motile Aquatic or Terrestrial Small or Large Sessile (Attached) or Motile Plants are all sessile organisms (tumbleweeds to the contrary) Like sessile animals, plants can stay in one place and feed Like sessile animals, plants need no central nervous system, or any nerves at all for that matter, mostly chemical response to stimuli Problem: Can’t escape danger Solution: Defend yourself (thorns, chemicals) Problem: How to reach your mates? Solution Motile sperm Problem: How to disperse your young? Solution: Motile dispersal stage (spores, seeds) Primitive plants are dispersed by spores Spores are haploid cells that can develop directly into adult plants Plant spores are protected by an outer layer of sporopollenin, a tough biopolymer that prevents dessication and other hazards Spores are incredibly small and light, easily dispersed by wind, water, animals Higher plants evolved seeds Seeds are protected by a tough seed coat Seeds are dispersed by wind, water, animals Fruits attract animals to disperse seeds Problems: Can’t escape danger How to reach your mates? How to disperse your young? Solutions: Defend yourself (thorns etc.) Motile sperm Motile dispersal stage (spores, seeds) Aquatic or Terrestrial Like animals, plants made the transition to land early in their evolutionary history But plants got there first! First land plants ~ 430 - 450 mya, looked more like upright algae, no roots, stems, or leaves Plants reshaped the surface of the Earth, preparing it for the subsequent invasion of animals (~ 350 - 400 mya) Roots of first plants held the soil in place Their organic remains created fertile soil, rich in organic materials for bacteria, fungi, invertebrates Plants provide shelter for animals from bad weather and predators Plants provide safe places for animals to build nests, and raise your young Most important producers in almost all ecosystems - a primary source of animal food Transition posed new problems that both plants and animals had to solve Solutions to these problems required a radically different set of evolutionary adaptations Problems posed by the transition from water to land Desiccation Gravity Excretion Desiccation Problem: Tissues dry out More serious problem for plants Plant tissue is cheaper to build, most of the center of the plant cell is filled with water Water is an essential ingredient in photosynthesis Remember photosynthesis? *Spores and seeds keep embryos from drying out before they can germinate *Sexual structures encased in a jacket of protective cells to keep them from drying up - antheridia and archegonia Problem: Tissues dry out Solution: Develop a protective epidermis – cover it with a waxy cuticle, bark Protect embryos (spores, seeds) Problem: Need moisture to exchange gases Solution: Cuticle keeps moisture inside - but now you need breathing holes through the cuticle to exchange gases (stomata/guard cells) Problem: Can no longer rely on external fertilization in water Solution: Internal fertilization - sperm swims to the egg, pollen grain flies through the air Primitive plants, like green algae, have motile sperm, sperm must swim to the egg Primitive plants (mosses, ferns) are restricted to moist environments Seed plants rely on pollen grain (= airborne sperm), carried by wind, animals Problems: Tissues dry out Need moisture to exchange gases Can no longer rely on external fertilization in water Solutions: Develop a protective layer of epidermal cells – cuticle, bark Protect embryos (spores, seeds) and sexual structures Keep moist surfaces inside (breathing holes) Internal fertilization, motile gametes Gravity Problem: You can no longer rely on the natural buoyancy of water Solutions: Root-shoot system of plants Roots anchor plants in the soil, shoots are stiffened stems - hold solar panels to the sky Stem stiffener is lignin, traces in fossil plants back to ~ 400 mya (Silurian) Excretion Excretion is not a problem for plants - Why? Waste products of photosynthesis? Oxygen and water! Complex metabolic chemistry of plants produces many toxic organic compounds, called secondary metabolites These secondary metabolites are mainly toxic to animals, but not to plants Plants have turned their metabolic wastes into a sophisticated chemical defense system Retain toxic compounds to keep animals from nibbling on them Many common drugs are plant byproducts, secondary compounds such as phenols and alkaloids Alkaloids include psychotropic drugs like mescaline Small or Large Problem: Small organisms can rely on diffusion to move materials in and out Diffusion is too slow for large organisms, interior cells would starve or poison themselves in their own wastes Allometric relationship: Surface area of a sphere = 4 π r 2 3 Volume of a sphere = 4/3 π r Solutions: Be very thin or very flat - leaves are flat extensions of the epidermis = big surface area for photosynthesis Develop a vascular system - tubes to carry materials back and forth (xylem & phloem) Vascular plants are called tracheophytes (= tube plants) Drinking tubes called tracheids Found in earliest fossil land plants Angiosperms also have more advanced xylem cells called vessels All tracheophytes have tracheids (including angiosperms) Vessels found mostly in angiosperms, lacking in gymnosperms and more primitive plants Vessels probably evolved independently several times (gnetophytes ex.) Primitive plants rely on diffusion - keeps them small Root - shoot system also imposes limits Must move water and minerals up from roots Must move sugar from leaves to stem and roots Leaves must get water from the roots to photosynthesize Water enters by osmosis (pressure) Water tension gets higher as the column of water gets higher, works against osmosis 2 360 ft. tree would have water tension = 180 lbs/m Too high for osmosis, so no tree could be taller than ~ 420 ft. Tallest tree ever measured was a Douglas Fir at 415 ft.! Plants have a size-related problem not shared by animals Many of the things plants need for respiration and photosynthesis are dilute or in short supply Carbon dioxide (~ 0.03% of atmosphere), phosphorous, nitrogen, water vapor, must be exchanged across surface of leaf and root Plants need a huge surface area to volume ratio to function Invest lots of energy in thin sheets of tissue, so cells are 99% water vacuoles (cheap…) So plants have met and solved many of the same environmental challenges faced by animals, and have even devised many of the same basic solutions, like a vascular system and internal fertilization. Plants have one unique characteristic, something they do not share with animals - alternation of generations Multicelluar haploid phase alternates with multicellular diploid phase (haplodiplontic) Only the green, red, and brown algae show a similar life cycle moss, fern, pine, flower diagram to label; life cycle of one of those; comes out of lab manual Alternation of Generations Haploid adult (1N) is called a gametophyte Gametophyte makes gametes by mitosis Gametes fuse into a diploid zygote (2N) Diploid adult 2N) is called a sporophyte Diploid zygote develops into an adult sporophyte Sporophyte makes haploid spores (meiosis) Spores grow into adult gametophytes In animals, the gametes fuse directly into a zygote, after a very brief free-living existence In fungi, the gametes (nuclei) never leave the hyphae, linger for a while, then fuse In plants, the gametes grow up into fully functional organisms! You might run into your sperm on the quad! What if you didn’t get along with your eggs? What’s the proper etiquette for dining with your gametes? Is casual dress okay? What would your parents say if your gametes were getting better grades than you were?? Having two distinct stages in your life cycle means natural selection can act differently on each stage (like caterpillars & butterflies) In many plants, the sporophyte (spore plant) and gametophyte (gamete plant) don’t resemble one another at all, feed in different ways, live in different places As we move up through the plant kingdom, the dominant phase gradually shifts In primitive plants the gametophyte is the dominant stage In higher plants the sporophyte is the dominant stage In very primitive plants like mosses, the leafy green plant we see is the gametophyte The sporophyte is the little brown stalk that sticks out of the top In flowering plants, the bushy green plant we see is a sporophyte Gametophyte is reduced to a few cells Female gametophyte is permanently buried in the tissues of the sporophyte Male gametophyte reduced to pollen grain Gametes are produced in a gametangium (-ia) Gametes must fuse together to develop into a diploid adult Spores are produced in a sporangium (-ia) Spores develop directly into haploid adults Gametangia that make sperm cells look different than those that make egg cells Agametangium that produces sperm is called an antheridium (-ia) Agametangium that produces eggs is called an archegonium (-ia) In primitive plants, its hard to tell one spore from another = homosporous In higher plants, male and female spores look different = heterosporous In heterosporous plants, female spores are much larger than the tiny male spores As a general rule in botany, big and bold is female, wimpy and nondescript is male (sorry guys!) Spores are formed by meiosis in special structures called sporangia Sporangia are often attached to special modified leaves called sporophylls Sporophylls (“spore leaves”) are often organized into a club-shaped strobilus (-i) Pine cones and flowers are complex variations on primitive strobili Kingdom Plantae Plants share a common ancestor with green algae Viridiplantae – new clade that includes both green algae and land plants We will use rather than Viridiplantae Land plants evolved from green algae Both have cell walls made of cellulose Both have chlorophyll a and b Both have alternation of generations Both store glucose as starch Last common ancestor for plants and algae was ~ 1 billion years ago Split algae into two lineages – marine (most chlorophytes) and fresh water/terrestrial (charophytes/land plants) Green algae - 7,000 species, fr. Greek chloros = green – Chara, Chlamydomonas, Spirogyra, Volvox Ancestral to green plants Chara is closely related to land plants Large (up to 4 ft.), branched form of fresh water algae Often called stoneworts because they can acquire a coating of calcium carbonate Spirogyra has spiral chloroplasts Pyrenoids - small circular areas on the chloroplasts where starch is manufactured Sexual reproduction by conjugation - fusion of nuclei from adjacent strands Several colonial forms, like Volvox Volvox colonies contain 500-60,000 cells Colonial organisms show specialization of cells division of labor communication between cells Volvox colony has polarity, head and tail end Special reproductive cells at tail end Flagella from surface cells cause colony to spin clockwise as it rolls along Daughter colonies form inside parent colony Parent colony must burst to release them Single-celled organisms are immortal Specialization means certain cells must die so that other cells can live Price of multicellularity is death!! Classification of Plants Plants are divided into 12 major Phyla You will only need to learn these 12 phyla, and two classes of flowering plants - and that’s it for the taxonomy! Plants are grouped together under two main criteria - whether or not they have vascular tissue, whether or not they have seeds PLANTAE = Green algae + land plants BRYOPHYTES - No vascular tissue TRACHEOPHYTES - Vascular tissue a) Non-Seed Plants (Ferns andAllies) b) Seed Plants 1. Gymnosperms 2.Angiosperms BRYOPHYTES - No vascular tissue Phylum Bryophyta - Mosses (Mnium) Phylum Hepaticophyta – Liverworts (Marchantia) PhylumAnthocerophyta - Hornworts (Anthoceros) TRACHEOPHYTES - Vascular tissue a) Non-Seed Plants (Ferns andAllies) Phylum Psilophyta - Whisk Ferns (Psilotum) Phylum Lycophyta - Club Moss, Quillworts Phylum Sphenophyta - Horsetails (Equisetum) Phylum Pterophyta - Ferns (Polypodium) b) Seed Plants 1. Gymnosperms Phylum Cycadophyta - Cycads Phylum Ginkgophyta - Ginkgo biloba Phylum Gnetophyta - Gnetum, Welwitschia Phylum Coniferophyta - Conifers (Pinus) 2.Angiosperms PhylumAnthophyta - Flowering Plants Bryophytes Plants are divided into two large groups Bryophytes - lack vascular tissue Tracheophytes - have vascular tissue Bryophytes not closely related Phylum Bryophyta - mosses Phylum Hepaticophyta - liverworts PhylumAnthocerophyta - hornworts Bryophytes share several primitive traits Rely primarily on diffusion Limited to moist environments Lack a true root-shoot system Sporophytes are not free living Bryophytes rely on diffusion to take in water and to exchange gases Bryophytes are usually small - inconspicuous Advantage of being small - don’t have to invest in support structures and vascular tissues Bryophytes have a central strand of primitive vascular tissue Not true vascular tissue, much simpler than that of higher plants Bryophytes are limited to moist environments - no mosses in the desert Bryophytes need water to reproduce - sperm must swim to the egg Bryophytes lack a true root-shoot system - no “true” roots, stems, leaves Have more primitive tissues that function like leaves, roots Tiny “leaves” are scale like sheets only one cell thick Roots are tiny rhizoids - a few epidermal cells that anchor the plant to the soil The sporophytes of bryophytes are not free living organisms The leafy green plant we think of as “moss” is the gametophyte generation The sporophyte generation grows out of the tissues of the gametophyte, and depends on its parent for nutrition Phylum Bryophyta – Mosses 16,000 species, from Greek bryon = moss - Mnium, Sphagnum Two growth types Cushiony moss - erect stalks Feathery moss - flattened mats, low-lying Moss plants are male or female (dioecious) “roof” Male plants have antheridia at the top Female plants have archegonia at the top Gametophytes are haploid, so can make gametes by mitosis Antheridia produce sperm Archegonia produce eggs Sperm swims through thin film of water from the antheridium to the archegonium Sperm drawn to the egg by chemical attractant Sperm swims down the neck of the archegonium Sperm fuses with egg, forms 2n zygote The male and female plant share a cigarette, discuss old times… Diploid zygote develops into the adult sporophyte, a small green stalk growing out of the top of the female plant Stalk can photosynthesize, but soon turns brown, lives off the parent plant (sound familiar??) Sporophyte consists of a stalk with a small capsule on the top Cells in capsule undergo meiosis, form haploid spores Capsule ripens, the lid or operculum opens up, releases the spores Spores germinate into tiny green threads called protonema (pl. = protonemata) Looks like tiny green algae….hmmmm… Buds on protonema develop into adult gametophytes Mosses can also reproduce asexually by fragmentation Mosses can also grow little vegetative buds called gemmae, that break off and grow into a new plant Mosses - Ecological Importance Pioneer species on bare soil Retains moisture and nutrients in ecosystems Seed bed for higher plants Most abundant plant in polar ecosystems Peat bogs cover 1% of the Earth’s land surface, area = half the United States !! Peat bogs are very acidic, pH = 4 or lower, most acidic natural environment cranberries and blueberries grow Mosses - Economic Importance Sphagnum moss is commercially important Compressed into peat, used for fuel Cotton absorbs 4-6 times its weight in water, but Sphagnum absorbs > 20 times its weight!! used for diapers enriching garden soil dressing wounds in war Phylum Hepaticophyta – Liverworts 9,000 species, Marchantia, Porella Simplest bodies of any green plant, looks like a flat scaly leaf with prominent lobes Lobes suggested the shape of a liver, hence hepato - phyta = Greek for “liver plant”, liver - wort fromAnglo Saxon wyrt = herb During the MiddleAges, because of its resemblance to the human liver, liverworts were used to treat liver diseases Doctrine of Signatures claimed that the creator has intentionally created plants to look like the parts of the body they could be used to cure! Mandrake root was a heal-all because it looked like an entire human body Can you guess what walnuts were used for? Walnuts were used to treat brain disease!! Liverworts store food as oil instead of starch, and lack stomata Some lack stomata, waxy cuticle – true of other bryophytes also, have both or neither Transitional group – sporophytes are more terrestrial stage, gametophytes more aquatic Life cycle similar to mosses - gametophyte is dominant stage (the leafy green plant) Archegonia hang from the underside of tiny umbrellas Sperm swims to the egg, zygote develops into tiny diploid sporophyte that remains attached to the umbrella Haploid spores are surrounded by elaters, long, twisted, moist cells When the elaters dry out, they twist and jerk around, scatter the spores Asexual reproduction by gemmae cups, little cups with tiny liverwort inside, dispersed by drop of water PhylumAnthocerophyta – Hornworts 100 species - Anthoceros Gametophytes look like liverworts, but send up a tiny moss-like sporophyte More closely related to mosses (stomata) Symbiotic with cyanobacteria Nostoc and Anabaena, which fix nitrogen for the hornwort Ferns and FernAllies taxonomy part among the three types? Tracheophytes (vascular plants) completed the conquest of the Earth begun by the primitive bryophytes The evolution of the spore was the key to the bryophytes emergence onto land The evolution of vascular tissue and seeds let tracheophytes become fully terrestrial Over 279,000 species of tracheophytes (most of them flowering plants!) Big split in plant evolution during the Early Devonian Lycophytes - club moss etc. Euphyllophytes - plants with true leaves By the mid Devonian, euphyllophytes had split again into Monilophytes - ferns and fern allies Lignophytes - seed plants True leaves (euphylls) formed as a web of tissue stretched between small terminal branches Evolution of true leaves (euphylls) was a response to global environmental change Big global drop in carbon dioxide when vascular plants evolved and spread CO i2 a trace gas (!), much was taken up by early plants to make glucose through photosynthesis True leaves were an evolutionary response to this global drop in CO 2 Thin flat blades of tissue were a more efficient way to capture an essential gas that was present in very low concentration Lycophyta, Sphenophyta, and Psilophyta are often lumped together as “fern allies” Ferns and fern allies are vascular plants that reproduce by means of spores rather than seeds Ferns and fern allies are the most primitive living tracheophytes Tracheophytes have highly specialized roots, stems, and leaves Gametophytes and sporophytes usually have a symbiotic fungi (mycorrhizae) Many similarities to bryophytes Ferns and allies have free-swimming flagellated sperm, larger non-motile egg Sperm must swim through water, so ferns and allies are limited to moist environment Sporophyte develops directly from the gametophyte, no protection from desiccation Differences between bryophytes and ferns Sporophyte is the dominant stage in ferns (instead of gametophyte) Ferns and fern allies are monoecious - antheridia and archegonia on same plant Gametophytes are free-living plants, very small, only develop in moist areas Differences between bryophytes and ferns Sporangia attached to sporophylls Sporophylls organized into club-shaped strobili Spread by rhizomes, modified underground stems that help spread it around Before ferns evolved, bryophytes were the dominant plants on Earth Tracheophytes quickly became the dominant flora More highly evolved root-shoot system Efficient vascular tissues Larger size Ferns and fern allies formed planetary forest cover by the end of the Paleozoic, with trees 20-100 feet tall! Seed plants (primitive gymnosperms) evolved in the late Paleozoic, rapidly became the dominant plants Only ferns managed to compete with seed plants, and are still a significant group today Today most ferns and fern allies are small, inconspicuous plants FernsAllies - Economic Importance Most of our modern coal deposits were formed by horsetails, club mosses, and other trees during the Carboniferous (end of the Paleozoic) Phylum Lycophyta - club moss Phylum Sphenophyta - horsetails Phylum Psilophyta - whisk ferns Phylum Pterophyta – ferns importance question coal - ferns and fern allies any groups can go into that coal
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