Evolution of Plants PDF

Evolution of Land Plants  Land Plants The Greening of the Earth For more than 3 billion years of Earth’s history, the terrestrial surface was lifeless Life was in the seas Cyanobacteria likely existed on land ~1.2 billion years ago 475-500 million years ago, s...

Evolution of Land Plants  Land Plants The Greening of the Earth For more than 3 billion years of Earth’s history, the terrestrial surface was lifeless Life was in the seas Cyanobacteria likely existed on land ~1.2 billion years ago 475-500 million years ago, small plants, fungi, and animals emerged on land Land Plants  The Beginning of Land Plants The first plants were types of green algae and were aquatic This group included freshwater green algae, called charophytes Around 480 million years ago unicellular charophytes were evolving features that enabled them to survive out of water As a result, they had access to more sunlight and carbon dioxide and could photosynthesize more efficiently, producing more oxygen  The Beginning of Land Plants Charophytes are still around today  The Beginning of Land Plants From the fossil record we see that some ancient charophytes grew in wide flat mats in shallow water or on mud flats Tested by periods of drying and increased sunlight, provided a ground for natural selection to act upon  The Beginning of Land Plants From the fossil record we see that some ancient charophytes grew in wide flat mats in shallow water or on mud flats Tested by periods of drying and increased sunlight, provided a ground for natural selection to act upon The Beginning of Land Plants dryer Moisture wetter cooler hotter The Beginning of Land Plants dryer Moisture wetter cooler hotter  The Beginning of Land Plants Directional Selection! dryer Moisture wetter cooler hotter  The Beginning of Land Plants The first land plants were non-vascular and needed to grow directly on or near water No roots - not much organic soil – also no vascular tissues in their shoots  Moving from Water to Land Benefits: Unfiltered sunlight More carbon dioxide Few/no herbivores and pathogens Mineral substrates Challenges: Scarcity of water Solar radiation Lack of structural support against gravity  Water Challenges To avoid desiccation, plants evolved a cuticle; a waxy coating that is present on most exposed surfaces A form of waterproofing that also mediates solar radiation This limited the ability for the plant to conduct gas exchange, and thus they needed a means of opening & closing the waterproof seal Stoma and Guard Cells  Water Challenges To avoid desiccation, plants evolved a cuticle; a waxy coating that is present on most exposed surfaces A form of waterproofing that also mediates solar radiation This limited the ability for the plant to conduct gas exchange, and thus they needed a means of opening & closing the waterproof seal Stoma and Guard Cells  Water Challenges To avoid desiccation, plants evolved a cuticle; a waxy coating that is present on most exposed surfaces A form of waterproofing that also mediates solar radiation This also would limit the ability of the plant absorb water, and thus plants begin evolving roots that would be protected from the sun and could draw moisture from soil  Water Challenges Now water is only absorbed in one part of the plant – this is a new problem! A vascular system is then required to move water and minerals from areas where they are absorbed (the roots) to the rest of the plant Composes of the: Xylem that moves ______________ Phloem that moves _____________  Water Challenges Now water is only absorbed in one part of the plant – this is a new problem! A vascular system is then required to move water and minerals from areas where they are absorbed (the roots) to the rest of the plant Composes of the: Xylem that moves water & minerals Phloem that moves nutrients & water  Water Challenges Reproduction out of water is also a major barriers, for aquatic algae gametes can float to where they need to go – but out of water they are at risk of desiccation too They evolved sporopollenin, a durable polymer that covers exposed zygotes of charophytes and the walls of plant spores Analogous to amphibian eggs developing eggs shells as they transitioned to reptiles  Water Challenges The protection of gametes would continue with plants eventually evolving a wide range of structures to safeguard offspring, including: Pollen grains Seeds Cones Fruits  Gravity Challenges As plants became less dependent on remain close to water, both low to the ground and near waterbodies, they could expand in size Growing larger required increased structural integrity to offset gravity (remember in water they we buoyant) This was solved two ways: Turgor pressure More robust structure  Gravity Challenges Turgor Pressure Also called hydrostatic pressure, is the ability to regulate the pressure of fluid within cells Changes in osmolarity allow the flow of water into cells filling the vacuole Due to their tough cell wall (not seen in animals) the cell can become swollen and rigid This allows plant to either hold position or move body parts  Gravity Challenges Increased Structural Support Collenchyma and sclerenchyma are supporting tissues in land plants Collenchyma Sclerenchyma Collenchyma has thick cellulose cells walls Sclerenchyma has a thick cell wall of cellulose and a lignified secondary cell wall in mature cells (which do not contain cytoplasm and mostly filled with lignin) These are the really tough parts of plants like coarse fibers and wood  Gravity Challenges Which direction to go? Plants now need to know which way is up or down Auxins are group of plant hormones that control the growth of plants by modulating cell division Stems and roots respond differently to high concentrations of auxins: Cells in stems grow more Cells in roots grow less These hormones respond to different stimuli  Gravity Challenges Which direction to go? Phototropism causes an unequal concentration of auxins to cluster in the stem away from the light, causing that side to grow faster and thus bend toward the light Geotropism causes an unequal concentration of auxins to cluster on the underside of organs, in roots it slows growth (causing them to grow down), while in shoots they grow more (causing them to grow up)  Evolution of flowers and fruits Evolution of seeds, as well as collenchyma and sclerenchyma tissue Evolution of shoots, roots, proper leaves, xylem, and phloem Evolution of cuticle, stoma, rhizoids, and sporopollenin  Non-vascular Land Plants Early colonizers of land Modern examples are mosses, liverworts and hornworts Evolved the: Cuticle (to avoid desiccation), Stoma (to breath) Rhizoids (to hold to the substrate, and began the fungal partnership) Sporopollenin (to protect the gametes)  Non-vascular Land Plants Were the dominant (well only) land plant for 40 million years during the Ordovician period  Vascular Seedless Land Plants The beginning of being able to exploit the soil and enter drier habitats Modern examples are ferns and club mosses (lycopodium) Evolved the: Roots and shoots Proper leaves Vascular system  Vascular Seedless Land Plants The beginning of being able to exploit the soil and enter drier habitats Modern examples are ferns and club mosses (lycopodium) Evolved the: Roots and shoots Proper leaves Vascular system Vascular Seedless Land Plants Became the dominant land plant for the next 150-200 million years with humble begins…  Vascular Seedless Land Plants … becoming a major dense forest forming plant. With various species of tree fern covering the landscape Vascular Seedless Land Plants And there are still living tree ferns today!  Vascular Seeded Land Plants Evolved to live across a range of habitats and niches Divided into gymnosperms and angiosperms Evolved the: Seeds and means of seed dispersal Collenchyma and sclerenchyma tissue  Vascular Seeded Land Plants Gymnosperms Evolved in the Triassic and dominated for 150 million years All are perennial woody plants, include conifers, cycads, and ginkgo Name means 'naked seeds’, based on the unenclosed condition of their seeds Which contrasts with the seeds and ovules of angiosperms, which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones  Vascular Seeded Land Plants Angiosperms Evolved in the Cretaceous and have dominated since (65 million years) 300,000 named species Range from annual to perennial, and herbaceous to woody They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, the vast majority of broad-leaved trees, shrubs, vines, cacti, succulents, and most aquatic plants (i.e., non algae)  Vascular Seeded Land Plants Angiosperms Angiosperms are distinguished by: Flowers, the reproductive organs of flowering plants Endosperm within their seeds that forms after fertilization, but before the zygote divides, which provides food for the developing embryo (the cotyledon) Fruits, a closed carpel, that completely envelop the ovules (the seed)  Evolution of flowers and fruits Evolution of seeds, as well as collenchyma and Think about the family sclerenchyma tissue tree here, when things Evolution of shoots, roots, proper arose and image which leaves, xylem, and phloem plants you are familiar with are related to others Evolution of cuticle, stoma, rhizoids, and sporopollenin  Plants Paved the Way for Us Modulate global CO2 and O2 levels Including the expansion of an oxygen-rich atmosphere and stabilizing a cooler climate Vascular plants were able to colonise land away from water Significantly increased the bio-available chemical energy (the world runs on sugar) Produced organically enriched soils that allowed for more plants, and the formation of todays ecosystems Plants Paved the Way for Us  Plants Paved the Way for Us Modulate global CO2 and O2 levels Including the expansion of an oxygen-rich atmosphere and stabilizing a cooler climate Vascular plants were able to colonise land away from water Significantly increased the bio-available chemical energy (the world runs on sugar) Produced organically enriched soils that allowed for more plants, and the formation of todays ecosystems Plants Paved the Way for Us Our plants define our world  Plants Paved the Way for Us Modulate global CO2 and O2 levels Including the expansion of an oxygen-rich atmosphere and stabilizing a cooler climate Vascular plants were able to colonise land away from water Significantly increased the bio-available chemical energy (the world runs on sugar) Produced organically enriched soils that allowed for more plants, and the formation of todays ecosystems Read Chapter 29 and 30 of the textbook Pages 657-696 No seriously, do it. And take notes. This will help add deeper context to what we have discussed Reading it as we cover it provided you a much better knowledge base for midterms and exams compared to just studying close to the test