Transcript seed plants
1 SEED PLANTS Gymnosperms & Angiosperms 2 Differences between seed-plants and lower plants The gametes of seed plants do not depend on water for fertilisation Spores of seed plants are heterosporous Microspores are male spores Megaspores are female 3 Common features of seed plants and pteridophytes Both have roots, stems and leaves Both have vascular tissue Evolution Of Land Plants 4 REMEMBER: Terrestrial plants evolved from a green algal ancestor The earliest land plants were nonvascular, spore producers (bryophytes) Ferns were the 1st vascular, spore producing plants Gymnosperms & angiosperms were the 1st vascular, seed plants 5 copyright cmassengale Characteristics of Seed Plants 6 Multicellular Autotrophic Alternation of Generations Reproduce by Seeds Vascular tissue for transport Heterosporous – make female megaspores & male microspores Dandelion dispersing seeds Reasons for Success on Land 7 Waxy cuticle Stomata with guard cells to open & close Gametes protected in tissue called Gametangia Pollen tube to transfer sperm to the egg instead of water Seeds protect developing embryo & contain food 8 Major evolutionary advancements of seed plants Pollen grains Resistant seeds copyright cmassengale Major evolutionary advancements of seed plants 9 Pollen grains Produced from microspores Contain the male gametes (sperm cells) Transported by wind, water and animals to the female part of a flower Pollen grain grows a pollen tube Male gametes move through the pollen tube to the female egg Water is not needed for sperm to swim in 10 11 Major evolutionary advancements of seed plants Resistant seeds copyright cmassengale SEEDS 12 Allows a plant embryo to lie dormant Until conditions become suitable for germination Dormant = no metabolic reactions can take as no water is present in the seed Seeds 13 Seeds contain a young, developing plant embryo Seeds are covered with a protective seed coat (testa) Inside is stored food or endosperm that the young plant uses as it begins to sprout or germinate Seeds form from ripened ovules after fertilization copyright cmassengale Parts of a Seed Embryo 14 Primary root or Radicle One or two embryonic leaves called Cotyledons Plumule becomes the shoot Stem like portion below cotyledons called Hypocotyl Stem like portion above cotyledons called Epicotyl copyright cmassengale 15 Endosperm (3n) Seed Coat Cotyledon Plumule Epicotyl Hypocotyl Radicle 16 Seed Dispersal 17 Seeds must be scattered (dispersed) away from the parent plant Testa (seed coats) may last thousands of years Seeds eaten by animals aren’t digested but pass out with wastes Seed Dispersal 18 Seeds may have adaptations such as stickers, hooks, or fuzz to adhere to animals copyright cmassengale Seed Dispersal 19 Both water and wind can scatter seeds Wind Dispersal Water Dispersal copyright cmassengale Seed Dispersal Methods 20 copyright cmassengale 21 copyright cmassengale Seed Germination 22 Early growth of plant embryo Begins when seed absorbs water & breaks seed coat (testa) Embryo uses stored food of cotyledons to begin growing copyright cmassengale Importance of seed development 23 Enabled seed plants to colonise the whole earth Seeds could survive unfavourable conditions Spores of ferns and mosses were not able to do so GYMNOSPERMS 24 Introduction – Gymnosperm means “naked seed” (From the Greek: gymnos = naked; sperm = seed) More advanced than ferns – do not have spores, they have seeds. The seeds of the gymnosperms lack a protective enclosure (unlike flowering plants which have flowers and fruit). Examples of gymnosperms: Conifers (pine trees), cycads, ginkgo biloba Gymnosperms 25 Mainly woody plants that include Oldest living trees: bristlecone pine, 5 000 yrs old! Most massive trees (giant sequoia): up to 375 ft. tall, 41 ft wide! Tallest living trees (redwoods) Conifers 26 Conifers adapted to temperate to cold regions Narrow leaves (needles) help to conserve water Covered by resins – for protection from predators, fire, etc. copyright cmassengale Other gymnosperms 27 Cycads – short shrubs, native to tropical regions (look like palms) Ginkgo biloba – a “living fossil”, male and female tree, used as a medicinal plant copyright cmassengale Other gymnosperms 28 Welwitschia – a bizarre gymnosperm plant that grows in Namib desert (So. Africa). Live up to 2000 years in these extreme conditions! Only makes two leaves throughout its life. It takes water from sea mist Characteristics of gymnosperms 29 Mostly trees with needle-like leaves copyright cmassengale Characteristics of gymnosperms 30 Have true leaves and roots with vascular tissue copyright cmassengale Characteristics of gymnosperms 31 Have sporangia in cones copyright cmassengale Characteristics of gymnosperms 32 Are heterosporous copyright cmassengale Characteristics of gymnosperms 33 Pollen grains produce a pollen tube Characteristics of gymnosperms 34 Gymnosperms produce seeds which are naked on the sporophylls of the female cone 35 copyright cmassengale Characteristics of gymnosperms 36 Embryo is protected inside a seed Gymnosperm life cycle 37 Exhibits alternation of generations Sporophyte generation (2n) is dominant Gametophyte generation (1n) is contained in and dependent on the sporophyte generation LIFE CYCLE GYMNOSPERM copyright cmassengale 38 39 40 SIGNIFICANCE OF GYMNOSPERMS 41 Ecological importance: Extra stuff Provide food and habitat for wildlife Forests prevent soil erosion Reduce greenhouse-effect gasses Economic and commercial importance: Lumber for wood, paper, etc. Resins – wood, furniture, etc. Ornamental plants (trees, landscaping) Food – pine nuts (pesto, etc.) 42 ANGIOSPERMS 43 Angiosperm means “covered seed” Have flowers Have fruits with seeds Live everywhere – dominant plants in the world 235,000 species (80% of Plant Kingdom) Angiosperms are the most successful and advanced plants on earth EVOLUTION OF ANGIOSPERMS 44 Advancements over gymnosperms: Angiosperms have flowers – many use pollinators Fruits and seeds – adapted for dispersal Double fertilization of the endosperm in the seed copyright cmassengale CHARACTERISTICS OF ANGIOSPERMS 45 Also have true leaves and roots Have vascular tissue (xylem has tracheids and vessel elementsgymnosperms only have tracheids) Flowers Fruit, with seeds enclosed in an ovary FLOWERS AND FRUIT 46 Both flowers and fruit are used in a variety of ways to help with reproduction ANGIOSPERM LIFE CYCLE 47 48 DECREASING DEPENENCE ON WATER FOR REPRODUCTION 49 Land plants evolved from aquatic species In water, gametes swim to reach each other Mosses and ferns retain their motile gametes As a result they have to live in moist areas Ferns developed a waterproof cuticle and vascular tissue to make them less dependent on water but they still need it for reproduction copyright cmassengale DECREASING DEPENENCE ON WATER FOR REPRODUCTION 50 Seed bearing plants (gymnosperms and angiosperms) lost their dependence on water for fertilisation And as a result could reproduce in dry climates These plants developed: The pollen grain Protected female gamete Embryo which does not need to germinate immediately (protected inside the seed) THE POLLEN GRAIN 51 Contains the non-motile male gamete Protected against drying out by the outer wall Carried to the female over long distances by wind or animals PROTECTED FEMALE GAMETE 52 The female gamete (egg cell) is deep inside the ovule Gives it protection against drying out The pollen grain develops a pollen tube through which the male gamete can reach the female gamete SEED 53 Protects the embryo against drying out Does not have to germinate immediately Only when water is available (not dependent on water) Contains food for the embryo PHYLOGENICS 54 Is a branch of learning that tries to show the evolutionary relationships among organisms PHYLOGENIC TREE 55 Also called a cladogram Represents the evolutionary relationships among a set of organisms that arose from a common ancestor Do not contain information about time NOTE THE FOLLOWING WHEN LOOKING AT A PHYLOGENIC TREE 56 Ancestral organism Nodes on the tree Distance between groups Relationship between groups Historical structural changes Clades THE ANCESTRAL ORGANISM 57 Is on the trunk of the tree copyright cmassengale THE NODES 58 Where branches meet Show where species have diverged They represent the common shared ancestor of all taxa beyond the node TAXON = GROUP OF RELATED ORGANISMS 59 THE DISTANCE BETWEEN GROUPS Indicates the degree of relationship copyright cmassengale MAJOR STRUCTURAL CHANGES IN HISTORY 60 E.g. the development of vascular tissue/seeds in plants 61 Evolutionary tree of dog breeds and gray wolves CLADE 62 Is a group in a phylogenic tree which begins with a node (ancestor) and includes all the descendents of the ancestor 63 copyright cmassengale 64 Phylogenetic tree of Theropods Theropoda dinosaurs, and a clade consisting of modern birds). 65 66 Phylogenetic tree of vertebrates 67 Flower structure 68 Male sex organs: Stamens, composed of anther – organ that produces pollen (male gametophyte) Female sex organs: The carpel Ovary is the enlarged basal portion of carpel that contains the ovules (female gametophyte) The stigma is the receptive portion of the carpel for pollen grains to adhere copyright cmassengale Flower structure 69 Non-reproductive parts: Sepals (green) are the outermost whorl of leaf-like bracts Petals (usually colored) are the inner whorl of leaf-like bracts Both can have various shapes and colors Tepals -_______________ copyright cmassengale Angiosperm life cycle 70 Heterosporous: forms two different types of spores (micro- and megaspores; male and female spores) Male – pollen grains contain tube nucleus and generative cell (2 sperm nuclei) Female – female gametophyte contains egg and 2 polar nuclei copyright cmassengale Angiosperm lifecycle 71 Flowering plants exhibit alternation of generations. The large, familiar flowering plant is the diploid sporophyte, while the haploid gametophyte stages are microscopic. The unique feature about the life cycle of flowering plants is a double fertilization that produces a diploid zygote and a triploid endosperm or nutritive tissue. copyright cmassengale Double fertilization 72 Pollen grain germinates on stigma forming a pollen tube, which grows down style to the ovary Pollen has 2 haploid sperm nuclei, which travel to the ovary One sperm nucleus fertilizes the haploid egg forming the 2n zygote Another sperm nucleus unites with the 2 polar nuclei, forming the triploid (3n) endosperm copyright cmassengale Seeds 73 Fertilized egg grows into a ___________, which grows into plant embryo Endosperm is stored food tissue – for the embryo to grow Mature ovule becomes the seed coat and/or fruit copyright cmassengale