Plant Tutorial 1 PDF

Plant Diversity (non-flowering plants) Learning objectives: - Understand the key evolutionary adaptations that allowed plants to survive and reproduce on land - Compare the life cycles and unique features of non-flowering plants (bryophytes, seedless...

Plant Diversity (non-flowering plants) Learning objectives: - Understand the key evolutionary adaptations that allowed plants to survive and reproduce on land - Compare the life cycles and unique features of non-flowering plants (bryophytes, seedless vascular plants, and gymnosperms) General Characteristics of Land plants: - Eukaryotic, Multicellular - Autotrophs - Cell wall (cellulose, sporopollenin) - Embryophytes (plants with protected embryos) - Terrestrial - Alternation of generations  Alteration of generations The gametophyte is haploid and produces haploid gametes by mitosis Fusion of gametes gives rise to the diploid sporophyte which produces haploid spores by meiosis All land plants undergo alternation of generations There is a trend toward reduction of the gametophyte generation in plant evolution  Land plants evolved from green algae Green algae called charophytes are the closest relatives of land plants Life in water vs life on land (advantage/disadvantage?) On land, plants needed: – Water transport mechanisms – Physical support – Mechanism to distribute gametes and progeny Adaptations of land plants develop in order to thrive on land: – Cuticle: waxy coating that retards water loss – Stomata: openings in stems and leaves; regulate gas exchange – Vascular tissues (xylem and phloem) – Embryos in a protective structure (seeds instead of spore) Figure 29.2 Zygenema, a charophyte  Ten phyla: plant evolutionary & diversity 9,000 species 13,000 species 225 species 1,200 species 12,000 species 1,025 species 290,000 species Define plants as embryophytes, plants with embryos Figure 29.7 Highlights of plant evolution  Nonvascular plants – Mosses, liverworts and hornworts; thought to be similar to earliest land plants – With no vascular transport system, they cannot grow very tall – Water transport is via diffusion – They have a thin cuticle or no cuticle, and most live in moist habitats – Nonvascular plants lack true leaves, stems, and roots but have analogous structures Mosses often cover the ground in dense mats  Nonvascular plants Mosses (Phylum Bryophyta) Liverworts (Phylum Hepatophyta) Hornworts (Phylum Anthocerophyta)  Liverworts - Gametophytes are larger and longer-living than sporophytes - Archegoniophore and antheridiophore are erect structures that contain the multicellular gametangia - Mature gametophytes produce flagellated sperm in antheridia an an egg in each archegonia Life cycle of a liverwort - Fertilization - Sperm must swim or be splashed by raindrops to an archegonium t fertilize an egg - Rhizoids anchor thallus to the substrate (Bryophytes do not have true roots) - Liverworts also reproduce asexually by fragmentation of the gametophyte Gemmae—clumps of cells in gemmae cups. Gemmae are dispersed by splashes of water in the cups (raindrops) - Hornwort and moss sporophytes have stomata for gas exchange; liverworts do not (air on the upper epidermis of thallus)  A closer look at the Marchantia (liverwort) sporophyte Sporophyte is small and depends on gametophyte for nutrition Foot absorbs nutrients from the gametophyte Cells of the seta/ stalk are very delicate and thin walled Sporophyte (2n) Elaters (blue threads)= cells which aid in the dispersal of spores (red dots) Sporangium/capsule  Mosses - Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium. Sperm swim through film of water to reach and fertilize egg - A sporophyte consists of a foot, seta (stalk), and sporangium (capsule), which discharges spores through a peristome Figure 29.8 The life cycle of a moss Gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time Peristome teeth respond to humidity, bending outward and opening the sporangium when the air is dry https://www.youtube.com/watch?v=jIJ9_EBoY-U  Hornworts Nonvascular plants The sporophyte has no stalk - The sporophyte has no stalk - Gametophytes are flat plates of From which part of this hornwort cells; sporophytes look like small would spores be released? horns - Hornwort cells have a single, large chloroplast  Nonvascular plants In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes; Sporophytes are typically present only part of the time and dependent on the gametophytes Require water for reproduction (limits bryophytes in the habitats in which they can live moist) Seedless vascular plants - Ferns and other seedless vascular plants were the first plants to grow tall - The ability to transport water and food throughout their bodies allowed them to spread to new environments and diversify rapidly - Seedless vascular plants have flagellated sperm and are usually restricted to moist environments Seedless vascular plants Two clades of seedless vascular plants: Phylum Lycophyta (club mosses, spike mosses, and quillworts) Phylum Monilophyta (ferns, horsetails, Microphylls whisk ferns) Megaphylls  Prothallium Gametophytes are tiny plants that grow on or below the soil surface Ferns (most nonvascular plants and seedless vascular plants) are homosporous In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation Figure 29.13 The life cycle of a fern - The most ancient vascular plants were - Heterosporous plants produce 2 spore homosporous—having one type of spore types: Megaspores develop into female - The spores produce one type of gametophytes—megagametophytes, gametophyte that has both female and which produce only eggs. male reproductive organs Microspores develop into male gametophytes—microgametophytes, which produce only sperm Fern sporophytes can be large and very long-lived Sporangia are borne on a stalk in Sorus (sori, plural) clusters called sori on the underside of the leaves New feature that evolved in seedless vascular plants: Sporophylls are modified leaves with sporangia - Sori are clusters of sporangia on the undersides of sporophylls - Strobili are cone-like structures formed from groups of sporophylls Fern leaflets with sorus Club moss with strobili  Seedless vascular plants All seedless vascular plants have conducting tissues with lignin (can grow bigger and upward). The gametophyte is physically independent of the sporophyte, but the sporophyte is the larger and longer-lived phase. Place the steps of the fern life cycle in order 1 Spores land on soil Through water, sperm swim from antheridium to archegonium Prothallus grows Sporophytes release spores Fertilization occurs Diploid zygote divides and give rise to a sporophyte Seed plants - Seeds and pollen grains are key adaptations for life on land -The Gymnosperms bear retention evolution of embryo “naked” seeds had typically on cones a downside: - The– In ferns and horsetails, reproductive sporophytes have to live in the adaptations same placeof as angiosperms their parent include flowers and fruits gametophyte and food throughout their Seed plants overcome this limitation bodies allowed them to – Embryos of seed plants are spread to new environments portable and can disperse to andnew diversify locationsrapidly Seed plants - Seeds and pollen grains are key adaptations for life on land Seeds provide some evolutionary advantages over spores: 1. remain dormant until conditions are favorable for germination 2. Seeds have a supply of stored food 3. They may be transported long distances Seed Plants have reduced gametophyte (usually microscopic), dependent on surrounding sporophyte tissue for nutrition and dominant sporophyte Figure 30.2 Gametophyte-sporophyte relationships in different plant groups  Gymnosperm diversity The gymnosperms consist of four phyla – Cycadophyta (cycads) – Gingkophyta (one living species: Ginkgo biloba) – Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) – Coniferophyta (conifers, such as pine, fir, and redwood) Today, cone-bearing gymnosperms called conifers dominate in northern latitudes  Phylum Cycadophyta These thrived during Mesozoic, but relatively few species exist today Unlike most seed plants, cycads have flagellated sperm Individuals have large cones and palmlike leaves Figure 30.7a Exploring Gymnosperm Diversity Cycad roots harbor symbiotic nitrogen-fixing cyanobacteria Cycads are popular landscaping plants.  Phylum Ginkgophyta Figure 30.7b Exploring Gymnosperm Diversity Consists of a single living species, Ginkgo biloba Like cycads, has flagellated sperm It has a high tolerance to air pollution and is a popular ornamental tree Grow as vines, trees, or shrubs  Phylum Gnetophyta This phylum comprises three genera: Gnetum, Ephedra and Welwitschia Species vary in appearance, and some are tropical whereas others live in deserts Grow as vines, trees, or shrubs; have vessel elements in addition to tracheids  Phylum Coniferophyta This phylum is by far the largest of the gymnosperm phyla Most conifers are evergreens and can carry out photosynthesis year round Needle-like leaves have small surface area They dominate high-latitude and high-altitude forests  Gymnosperms bear “naked” seeds, typically on cones The seeds are exposed on sporophylls that form cones Most gymnosperms are cone-bearing plants called conifers Three key features of the gymnosperm life cycle are – Dominance of the sporophyte generation – Development of seeds from fertilized ovules – The transfer of sperm to ovules by pollen The Life Cycle of a Pine The pine tree is the sporophyte and produces sporangia in male and female cones Small cones produce microspores called pollen grains, each one contains a male gametophyte The familiar larger cones Pollen containeliminates ovules, need whichfor a produce film megaspores of water and can bethat develop into dispersed greatfemale distances by gametophytes air or animals It takes nearly three years from cone production to mature seed  Staminate cone Staminate cones (male cones) Microsporophylls are modified needles. Contained within each is a sporangium containing microsporocytes (2n). Each one will under meiosis to produce 4 haploid spores. Each spore will develop into a pollen grain. Ovulate cones (female cones) Ovule Megasporophyll  From ovule to seed in a gymnosperm - A seed develops from the whole ovule Figure 30.3 From ovule to seed in a gymnosperm - A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat  Seed plants (gymnosperms) Seed plants are defined by the presence of seeds and pollen grains. Seed plants do not require liquid water for fertilization. All seed plants are heterosporous, and their gametophytes are much smaller (and dependent on) than their sporophytes. Key concepts: Plants evolved from green algae Mosses and other nonvascular plants have life cycles dominated by gametophytes Ferns and other seedless vascular plants were the first plants to grow tall Seeds and pollen grains are key adaptations for life on land Gymnosperms bear “naked” seeds typically on cones Vocabulary update Microphylls, leaves with a single vein Megaphylls, leaves with a highly branched vascular system Sporophylls are modified leaves with sporangia Sori are clusters of sporangia on the undersides of sporophylls Strobili are cone-like structures formed from groups of sporophylls