Land Plants - Mosses and Worts PDF

Land Plants Mosses and Worts  Green Algae Cyanobacteria First Ferns First Seed Plants Land Plants The age of the earth is 4.6 Billion Years  Phylogeny of Plants...

Land Plants Mosses and Worts  Green Algae Cyanobacteria First Ferns First Seed Plants Land Plants The age of the earth is 4.6 Billion Years  Phylogeny of Plants 3 Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.  Chara species, a pond organism 5 mm Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) 40 µm  Storming the Beaches In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens Land presented challenges: a scarcity of water and lack of structural support  Seed plants, about 305 mya Vascular plants, about 420 mya Origin of land plants, about 475 mya 6 Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.  Four key traits appear in nearly all land plants but are absent in the charophytes: – Alternation of generations (with multicellular, dependent embryos) – Walled spores produced in sporangia – Multicellular gametangia – Apical meristems – Linear growth from root and shoot tips Other traits that many plants have include – Cuticle Provides protection and controls moisture loss – Secondary compounds Defense against herbivory and UV protection  Nonvascular plants – Bryophytes – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta Vascular plants – Seedless – Seeds  Important points about Alteration of Generations The gametophyte is haploid and produces haploid gametes by mitosis Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis The diploid embryo is retained within the tissue of the female gametophyte Nutrients are transferred from parent to embryo through placental transfer cells Land plants are called embryophytes because of the dependency of the embryo on the parent  Haplodiplontic Life Cycle Multicellular diploid stage – sporophyte – Produces haploid spores by meiosis – Diploid spore mother cells (sporocytes) undergo meiosis in sporangia Produce 4 haploid spores First cells of gametophyte generation Multicellular haploid stage – gametophyte – Spores divide by mitosis – Produces gametes by mitosis – Gametes fuse to form diploid zygote First cell of next sporophyte generation  11 Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.  Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte Sporophytes and sporangia of Sphagnum (a moss)  Multicellular Gametangia Gametes are produced within organs called gametangia Female gametangia, called archegonia, produce eggs and are the site of fertilization Male gametangia, called antheridia, are the site of sperm production and release  Archegonium Female gametophyte with egg Antheridium with sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort)  Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome Hornwort and moss sporophytes have stomata for ule gas exchange Seta Life cycle of Mosses  Hornworts Earliest fossils are in Cretaceous, so origin is a mystery About 100 known species An Anthoceros hornwort species Sporophyte Gametophyte  Ecology of Mosses Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum is an important global reservoir of organic carbon Peat bogs make up an estimated 70 years of industrial carbon – Peat bogs are releasing carbon at an increasing rate  Peat is rich in carbon Beginning source of coal deposits More than 20% of homes in Ireland use peat bricks to heat the house Peat is composed of many plants but sphagnum moss is common in peat bogs 2% of global landmass is peat – 8 billion terajoules of energy stored in the peat bogs