Chapter 29 Plant Diversity I: How Plants Colonized Land

 For more than 3 billion years, earth was lifeless  Only within the last 500 years that small plants, fungi, and animals joined plants ashore  Plant roots created habitats for other organisms by stabilizing landscapes. Plants provide oxygen and most of the food eaten by terrestrial animals

Plants and algae are very similar  Multi-cellular, eukaryotic, photosynthetic autotrophs  Cell wallsAlgae  Dinoflagellates  Chloroplasts Plant

Morphological and Molecular Evidence  Four distinct traits help explain this:  Rosette-shaped cellulose-synthesizing complexes  Peroxisome enzymes  Structure of flagellated sperm  Formation of a phragmoplast

Rosette-shaped cellulose- synthesizing complexes and Peroxisome enzmes  RSCSC: Circular, pedal shaped array of proteins in the plasma membrane. Synthesize the cellulose microfibrils of the cell wall  Peroxisome enzymes: help minimize the loss of organic products as a result of photorespiration

Structure of flagellated sperm and Formation of a Phragmoplast  Flagellated Sperm: The structure of the sperm resembles the sperm of charophytes. Male reproductive cell  Formation of a phragmoplast: Forms during cytokinesis. Forms “scaffolding” during the formation of two daughter cells

Adaptations Enabling the Move to Land  Charophytes have a thin layer of a polymer called sporopollenin which prevents drying out  Sun was unfiltered by water and plankton, the atmosphere offered more carbon dioxide, the soil was rich in nutrients and minerals

Derived Traits of Plants  These traits emerged after land plants diverged from their algal relatives when they came ashore  The four traits are:  Alternation of Generation  Walled Spores Produced in Sporangia  Multi-cellular gametangia  Apical Meristems

Alternation of Generations  All plants show alternation of generations in which two multi-cellular body forms alternate  Gametophyte: uses mitosis  Sporophyte: uses meiosis, makes spores

Walled Spores Produced in Sporangia  Sporangia: multi-cellular organs that are found on the sporophyte and produce spores  Within sporangia, diploid cells called sporocytes undergo meiosis and generate haploid spores  Outer tissues of sporangia protect spores until they are released into the air

Multi-cellular gametangia  Plant gametophytes produce gametes within organs called gametangia  Female gametangia are called archegonia, produces an egg  Male gametangia are called antheridia, produces a sperm  Each egg is fertilized in an archegonium

Apical Meristems  They are localized regions of cell division at the tips of shoots and roots  Example: Plants need structures to get sunlight and CO2, and they need structures to get water and minerals  Cells produced by meristems differentiate into various tissues both internal and external

Other Derived Structures  Cuticle: a polyester and wax polymer coating that prevents plants from dehydrating  Mycorrhizae fungi help plants transfer water and nutrients more efficiently  Secondary compounds: alkaloids, terpenes, tannis, and phenolics such as flavonoids

The Origin and Diversification of Plants  Vascular system (cells joined into tubes that transport water and nutrients throughout the plant body)  Most plants have these complexes and are called vascular plants  Plants that do not have these extensive complexes are non-vascular plants (bryophyte) even though some mosses have some vascular tissue

 Vascular plants form a clade that comprises of 93% of all plant species. They can be categorized into smaller clades  Examples:  Lycophytes (club mosses and their relatives)  Pterophytes (ferns and their relatives)  Both these clades lack seeds, which is why they are called seedless vascular plants

 A third clade of vascular plants consists of seed plants, the vast majority of plant species today  Seed plants can be divided into two groups: gymnosperms and angiosperms. One has a protective seed coating, the other doesn’t

Liverworts  Shape thought to mean it treats liver disease  “ Thalloid” -flattened shape of their gametophytes  Gametophores look like miniature trees  “Leafy”- many leaf-like appendages  More Leafy than Thalloid

Hornworts  Sporophytes have long tapered shapes  lack a seta  Consist only of a sporangium  First species to colonize open moist soiled areas  Possible due to symbiotic relationship with cyanobacteria

Mosses  Familiar carpets of moss consist of mainly gametophytes  Blades of these “leaves” have one cell  More complex, multi-cellular “leaved” mosses exist  Sporophytes are elongated and visible  Young: green, photosynthetic  Mature: tan, ready to release spores

Bryophyte Gametophytes  Gametophytes larger and longer-living than sporophytes  Protonema -a mass of green, branched one-cell thick filaments  Produced when spores germinate  Large surface area enhances water absorption  One of more “buds” are produced

Bryophyte Gametophytes (cont.)  Each “bud” has a Gametophore  Gametophore- gamete producing structure on the bud  Form ground hugging carpets because:  Body parts too thin to support a tall plant  No Vascular Tissue=no long distance transportation of nutrients  Exception: mosses with conducting tissues in the center of their “stems”

Bryophyte Gametophytes (cont.)  Rhizoids -long, tubular single cells that anchor the gametophytes  Unlike roots:  not composed of tissues and  do not primarily transport water and minerals

Gametophytes and Reproduction  Gametangia -produce gametes  Multiple on each gametophyte  Archegonia- pear shaped unit where eggs are produced  Antheridium- unit where sperm are produced  Some gametophytes are bisexual, but most mosses have one

Bryophyte Sporophytes  Remain attached to their parental gametophytes for support  Smallest sporophytes of all plant groups  Foot- absorbs nutrients from the gametophyte  Seta(stalk)- conducts these materials to the sporangium  Capsule(sporangium)- uses materials to produce spores by meiosis

Bryophyte Sporophytes (cont.)  Peristome- a ring of interlocking, tooth-like structures in the upper part of the capsule  Teeth open under dry conditions and close when moist  Allows spores to be discharged gradually  Hornwort and Moss sporophytes are larger and more complex than liverwort

Stomata  Specialized pores that exchange CO2 and 02  Supports photosynthesis  Only hornwort and moss sporophytes have them  Main way water evaporates from the sporophyte  Stomata close, minimizing water loss when hot

29.3 Fern and other seedless vascular plants were the first plants to grow tall  During the first 100 million years of plant evolution, bryophytes or bryophyte-like plants were the prevalent vegetation.  Vascular plants dominate most landscapes today  Fossils show that lycophytes, ferns and other seedless vascular plants had well developed vascular systems by the Devonian period(416 Million years ago)  This set the stage for vascular plants to grow taller than their bryophyte counterparts.

Origins and Traits of Vascular Plants  Present-day vascular plants date back about 420 million years.  Had branched sporophytes that were not dependant on gametophytes for nutrition.  Grew no taller than 50 cm.  Lacked roots and other adaptations that evolved later.

Transport in Xylem and Phloem Xylem  Conducts most of the water and minerals.  Includes tracheids, which are tube shaped cells that carry water and minerals up from roots.  Water conducting cells are lignified. Their cell walls are strengthened by the polymer lignin. Phloem  Has cells arranged in tubes that distribute sugars, amino acids, and other organic material.

Evolution of Roots  Roots are organs that absorb water and nutrients from the soil.  Anchor vascular plants, allowing the shoot system to grow taller.  Root tissue of living plants resemble stem tissue of early vascular plants.

Evolution of Leaves  Serve as the primary photosynthetic organ of vascular plants.  Microphylls: Small, spine shaped leaves supported by a single strand of vascular tissue.  Megaphylls: Have highly branched vascular systems.  Microphylls first appeared 410 mya, while megaphylls didn’t emerge until about 370 mya.

Sporophylls and Spore Variations  Sporophylls: modified leaves that bear sporangia.  Produce clusters of sporangia called sori.  In many lycophytes, grouns of sporophylls form cone-like structures called strobili.  Most seedless vascular plant species are homosporous  They have one type of sporangium that produces one type of spore.  A heterosporous species has two types of sporangia and produces two kinds of spores: Megaspores (female gametophytes) and microspores (male gametophytes)

Phylum Lycophyta: Club mosses, Spike Mosses, and Quillworts  Present day species of lycophytes are relicts of Carboniferous period plants.  There were two types of lycophytes: small herbacious plants, and giant woody treelike plants.  Only the small lycophytes survived, representing about 1200 species.

Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives  By far the most widespread seedless vascular plants, more than sprecies.  More closely related to seed plants than to lycophytes.  Have features not found in lycophytes  Over-topping growth  Megaphyll leaves  Roots that can branch at various points

The Significance of Seedless Vascular Plants  Ancestors of these plants grew to great heights, forming the first forests.  Dramatically increased the removal of CO 2 from the atmosphere.  Caused global cooling that led to the widespread formation of glaciers.  Seedless vascular pants that formed the first forests eventually became coal.