BIOL 005B Lecture Notes - Lecture 20: Charophyta, Sporopollenin, Non-Vascular Plant
BIOL 005B Lecture 20: Plant Diversity and Seedless Plants
●Overview: The Greening of Earth
○For more than the first 3 billion years of Earth’s history, the terrestrial surface was
lifeless
○Since colonizing land, plants have diversified into roughly 290,000 living species
○Plants supply oxygen and are the ultimate source of most food eaten by land
animals
○The advent of plants on earth cannot be understated
■They helped make the atmosphere we now energy (and require) possible
■They are the bottom (base) of most food webs on the planet (capture solar
energy and convert it to a form that is usable by other life forms)
●Land plants evolved from green algae
○Plants evolved from protists generally, but more specifically from green algae
(Charophyceans or Charophytes)
○Adaptations Enabling the Move to Land
■Charophyte ancestors lived at the water’s edge where they had access to
high light availability, nutrient rich soil and fewer herbivores and
pathogens
■But
, land presented challenges: a scarcity of water and lack of structural
support
■In charophytes (and their ancestors) a layer of a durable polymer called
sporopollenin prevents exposed zygotes from drying out
■This adaptation allowed them to take advantage of an open “niche” in
habitats and move onto land
●We will concentrate on the divergence between the Charophyceans and Land Plants
○Movement onto land represents a major change in the Earth’s surface
○It also represents an explosion in available habitats and niches for other
evolutionary divergences
○The evolution of these plants moves towards less dependence on free water and a
seed stage that is more packaged in a protective coat
○Common Features Between Charophytes and Land Plants
■Multicellular
■Eukaryotic
■Photosynthetic
■Autotrophic
■Cell walls of cellulose (and other materials)
■Many biochemical details
○Derived Traits of Plants
■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
●Alternation of Generations
○How Alternation of Generations work:
■Two different free-living stages per generation
●Produces gametes (2n)
●Haploid stage where fertilization occurs
●Walled Spores Produced in Sporangia
○The sporophyte produces walled spores (haploid) in organs called sporangia
○Spore walls contain sporopollenin, which makes them resistant to harsh
environments
●Multicellular Gametangia
○Gametes are produced within organs called gametangia
○Female gametangia, called archegonia, produce eggs and are the site of
fertilization
Document Summary
Biol 005b lecture 20: plant diversity and seedless plants. For more than the first 3 billion years of earth"s history, the terrestrial surface was lifeless. Since colonizing land, plants have diversified into roughly 290,000 living species. Plants supply oxygen and are the ultimate source of most food eaten by land animals. The advent of plants on earth cannot be understated. They helped make the atmosphere we now energy (and require) possible. They are the bottom (base) of most food webs on the planet (capture solar energy and convert it to a form that is usable by other life forms) Plants evolved from protists generally, but more specifically from green algae ( charophyceans or charophytes ) Charophyte ancestors lived at the water"s edge where they had access to high light availability, nutrient rich soil and fewer herbivores and pathogens. But , land presented challenges: a scarcity of water and lack of structural support.
