packet #68 chapter #29. introduction there are more than 290,000 species of plants that inhabit the...
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Packet #68Chapter #29
IntroductionThere are more than
290,000 species of plants that inhabit the earth.
How, and why, based on the theory of evolution, did plants venture out of the sea and onto dry land?Some answers lay with
the charophyceans Green algae
Information About PlantsPlants are multicellular, eukaryotic
photoautotrophs.The cells, that make up plants, have cell walls
that are composed of cellulose.The pigment chlorophyll may be found in two
forms a & b
“Evolutionist Thoughts”
Diversion of Algae and Land PlantsEmbryophytes
(plants with embryos) is the traditional scheme and is mostly associated with Kingdom Plante.
It is thought that plants evolved from green algae.Charophyceans
Morphological & Biochemical EvidenceBelow are four traits that “suggest” an evolutionary
relationship between charophyceans and land plants Homologous peroxisomes
Both groups contain enzymes that minimize the loss of organic products due to photorespiration
Formation of phragomoplast Synthesis of cell plates during cell division involves the formation of
phragomoplast Homologous Sperm
Many plants (gymnosperms) have flagellated sperm that match charophycean sperm
Homologous cellulose cell walls Cell walls of both land plants and charophyceans contain 20-26%
cellulose
Genetic EvidenceAdditionally, there are key nuclear genes,
which result in the production RNA, that are used to help make cytoskeleton proteins.
Homologous chloroplastsAlgal plastids, of green algae and algal groups
such as euglenoids, are similar to those found in land plants
Chloroplast DNA found in charophyceans, green algae, is most closely related to that found in land plants.
Adaptations Enabling the Move to LandCharophyceans have
a layer of a durable polymer called sporopollenin.Prevents exposed
zygotes from drying out.
May be the precursor to the tough sporopollenin walls that encase plant spores.
Adaptations IIThe colonization of land by plants required
the evolution of many anatomical, physiological and reproductive adaptations
Adaptations IIIWaxy Cuticle
Used to protect against water lossPrevents desiccation (drying up) of plant
tissuesStomata
Allows gas exchange needed for photosynthesisMulticellular gametangia have (sterile)
nonreproductive cells as well as gametesThe fertilized egg develops into a multicellular
embryo within the female gametangium.
AdaptationsPlant life cycle alternates between haploid
and diploid generations (alternation of generation)
AdaptationsPlant Life CycleThe haploid portion is
the gametophyte generationProduces haploid
gametes via mitosis Within antheridia
Male parts Within archegonia
Female parts
Gametes fuse to form the diploid zygote of the sporophyte generation
AdaptationsPlant Life CycleThe diploid portion is
the sporophyte generationZygote develops
within the archegonium
Zygote produces haploid spores via meiosis
Spores divide via mitosis and develop into the gametophyte generation
AdaptationsPlant Life Cycle (Extras)All plants produce spores via meiosis ONLY
as opposed to algae and fungi which produce spores via meiosis or mitosis
In “lower plants,” the gametophyte generation is the dominant stage
In “higher plants,” the sporophyte generation is the dominant stage
Adaptations VIProduction of Secondary Compounds
Plants produce many unique compounds, such as terpenes, alkaloids and tannins, as byproducts of primary metabolic pathways.
The compounds, byproducts, may have bitter tastes, strong odors or toxic effects and help plant defend itself against herbivores.
Later AdaptationsMosses and ferns, although adapted to life on
land, have motile sperm cells that require water as a transport medium for fertilization.
Ferns, and vascular plants, that “evolved” at a later time, have xylem, to conduct water, and phloem, to conduct dissolved sugar.