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Lecture 15

BIO SCI 94 Lecture 15: Green Algae and Land Protist Part 2Premium


Department
Biological Sciences
Course Code
BIO SCI 94
Professor
Brad Hughes
Lecture
15

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2/8/19
Silurian-Devonian Explosion
Rocks 416-359 mya, fossils found from major plant lineages
All adaptations for plants to live on land include:
Water conducting vascular tissue
Roots
Stomata
Leaves
Plants colonize land alongside fungi
The Carboniferous Period
Coal deposits found in sediments 359-299 mya
Coal-carbon rich rock with fossil spores, branches, leaves and tree trunks
Fossils from seedless vascular plants
Coal formation needs water
Carboniferous fossils reveal forest swamp present
Diversification of Gymnosperms
Gymnosperms-abundant 299-145 mya
Present day 5 major groups of gymnosperms:
ginkgophyta(ginkgoes)
Cycadophyta (cycads)
cupressophyta(redwood, junipers, yews)
pinophyta(pines, spruces, firs)
ginetophyta(gnetophytes)
Gymnosperms thrive in dry habitats
Wet and dry environments filled with green plants
Diversification of Angiosperms
Flowering plants appear 150 mya, continue to diversify today
First flowering plants ancestor of grass, orchid, daisies, oaks, maples, roses
Summary of the Land Plant Fossil Record
Green algae first, next vascular plants, seedless vascular plants, and seed plants
Late fossil record organisms less dependent on moist habitats
Support idea that:
Green plants evolved from green algae
Land plants evolve for dry habitats
Themes in the Diversification of Land Plants
Land plant evolution needed adaptations for photosynthetic organisms to move
from water to land
How Did Plants Adapt to Dry Conditions?
Plants adapt to where only part of tissue wet
Tissue meet air→ dry out and die

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Natural selection prefer plants that resist drying problem
Green plants survive on land→ light, carbon dioxide more abundant
Adaptation of water problem
Prevent water loss from cells
Provide protection from UV radiation
Move water throughout tissues
Preventing Water Loss: Cuticle and Stomata
Cuticle- watertight sealant
Covers part of plant aboveground
Allows plant to survive in dry habitats
Cuticle blocks carbon dioxide
Stoma
Includes opening(pore) and guard cells
Guard cell change shape→ pore opens or closes
Stomata in all land plants except liverworts which lack guard cells
Cuticle and stomata most important tools for plants to live on land
Providing Protection From UV Irradiation
Land plants exposed to more light→ faster photosynthesis
Exposed to UV rays
UV light damage DNA
Plants collect/make compounds to absorb UV light
Act as sunscreen→ protect plant DNA
The Importance of Upright Growth
First land plants grew low to ground
Must remain in contact with moist soil
High competition for space and light
Land plants that can grow tall → more sunlight
Harder to move water due to gravity
Weak to gravity and wind
Experimental Analysis:Vascular Tissue
Fossils in Rhynie Chert formation have plants that grow upright
Have elongated cells made into tissues along length of plants
Cells believed to be part of water conducting tissue because fossilized cells had
Cellulose containing cells similar to water conducting cells in today's
mosses
Cell walls with thickened rings with lignin
Lignin-strong polymer
The Origin of Vascular Tissue
Evolutionary sequence in water conducting cell
Lignin in cell walls of water conducting cells- defining feature of vascular tissue
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Evolution of vascular tissue allowed parts to:
Support erect stems
Transport water from root to tissues above ground
Vessel Elements
In vascular tissue, vessel elements line up to form pipelike structure
Tracheids or combo of tracheids and vessels form wood
Wood-strong support material
Mapping Evolutionary Changes on the Phylogenetic Tree
Cuticle, stomata, vascular allow plants to live on land
Adaptations to live on land evolved just once
Convergent evolution occur-vessels evolved in gnetophytes and angiosperms
How Do Plants Reproduce in Dry Conditions?
Life cycle of eukaryotes have several functions:
Increase genetic variability
Increase number of individuals
Disperse individuals to new habitats
Green plants overcome obstacles from living in water to land:
Spores have tough coat of sporopollenin to resist drying
Gametes made in multicellular structures
Embryos cared for by parent plant
Producing Gametes in Protected Structures
Early land plants have gametangia- protect gametes from drying and damage
All plant except angiosperms have them
Individuals produce male and female gametangia
Antheridium-sperm producing structure
Similar animal testes
Archegonium-egg producing structure
Animal ovaries
Land Plant Embryos Are Nourished by Their Parent
Unlike ancestors, land plants keep eggs
Eggs form inside archegonia
Unlike green algae, land plant zygotes
Develop on parent plant
Form multicellular embryos-taken cared by parent plant
Retention of embryo important in land plant evolution
Group’s name Embryophyta
Retention of fertilized egg in embryophytes=pregnancy in mammals
Alternation of Generations
Land plants go through alternation of generations- individuals have
Multicellular haploid phase-gametophyte
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