Chapter 26 - The Colonization of Land
Lichens
- symbiotic association of fungi and photosynthetic algae - can break down rock - important for soil formation - those minerals accessible to others
mycorrhizae
- symbiotic associations between plant roots and fungi - haustoria --- specialized hyphae to extract or exchange nutrients with plants - allows for easy transfer of nutrients between the two organisms - some parasitic but more are symbiotic - fungi more efficiently gather mineral ions using their mycelium than plant roots - plants share carbohydrates produced during photosynthesis
Alternation 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
Early Devonian
- there initial forests were large green plants, wood did not evolve/exist yet - giant fungi - in fossil evidence, near the water, first animals coming from water, and giant fungi structures
Chytrid Fungi
- unicellular and muticellular forms - globular multicellular fruiting body - lakes and soil - amphibian epidemic
bilateral symmetry
restrict gene flow and how the organism can enter the flower - may select the organisms which would work
stomata
specialized pores that allow the exchange of CO2 and O2 between the outside air and the plant
sporopollenin
- prevents exposed zygotes from drying out - found in plant spore walls - durable polymer
Fruit
The swollen ovaries of the plant that hold seeds - new generation of plants - protective coating = nutrients for the seeds - co-evolved to attract animals - bright colors were for primates - fruit developed to protect seeds and co-evolved
leaves - megaphylls (Vascular Plants)
branched vascular network
Sepals
green, enclose the flower
Hyphae
multicellular, thread-like structure in a fungus that resembles the root of a plant - mycelium is a network of hyphae
Leaves (Vascular Plants)
surface area for photosynthesis
Bryophytes
- collection of early diverging lineages (not a clade) - lack complex vascular system (ancestral character) - no way to transport food and water over long distances - includes liverworts, mosses, and hornworts - use rhizoids, not true roots (can't take up water/minerals) - absorption occurs directly through cell membrane - gametophyte dominant - sporophyte dependent on gametophyte - flagellated sperm defendant on water
sporophyte dominant
- dominant in vascular plants - spends most time as sporophyte - early plant is that water is needed for reproduction
Types of mycorrhizal fungi
- ectomycorrhizal fungi ---> hyphae on surface of roots - arbuscular mycorrhizal fungi ---> extend branching hyphae into plant cell walls through tubes provided by the plant
Mycorrhizal Associations are Ancient
- fossils from 405MYA - three genes in plants required to form mycorrhizal associations --> found in all major plant lineages - mycorrhizae present in common ancestor of all land plants
Glomeromycetes
- from abruscular mycorrhizae - symbionts with plants
Ascomycetes
- live in marine, freshwater, and terrestrial habitats - ascomycetes produce fruiting bodies called ascocarps
cuticle
a waxy covering of the epidermis that functions in preventing water loss and microbial attack
Ovary
holds ovules -- will develop into fruit - seeds develop from ovules after fertilization - the ovary wall thickens and matures to form a fruit - fruits protect seeds and aid in their dispersal
Petals
may be brightly colored - attract pollenators
Phloem (Vascular Plants)
transport sugars, amino acids, and other organic molecules
Yeasts
unicellular fungi
leaves - microphylls (Vascular Plants)
small, spine-shaped, single vessel
Carpels
make ovules
Endophytes
- fungi living inside tissues of plant that benefit host - may produce protective toxins --- deter herbivores
Basidiomycetes
-decomposers -Ectomycorrhizal fungi -long-lived heterokaryotic stage ---multiple nuclei in each cell -mushrooms!
sphorophyte
forms after the sperms and egg of a plant bind
Fungal Diveristy
- Chytrids (1,000 species) - zygomycetes (1,000 species) - glomeromycetes (160 species) - Ascomycetes (65,000 species) - basidiomycetes (30,000 species)
Connection of Fungi, Animals, and Plants
- although not closely related, plants and fungi colonized the land as partners before animals arrived - plants supply oxygen and synthesize organic molecules - fungi break down organic material and recycle nutrients
Pollinators
- animals visit flowers, transfer pollen to other flowers - angiosperm clades with bilaterally symmetrical flowers have higher rates of speciation --- flowers restrict animal movement, making visits to other flowers more likely
Vascular Plants
- bryophytes were the prevalent vegetation during the first 100 M years of plant evolution - the earliest vascular plants date to 425 MYA - Vascular tissue allowed for increased height, which provided an evolutionary advantage --- sunlight and spore dispersal
Fungal Reproduction
- can be sexual or asexual - use spores
Biotic interactions
- can benefit both species involved (mutualism) or be beneficial to one species while harming the other (parasitism) - Plants and fungi had large effects on biotic interactions because they increased the available energy and nutrients on land
Ancestral Alga
- charophytes are closely related to plants - shared characteristics which make it essential to move onto land - must have some support structure, dehydration, fighting gravity (stronger gravity on earth than water) = must work around
The greening of Earth
- for more than the first 2 B years of earth's history - terrestrial surface was lifeless - cyanobacteria and protists likely exhausted on land 1.2 BYO - around 500 MYA, small plants, fungi, and animals emerged on land - first forests formed about 385 MYA - everything initially existed in some water, but then transitioned onto terrestrial territory - fossil evidence about transition to land - through creating biofilms and clusters
Early Plants
- fossil evidence indicates that plants were on land at least 470 MYA - fossilized spores and tissues have been extracted from 450-MYA rocks - Large plant structures, began around 425 MYA - by 400 MYA, a diverse assemblage of plants lived on land - unique traits in these early plants included specialized tissues for water transport, cuticles, stomata, and branched sporophytes
gametophyte
- haploid that produces haploid gametes by mitosis
Fungi
- heterotrophs - don't eat -- absorption -- secrete enzymes outside the body -- living and dead food sources - rigid cell wall (chitin = would burst without it) - body forms (yeasts, hyphae)
Adaptations Enabling the move to land
- 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 sunlight, more plentiful CO2, and nutrient-rich soil - land presented challenges: a scarcity of water and lack of structural support -acculumation of traits that facilitated survival on land may have opened the way to its colonization by plants - define plants as embryo-bytes, plants with embryos
derived traits of plants
- key traits that appear in nearly all land plants but are absent in the charophytes included -- alternation of generations -- multicellular, dependent embryos - walled spores, produced in sporangia - apical meristems
Evidence of Algal Ancestry
- many characteristics of land plants also appear in some algae - however land plants share certain distinctive traits with only charophytes, including: --- rings of cellulose-synthesizing proteins ---structure of flagellated sperm --- sporopollenin - prevents structure from drying out (charophytes protect zygote; plants protect haploid spores)
Most Abundant Seedless Vascular Plants
- most abundant in the Carboniferous period (359-299 MYA) - Early seed plants rose to prominence at the end of the carboniferous period - near the end, seed plants grew to be more dominant -> which was tied to water and the climate which they were dealing with
Seed Plants
- originated about 360 MYA - Adapted for spreading on land - Seed - Embryo, food supply, protective coat - seed dispersal (wind of other means) - reduced gametophytes, ovules, and pollen --- microscopic gametophyte develops inside the sporangium of parent --- pollen includes male gamete enclosed in protective wall of sporopollenin --- capable of long distant travel
Carbon Cycling
- plants draw CO2 from atmosphere --- produce organic compounds - first widespread forests --- reduced atmospheric CO2 levels --- initialed a glacial period
Terrestrial Plants
- plants make up the habitats of animals and many other organisms - plants affect soil formation; their roots stabilize the soil and decaying plant parts add nutrients - much of the oxygen present in Earth's atmosphere was released by photosynthesizing plants - atmosphere chaining because of plants - plants and fungi affect the cycling of chemicals in the ecosystem - plants absorb nutrients, which are passed on to the animals and eat them - decomposers, including fungi and bacteria, break down dead organisms and return nutrients to the physical environment
Fungal Sexual Reproduction
- plasmogamy = fusion of cytoplasm of two parent mycelial cells - karyogamy = nuclei of the two parent cells fuse (may happen hours or centuries later) -- zygotes produces haploid spore by meiosis (need optimal environment to survive and live) = go through meiosis
Zygomycetes
- rapid growing hyphae - decomposers (many food "molds") - red molds
Earliest Land Plants
- simple branching photosynthetic stems - short and small - first appeared 400 MYA - algae and charophytes carried out gas exchange through membrane - terrestrial adaptations included cuticle and stomata - no true roots = rhizoids only anchor the plant to the substrate
alternation generation
Fern: - young gametophyte - one makes egg and one sperm = fertilization for zygote -- water for sperm -- main structure of the plant -- spores on the bottom of leaves, scattered in the forest and form new gametophyte
Extant Seed Plants - Clades
In seed plants: Gymnosperms Angiosperms
Plant- Animal Interactions
animals influence the evolution of plants and vice versa - ex. animal herbivory selects for plant defenses - ex. interactions between pollinators and flowering plants select for mutually beneficial adaptations
Floral Organs
Sepals Petals Stamens Carpels Ovary
Xylem (Vascular Plants)
conducts water and minerals - includes tube-shaped cells called tracheids - water conducting cells are strengthened by lignin and provide structural support
Charophytes
green algae that are the closest relatives of land plants - works with tide that goes in and out - some drying potential - able to stay hydrated - to prevent dehydration = more successful - able to select genes and move onto land
Gymnosperms
have "naked" seeds that are not enclosed in chambers - includes conifers & cycads - better suited than nonvascular plants to drier conditions due to adaptations including (seeds and pollen; thick cuticles; leaves with small surface area) - less area for evaporation = contain moisture - advantage for colder climate
Angiosperms
have seeds that develop inside chambers called ovaries - produce flowers and fruit - flower = sexual reproductive structure of angiosperms - may or may not involve pollinators - composed of floral organs --- modified leaves
Seedless Vascular Plants
lycophytes (club mosses) monilophytes (ferns) - early form of vascular plants
Roots (Vascular Plants)
organs that absorb water & nutrients from soil -- anchor plant - roots begin the change - roots evolved because of a transport system - plant can transport nutrients and water move, plus holds for stability
radial symmetry
pollinator at any angle - large amount of gene flow
Stamens
produce pollen - pollen with stay on the stigma of the other plant - pollen tube down stigma and fertilizes