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