VASCULAR PLANTS, TEST 1

How did photosynthesis change conditions on earth

early photosynthetic organism used sunlight to make organic molecules, in the process they split water and released O2

• initially a lot of this O2 reacted with dissolved iron in the oceans, producing iron oxides, eventually around 2.2 billion years ago oxygen began to accumulate in the atmosphere

• photosynthesis → O2 production → oxygen-rich atmosphere

Great oxidation event

the major accumulation of free O2 in Earth’s atmosphere due to photosynthetic organisms

• O2 began accumulating about 2.2 billion years ago, and atmospheric increased substantially afterward

• completely changed what kind of organisms could survive and evolve

• ultimately caused by oxygen-producing photosynthesis

formation of the Ozone layer

once enough atmospheric O2 accumulated, some O2 molecules in the upper atmosphere were converted into ozone (O3)

• ozone absorbs harmful UV radiation from sunlight

• by approximately 450 million years ago, the ozone layer provided enough UV protection for organisms to survive at the surface and helped make the colonization of land possible

O2 accumulation → O3 formation → UV protection → life on land becomes possible

Aerobic respiration possible through what

increasing atmospheric oxygen also allowed organisms to use aerobic respiration

• aerobic respiration uses oxygen to break down energy-rich organic molecules

• aerobic respiration can extract far more energy from organic molecules than anaerobic processes

photosynthesis → O2 → aerobic respiration → much more efficient energy extraction

limiting factors in the aquatic environment

early photosynthetic organism lived in water, as their populations increased they used up resources (Carbon, Hydrogen, Oxygen, essential minerals/nutrients, light limited in deeper water)

• encouraged organisms to become more abundant near shorelines, where rivers and streams continuously supplied minerals and nutrients

challenges of the terrestrial environment

land provided abundant light, CO2, O2, and mineral-rich soil, but the major problem was water

• water is the critical factor in the transition from water to land

• plants needed ways to obtain water → transport water → prevent water loss

• needed structural support because water was no longer supporting their bodies

adaptations to terrestrial life

structures evolved to solve these problems

• roots: anchor the plant and collect water and minerals from soil

• stems: provide structural support and raise photosynthetic organs toward sunlight

• leaves: became the major organs for photosynthesis

• vascular tissue: transports substances throughout the plant

• epidermis: covers the aboveground plant

• waxy cuticle: covers the epidermis and reduces water loss

• stomata: pores controlled by guard cells that allow gas exchange while helping regulate water loss

xylem vs. phloem

both vascular tissues used for transport of substances

• xylem: water and minerals primarily upward from roots

• phloem: products of photosynthesis such as sugars throughout the plant

reproductive adaptations to land

• drought resistant spores: one of the earliest reproductive adaptations to land

• multicellular reproductive structures: games/reproductive cells were protected from drying by surrounding sterile cells

• later seeds provided even greater protection (embryo, stored food, seed coat)

water balance challenges and adaptations

plants face a trade off: they need to conserve water but they also need to exchange gases with the atmosphere

• cuticle: reduces water loss but a completely sealed surface would prevent gas exchange necessary for photosynthesis and respiration

• stomata is the solution, with guard cells for regulation

cuticle → conserve water

stomata → controlled gas exchange

guard cells → open/close stomata

Phylogenetic trees/cladograms

represents evolutionary relationships and common ancestry

• node: represents a common ancestor/branching event (speciation event)

• clade: branch on tree of life with original taxon and all descendent taxa

• monophyletic: an ancestor and all descendants

• polyphyletic: descendants from multiple branches, not ancestor

• paraphyletic: includes common ancestor and some descendants

asexual reproduction

involves one parent and does not involve fusion of gametes, offspring are generally genetically identical to the parent so they are essentially clones

• ex: vegetative growth (through stolons and rhizomes, strawberries and aspens), plantlets developing along leaf margins (mother of thousands), apomixis (asexual production of seeds)

• advantages: fast, requires one parent, uses less energy/resources, offspring suited to parents environment

• disadvantages: low genetic diversity

sexual reproduction

the production and combination of gametes, an egg and sperm joining during fertilization

• advantages: high genetic diversity

• disadvantages: requires time and resources and specialized reproductive structures (flowers, fruits, cones, nectar), offspring may be small and vulnerable

alternation of generations

plants alternate between two multicellular generations (gametophyte = haploid (1n), sporophyte = diploid (2n))

• the cycle repeatedly switches between the two

• sporophyte (2n) → (meiosis) spores (1n) → (mitosis/growth) gametophyte (1n) → (mitosis) gametes (1n) → (fertilization) zygote (2n) → (mitosis/growth) sporophyte (2n)

gametophyte generation

haploid (1n) gamete-producing generation, developed from a haploid spore

• because the gametophyte is already haploid, it produces gametes through mitosis not meiosis

• Archegonium → produces egg

• Antheridium → produces sperm

• combined creates the zygote which grows through mitosis into the sporophyte

sporophyte generation

diploid (2n) spore-producing generation, which develops from the 2n zygote

• sporophyte contains structures called sporangia, where spores are produced

• sporophyte (2n) → sporangium → (meiosis) spores (1n) (then grow through mitosis into haploid gametophytes)

• gametophyte → gametes by mitosis

• sporophyte → spores by meiosis

moss alternation of generations

mosses are different from vascular plants

• gametophyte (1n) dominant

• sporophyte (2n), short lived and attached/dependent on the gametophyte

• water dependent fertilization because sperm must travel through water to reach the egg

fern alternation of generations

ferns show an evolutionary shift

• sporophyte (2n) dominant, free living and can persist for many years

• gametophyte (1n) free living but much smaller and short lived (1-12 months)

• water dependent fertilization

gymnosperm alternation of generations

includes pines, cycads, ginkgo. even greater shift towards sporophyte

• sporophyte dominant (2n)

• gametophyte (1n) greatly reduced and are no longer large, independent plants, they remain associated and dependent on the sporophyte

• fertilization is not water dependent, sperm reach the egg through the pollen system/pollen tube

angiosperm alternation of generations

angiopserms are flowering plants

• sporophyte (2n) is dominant

• gametophytes are greatly reduced

• fertilization is not dependent on external water because pollen allows sperm to reach the egg

dioecious

male and female reproductive structures occur on different individual plants

ex. Ginkgo, cycads, aspen

monoecious

a single plant produces both male and female reproductive structures

ex. oaks and pines

bisexual

a single flower contains both male and female reproductive structures

• occurs in many angiosperms

bryophytes vs. polysporangiophytes (vascular plants)

• bryophytes: gametophyte dominant, sporophyte is small and nutritionally dependent, usually one sporangia, no true xylem/phloem, no true roots/ stems/ leaves, little structural support

• polysporangiophytes: sporophyte dominant, sporophyte is large (branched) and free-living, many sporangia, xylem and phloem present, true roots/stems/leaves, lignin in cell walls provides support and allows taller growth

vascular tissue organization

• protostele: solid central core of vascular tissue, no pith, found in roots and lycophytes

• siphonostele: vascular tissue surrounds a central pith, leaf traces may leave leaf gaps which are common in ferns

• eustele: separate vascular bundles arranged in a ring around a pith, found in seed plants

leaf evolution

• microphylls: usually small leaves with one unbranched vein and no leaf gap, characteristic of lycophytes, likely evolved as small stem outgrowths called enations

• megaphylls: generally larger leaves with branched veins and leaf gaps, evolved from branching systems through overtopping, plantation, and webbing. found in ferns, horsetails, and seed plants

reproductive systems

• oogamy: large nonmotile egg is fertilized by a small motile sperm

• heteromorphic alternation of generations: multicellular haploid gametophyte and multicellular diploid sporophyte which look different

• sporophyte is dominant in vascular plants ; gametophytes are reduced

• fertilization still requires water because flagellated sperm must swim to the egg

homospory vs heterospory

• homosporous: one type of spore; usually produces a bisexual gametophyte with both antheridia and archegonia

• heterosporous: two spore types, microspores (male gametophytes) and megaspores (female gametophytes that are smaller, unisexual, and usually develop inside the spore wall)

primary vs secondary growth

primary: lengthening of roots and shoots, occurs at apical meristems

secondary: thickening of roots and stems, occurs at lateral meristems (vascular cambium makes secondary xylem and phloem, cork cambium produces periderm which replaces the epidermis)

Lycopodiacea, Phylum Lycopodiophyta

• club mosses

• Homosporous

• Microphylls

• sporophylls may form a cone called strobilus

• gametophytes are often bisexual and may be underground/mycorrhizal

Selaginellaceae, Phylum Lycopodiophyta

• spike mosses

• Heterosporous

• produce microspores and megaspores

• have a ligule, small scale-like outgrowth near the upper surface of each microphyll

Isoetaceae, Phylum Lycopodiophyta

• quillworts

• Heterosporous

• often aquatic or grow in seasonally wet soil

• have a corm and quill like microphylls

• also have ligules

Phylum Monilophyta classes

class Psilotopsida: whisk ferns and adders tongue ferns, eusporangiate

Marattiopsida: large tropical eusporangiate ferns

Equisetopsida: horsetails, joined stems, whorled branches, and strobili

eusporangia vs leptosporangia

eusporangia: develop from several initial cells, have thick walls and produce many spores

leptosporangia: develop from one initial cell, have one cell thick wall, usually produce 64 spores, and often contain annulus for spore release

seed definition and advantages

a mature ovule containing a diploid embryo (young sporophyte), stored food, and a protective seed coat

• seeds are better than spores because they protect and nourish the embryo, allow dormancy until conditions are good, and disperse the developing sporophyte instead of only one cell

key evolutionary changes that produced seeds

• all seeds are heterosporous: produce microspores and megaspores

• the megaspore is retained within the megasporangium

• only one of the four megaspores survives

• the female gametophyte develops within the retained megaspore and is not free-living

• embryo develops within the female gametophyte

• integument surrounds the megasporangium, leaving an opening called the micropyle

• the megasporangium/ovule evolves to receive pollen, allowing fertilization without free water

• the dispersal unit becomes a seed, not a spore

progymnosperms

extinct seedless vascular plants considered precursors to gymnosperms, they had secondary growth from a bifacial vascular cambium, producing secondary xylem inside and secondary phloem outside, but reproduced using freely dispersed spores rather than seeds

Phylum Coniferophyta

leaf: needle or scale-like leaves, sex arrangement: mostly monoecious, sperm: nonmotile, ex: pines, firs, spruces, redwoods

Phylum Cycadophyta

leaf: large, pinnately compound leaves, sex: dioecious, sperm: motile multiflagellated, ex: cycads

Ginkgophyta

leaf: fan shaped leaves with open dichotomous veins, sex: dioecious, sperm: motile multiflagellated, ex: ginkgo biloba only

Gnetophyta

leafs: variable, often broad leaves or scale-like leaves, sex: usually dioecious, sperm: non-motile, ex: Ephedra, Gnetum, and Welwitschia

pine reproduction

pines are monoecious (the same tree makes pollen cones and ovulate cones)

• a pollen cone produces microspores which develop into pollen grains (male gametophytes)

• pollen reaches an ovulate cone by wind pollination

• in the ovule a megaspore mother cell undergoes meiosis making four megaspores, three degenerate and one survives

• surviving megaspore undergoes mitosis and develops into the female gametophyte/megagametophyte which contains archegonia and eggs

• the pollen grain grows a pollen tube through the nucellus to the egg

• the generative cell forms two nonmotile sperm, one fertilizes the egg and the other degenerates

• zygote becomes an embryo, the mature seed contains the embryo, female gametophyte food tissue, and seed coat (it takes about two years for pines to produce a mature seed)

major conifer families

• Pinaceae: pines, needles usually occir in fasicles/bundles

• Taxaceae: yews, seeds are surrounded by a fleshy red aril not a typical woody cone

• Cupressaceae: cypresses, junipers, redwoods, scale like or awl like leaves are common

• Araucariaceae: includes wollemia nobilis, primarily southern hemisphere

Phylum Cycadophyta, Cycads

cycads are dioecious plants with palm-like pinnately compound leaves, they produce motile, multiflagellated sperm, their seeds are often toxic, and some are pollinated by beetles, male cones resemble corn cobs

Phylum Ginkgophyta, Ginkgos

Ginkgo biloba is the only living Ginkgo species, it is dioecious, has fan-shaped leaves, and produces motile multiflagellated sperm, female plants make fleshy seeds that smell bad because of butyric acid, male trees are usually preffered for landscaping

Phylum Gnetophyta, Gnetophytes

non-motile sperm delivered through a pollen tube, some including Ephreda show a form of double fertilization but it does not produce true triploid endosperm like in angiosperms

basal grade angiosperms

earliest diverging groups, including Amborella, water lillies, and Austrobaileyales. They are called a grade because they are not one single clade

Magnoliids

include magnolias, laurels, pepper plants, and relatives. Many retain ancestral-looking traits such as numerous floral parts

Monocots

one cotyledon, parallel leaf veins, scattered vascular bundles, fibrous roots, flower parts usually in multiples of 3, and pollen with one opening

dicots (eudicots)

two cotyledons, netted leaf veins, vascular bundles in a ring, usually a taproot, flower parts usually in multiples of 4 or 5, and pollen with three openings

Perianth

the nonreproductive outer flower parts

• calyx: all sepals, usually green and protective

• corolla: all petals, often colored and attracts pollinators

Gynoecium

the female reproductive whorl; all carpels of a flower

carpel

female reproductive structure consisting of 4 parts

• stigma: sticky tip that receives pollen

• style: stalk through which the pollen tube grows

• ovary: enlarged base containing ovules

• ovules: develop into seeds after fertilization

Androecium

the male reproductive whorl; all stamens of a flower

stamen

male reproductive structure consisting of 2 parts

• anther: produces pollen

• filament: stalk supporting the anther

microsporogenesis

meiosis occurs in the anther’s microsporangia. a diploid microsporocyte produces four haploid microspores

microgametogensis

each microspore develops by mitosis into a pollen grain, the male gametophyte

• a pollen grain contains a vegetative/tube cell and a generative cell, the generative cell divides to form two sperm cells

megasporogensis

meiosis occurs in the ovule, one diploid megasporocyte produces four haploid megaspores; usually three degenerate

megagametogensis

the remaining functional megaspore undergoes mitosis and develops into the embryo sac, the female gametophyte

• the typical mature embryo sac has seven cells and eight nuclei (one egg cell, two synergids, three antipodal cells, one central cell with two polar nuclei)

pollination

transfer of pollen from an anther to a stigma

• after pollen reaches a compatible stigma it germinates and grows a pollen tube down the style to an ovule

• the tube delivers two sperm cells into the embryo sac

double fertilization

one sperm fertilizes the egg → diploid zygote which becomes the embryo

• the other sperm fuses with the two polar nuclei → triploid endosperm which nourishes the embryo

• the ovule becomes a seed and the ovary becomes a fruit

5 trends in floral evolution

1. flowers changed from many, indefinite parts to fewer parts in definite numbers

2. the floral axis became shorter, placing flower parts closer together

3. ovaries often became inferior instead of superior

4. radial symmetry often changed to bilateral symmetry

5. floral parts frequently became fused or specialized for particular pollinators

floral traits and pollination vectors (8)

1. beetles: open bowl shaped flowers, often strong fruity, spicy, yeasty odors, provide pollen and or nectar

2. flies: dark red or purple or brown, may smell like rotting meat or carrion, some mimic places where flies lay eggs

3. bees: blue, yellow, UV marked nectar guides, landing platforms, sweet scents and nectar

4. butterflies: bright colored flowers, often with a landing platform and nectar in narrow tube

5. moths: pale or white flowers that commonly open at night, strong sweet scent, long floral tubes or spurs

6. birds: usually red, orange, or brightly colored tubular flowers with lots of nectar, little odor

7. bats: large, sturdy, pale flowers that open at night, strong odor and abundant thin nectar

8. wind: small inconspicuous flowers with no scent or nectar, produce huge amounts of lightweight pollen, exposed anthers and feathery stigmas

fruit traits and dispersal vectors (6)

autochory (self-dispersal)

• barochory (dispersal by gravity, heavy round fruits) or ballochory ballistic (explosion of fruit)

Allochory

• wind (anemochory): small lightweight fruits or seeds with wings, hairs, plumes, or parachute-like structures

• water (hydrochory): floating fruits (coconuts), waterproof skin

• animals (zoochory): epizoochory (external): dry fruits with hooks, spines, barbs, or sticky structures that attach to fur or feathers, endozoochory (internal, eaten): fleshy, colorful, sweet, nutritious fruits; animals eat them and disperse seeds in droppings

• caching: gather seeds and store them underground/surface/ground