Biology 201 Final Review: Aarssen Lectures 1-12 + Grogan Fungus Lectures
- Origin, Evolution and Classification of Land Plants.
- The link between life and non-life, photosynthesis: the conversion of light energy and
fixation of carbon, chemical energy, carbon skeletons, oxygen
- Invasion of the land: the “Blob”
- Simple design of photosynthesis machines, mitosis to grow laterally across soil:
minimized wind exposure, maximized water absorption and light uptake.
- Spongiophyton: no vascular tissue, all surface cells are photosynthetic , pores to
- Why is there no Blob
- i) mechanical constrains: requires continuous uptake of water and minerals from
soil. ii) Inherent limits to tolerance of environmental variation: cannot have one plant
that is adapted to live in all conditions. iii) inherent limits to longevity: immortality if
possible for very few multicellular organisms.
- Why is there diversity
- Mutation: genes are subject to random change; beneficial mutations will remain in a
population and begin speciation. These include: Changes in physiological
tolerance( exploitation of different environments), Roots( more reliable and deeper
extraction of water and minerals), Small propagules(small structure that detachs from
the main plant to give rise to new plants)( allows dispersal over land and have a
protective covering), Increased height( increases light uptake against competition,
and dispersal of propagules).
- Meristems: where mutations accumulate because it is the site of genetic processes:
consists of undifferentiated cells, the way plants have evolved certain phenotypes is
dependent on meristem function.
- Evolution by natural selection: i) there is a variation in traits between individual
organisms due to differences in genetic material that originate initially as mutation. ii)
these genetic differences are inherited. iii) some heritable differences are responsible
for differential survival and reproduction( goal: to make symgamy and meiosis
happen, without species has high risk of extinction)
- Mutation variation natural selection evolution organic diversity.
- Acquiring genetic variability: the role of sex - Since the environment is not homogeneous, it only makes sense that there is a
mixture of genetic types.
- Two ways to have genetically variable offspring: i) acquire different mutations in
different mitosis centers(meristems) all the cells produced there will have said
mutation ( this is very slow). ii) make new combinations of genes by sexual
reproduction, independent assortment of chromosomes and crossing over are
present in meiosis ( instead of mitosis).
- Advantage of sex required getting ‘small’ during some point( for genetic
recombination and dispersal of propagules) since combining genes happens during
the fusion of two gametes ( haploid) to form the zygote(diploid) . They also need to
get tall for success in competition for light and greater dispersal of seeds.
- Sexual cycles and alternation of generations in land plants
- Three types of cycles: Zygotic, Gametic, and Sporic
- The Origin of Alternation of Generations or Sporic meiosis.
- Two similar eukaryotic(haploid) cells mate and for a 2n zygote, initiation diploidy and
providing two advantages: i) allows sex ( more variability) and ii) protection against
deleterious mutations ( dominance and sexual selection acts as a sieve)
- Some evolutionary lines elaborate the haploid generation, and others the zygote.
The mani evolutionary line was toward alternation , from the sygotic pattern by delay
in meiosis until the multicellular diploid generation had developed so that both
generations are multi-cellular.
- Origin of Land Plants
- Algal ancestors: chlorophyta ( green algae) has the same pigments, stacked
thylakoids and starch storage products as higher plants. The class charophyceae
have the same :phragmoplast at cytokinesis, sterile sheath of cells surround the
gametes, oogamous ( large female games, small male gametes), zygote is formed
and retained in the plant.
- Stages in the evolution series from algae to early land plants: fertilization within
oogonium from zoospores Mc diploid and emergent sporangium cuticle forms
around portion out of water and spores are released the byrophytes ( early land
plants ) begin to develop early vascular plants form roots, and conduction tissues to
obtain and distribute water.
- Classification of the land Plants:
- Thallophytes : lower plants ; Fertilization outside the plant and no embryo ( algae
fungi and slime molds) - Embryophytes: higher plants/land plants, fertilization occurs within the plant, embryo
developes and is retained within the plant. They include bryophytes and
- Bryophytes: not very tough , very weather sensitive. phylums: Anthocertophyta
(Hornworts), Marchantiophyta( liverworts) bryophyte (mosses).
- Tracheophytes: produce tracheal tissue ( vascular plants) include the pteridophytes
(non-seed plants ) Lycopodiaphyta (club mosses)& monilophyta (whisk ferns, ferns
and horsetails.) and the spermatophytes (seed plants ) gymnosperms( non-flowering,
Cycads, Ginkgo, Conifers, gnetophytes) and the angiosperms( flowering plants)
Lecture 2: The Byrophytes
- General Characteristics
- non-vascular, gametic metois, anchored to substrate with rhizoids: these do not
partake in water of nutrient conduction. They absorb water and inorganic ions directly
through the gametophyte surface. Dries up and becomes dormant in absence of
water, and resumes growth when water becomes available again. Very resistant to
dessication, can survive for long periods without water. They possess a sterile jacket
of cells surrounding gametes( to protect them from desiccation). Gametes
( antheridium = male gametangia, archegonium = female gametangia) produced in
haploid phase, sperm needs water to be able to reach the egg. Vegetative
reproduction by the gemmae, asexual reproduction by fragmentation or by using the
gemmae to self fertilize and produce new gametophytes.
- Liver worts
- Thallose liverworts: most common, undifferentiated , grows on moist soil and rocks,
dichotomous: 2 branches ( Marchantia), unisexual gametophytes( each gametophyte
only produces one of either sperm or eggs). The sporangium’s entire purpose is to
make a sac for meiosis to occur.
- Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium meiosis.
- Leafy Liverworts: photosynthetic tissue( no vascular tissue so not true leaves), grow
on the leaves and bark of trees in humid or moist environments, most common in the
- Spore discharge in the liverworts: involves elators( hygroscopic: change in response
to humidity/ moisture) sporangium splits open when dry/mature, and releases
hundreads of spores. Contains nostoc ( a cyanobacterium) embedded in mucilage,
cells in the thallus including the epidermis screte mucilage which is essential for
water retention. Most gametophytes are unisexuals, some are bisexual. - Hornworts
- Anthoceros: the genus name for most if not all hornworts. Resemble thalloid
liverworts, bisexual gametophytes, archegonia and atherida embedded within the
thallus, undifferentiated flat thallus ( blob), long sporangium: upright elongated
structures with a cylindrical capsule at the tip and a foot at the base. columella:
central column of sterile cells( maybe an ancestor of higher plants as this is similar to
a stem). Foot penetrates the gametophyte tissue and forms a placenta across which
the sporophyte obtains nourishment from the gameophyte, during development a
basal meristem( active in favorable condtions) between foot and meristem, helps
elongate sporangium. All stages of spore development from meiosis near the base to
mature spores above can be seen in a single sporangium.
- Classes: Bryidae( true mosses) , Sphagnidae (peat mosses), andeaeidae( granite
- Bryidae: stem structure, not quite as good at transport as vascular tissue, seta =
stalk, hydroids(kinda like xylem, doesn’t look like it but still conducts water) lack
lignin( permeable and thin) , polytrichum: gametophyte “stem” cross section with
central conductuing tissues. Leptoids are kinda like phloem( transports
photosynthates, more so than the rest of the stem structure). Variety in peristomes:
ring of teeth, movements of teeth in response to splitting cell layer near capsule in
dry environents releases spores to be dispersed by wind.
- Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium meiosis.
- Sphagnidae: sexual reproduction involves formation of antheridia and archegonia at
the ends of special branches at the tips of the gametophytes. Sporophytes: capsules
with short stalk are attached to the pseudopodium ( remainder of the stalk-
gametophyte). Unsual protonema: first stage of development of the gametophyte –
does not consit of multicellular branced filaments like most mosses- just a plate of
cells that grows by a marginal meristem, in which most of the cells can divide in one
of only 2 directions.
- Spore Discharge in mosses: as capsule dries it contracts changing from a spherical
to a cylindrical shape and compresses trapped gas within the capsule. This gas
reaches high pressure and blows off the operculum( lid on the top of the sporophyte
capsule) with the explosive release of spores.
Lecture 3: Vascular plants
- No plants made seeds 300million years ago or flowers. - World became crowed with land plants so it was harder to compete for light, had to
get tall. Most common reason for extinction is because they failed at this life cycle,
did not have successful gamete production and syngamy.
- Evolved roughly 400mya. In the beginning of the land plant the picture would be
made up of bryophytes and vascular plants.
- The dominate generation in vascular plants is the sporophyte ( sporangium produced
on sporophyte which houses spores to keep cycle going).
- First land plants ~400mya , no photosynthesis, nothing in the terrestrial environment
would evolve with them, they produced oxygen, set the stage for fossil fuels, oxygen
atmosphere and the evolution of animals.
- Theory one: algae split into Bryophytes( still around , small and successful) and
Tracheophytes( they really provide most f the carbon build up that allows for fossil
fuels and oxygen). Xylem= transports water and nutrients upwards and provides
physical support. Phloem: transports sugars and proteins.
- Theory 2: usually use fossil record if we have it, we can use inference, piecing
together a hypothesis based on debate. Anthoceros-like ancestor Vascular plants.
Similarities : i) sporophyte has a central columella which may have easily evoloved
into a internal conductive system of xylem and phloem ( sterile) ii) sporophyte has
cutile and stomata with guard cells. ( stomata controls entry of CO2 and release of
water)) iii) sporophyte has an intercalary meristem which provides indeterminate
growth ( important in higher plants, here the sporophyte continues to grow , pushing
up the sporophyte )
- The First Vascular plants and early evolution.
- The oldest fossil plant is the cooksonia.
- Three extint phyla : common features include no roots, no leaves, cuticle ,
dichotomously branching stem , sascular tissue was a protostele, and they were
- Rhyniophyta: Cooksonia(Most of the tips of the dichotomies produce sporangium) ,
Rhynia(produce vegetative and sporangium on tips, more specialized), &
Homeophyton( sporangium are in cluseters on tips).
- Zosterophyilophyta: Sporangium, where meiosis takes place. Evolution is bringing
them to a localized place to keep them together and protected, didn’t have leaves
but had to increase surface area to capture light, didn’t have leaves but had to
increase surface area to capture light , photothesis takes place in stem. Some had
spine like outgrowths roviding increase surface area for light harvesting. - Trimerophyta: larger with a main axis ( 1-3m tall), increased diameter of stele,
increased xylem lignification( gives added structural support), lateral brances
specialized in photosynthesis, clusters(grouping of sporangia).
- Major Evolutionary trends in Vegetative traits
- Roots: Reliable water source is in the ground, vascular plants at first did not have
roots, worked out OK but not great. Early vascular plants had rhizomes with only
rhizoids functioning only for attachment to the substrate specialized rooting organs
with vascular tissue.
- Evolution of the Axis: A) increase in height: dichotomously branching sympodial
axis( zig zag) monopodial axis( straight center). B) Increase in girth: evolution of
thicker, heftier branches, thinckened girth stem with vascular tissue, the tissue that
gives it the strength is around the outside, greater strength per mass ( prevents
falling over and being top heavy).
- Evolution of Vascular Tissue: A) evolution of the siphonostele, protostele
siphonostele eustele. B) Evolution of xylem tracheid cells and xylem vessel:
increasing amount of secondary wall thickening ( lignin) C) Secondary Growth:
secondary growth from vascular cambien, a secondary lateral meristem allowing
greater increase in stem girth. M cambium ( intiated by the primary cortex) cork
(phellum, toward the outside and dies to form protective layer) and secondary
cortex(phelloderm, towards the inside). Replacement tissues to replace damaged
tissues as growth pushes outwards. Allows fore more vertical growth.
- Evolution of the leaf: A) origin of the microphyll, increased SA for gas exchange,
outgrowths of cortex and epidermis, later extension of vascular tissue, reduction of
dichotomous branches( these shoots become a microphyll that serves the function of
not producing sporangium but adding more SA B) origin of the megaphyll: 3-D
arrangement of dichotomous branches flattened arrangement in a single plane
filling in of space between branches with parenchyme reduction at dichotomies
produces a pinnately veined megaphyll.
- Summary of evolutionof vegetative traits: Obtaining water roots immobility
crowdedness tall height from apical dominance and lignin in support tissues
conducting water up and photosynthesis down & stems buckling support from the
vascular cambium ( xylem and phloem) and stem strength from siphonosteles
rupturing of external cortex , loss of water, pathogen entry and fire damage
expanded outer cortex from cork cambium and bark from cork cambium loss of
photosynthetic function in stem formation of leaves to increase SA in higher areas.
- Major Evolution trends in reproductive traits
- Reduction in size and life span of gametophyte generation and increasing
dependence on sporophyte , not much going on in gametophyte therefore reduction
of size, loss of sperm cell motility. Loss of archegonia and antherida, Homospory heterospory: two kinds of spores produced in two kinds of sporangia and which
develop into separate male and female gametophytes respectively.
Lecture 4: Seedless Vascular Plants
- The ancestors of all these plants were the only plants on eather 300mya ago( have a
long history in fossil records), most of the phyla have gone extinct, the evolution of
seed plants were responsible for many of these phyla extinction.
- Whisk Ferns – order Psilotales (peridophyta)
- Characteristics: underground rhizoids, dichotomous branching, protostele, leaves :
psilotum(none, only scale like outgrowths lacking veins & Tmesipteris( spirally
arranged microphyll-like (with one vein), homosporous. Small gametophyte blob
(green largely undifferernted but has an important role of producing gametes.
Antheridia break open and release sperm, spore must swim to find archegonia, if
they find archegonia on the same plant = selfing, need moisture.
- Origin: Theory one: from Phynia-like ancestors ( No fossil record of psilophyta since
the Devonian period (400mya), where rhynia was found. Theory two: result of
reduction from other pteridophyte groups( as they are less structurally complex then
other pteretophyte groups).
- Interpretation of Psilotum sporangium: inference (don’t really have snapshots of
these throughout evolution. By localizing sporangia, it may have helped during water
shortages and protection against herbivory. Sympodial branching system with
overtopping fertile and sterile branches shortened by reduction contined
shortening and fusion of 3 sporangia 3 lobed sporpangium in axil of reduced sterile
branch. Advantages of lobed sporangium: protection from desiccation and less
conspicuous to consumers
- Similarities between gametophytes and sporophyte : i) both have rhizoids( help plant
attach to substrate) ii) both are radially symmetrical ( dicated by meristemic
growth( archeridia and archeonia ) iii) both have dichotomous branching. iv) some
gametophytes have vascular tissues ( like sporophyte). Biggest gametophyte in
seedless plants, starts as a spore grows into blob structure.
- Implications : suggest that gametophyte of early vascular plants were similar in some
ways to the structure of sporophytes. However later selection: increased sporophyte
size and reduced gametophyte size. ( selection presusres that might limit the
success of sporophytes differed from those that might limit gametophytes.)
- Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium meiosis. Gametophytes are very vulnerable to lack of
moisture so they get smaller to conserve moisture. ( seed plants evolved to solve
this) Sporophyte avoided death without sex by getting bigger - Horsetails – Order Equisetales ( Pteridophyta)
- Characteristic: Extend back to the Devonian period maximum abundance and
diversity in carboniferous period ( 300mya), only one living genus, rhizomes that
have emerged true roots( true roots have xylem and phloem), stems joined with or
without branches at nodes, leaves are microphyll, alternate with brances at nodes,
eventually dry out and photosynthesis occurs mainly in surface layers of the stem,
believe to originated from a reduced of dichotomous branches.
- Stem anatomy: as tissue grows the pith breaks down and becomes just open
air(hollow tubes are stronger per weight than solid) , helps to keep the plant upright,
more photosynthesis occurs in stem( chloroplast packed around epidermis), vascular
tissues is arranged in a ring ( eustele) Has a lot of lignin, nick named scouring rush,
- Reproductive structures: sporangia arranged in a spiral, dangle from plate with
sporangiophore in the middle, Strobilus ( a sporal arrangement of sporagiophores),
have elaters, attached to spore, when they are wet the elator arm like structures
spread out and allows wind to disperse the spore , hydroscopic
- Formation of Sporangiophores: sympodial branching system reduction of branches,
recuraction of sporangial stalks, reduction and fusion of sporangial axes, packs
together sporangiophores. Makes them less conspicuous to consumers in
sporangium, more resistant to dessication.
- Life Cycle: early life sporophyte is dependent on gametophyte but eventually it will
have its own roots, all started in archegonia where successful fertilization allowed for
the production of sporophytes, gametophyte gives rise to young sporangium
,homosporous : 1 kind of sporangium 1 kind of spore one gendered gametophyte.
- Extinct forms: Calamites( up to 20m tall, flourish during the carboniferous period,
only herbaceous species are leaft in the extant flora, massive trees.
- Ferns ( several orders, Pteridophyta )
- Characteristics: largest groups of seedless vascular plants, date back to mid-
devonian , sizes range from 2cm long to 24m tall, stm reduced or exsists as a
creaping rhizome, leaves are megaphylls and called fronds, young leaces are coiled
in the bud and uncoiling is refered to as circinate vernation. Successful clonal
propagation seen in growth of horizontal roots, don’t need sex to make babies,
naked sperm have to find moisture to swim around to find egg.
- Origin: monilophyta have prostele, siphonostel and eustele, 2 rings of phloem =
characteristic feauture of vegetative ferns , suggest it’s the prodiuct of natural
selection , why / how did they evolve? Follows the evolution of the dichotomous
branched , early vascular plants, a lot of ferns were trees mya (having a hefty stem
with vascular tissue would have been important). Ferns bulked up but having tissue grow over bundles of dichotomous branches. Amphiphloic siphonostele= concentric
phloem flanking xylem, Dictoyostele selected for lignin protecting pith.
- Sporangia: sorus= cluster of sporangia, diversity of sorus, used for identifiying
features of different groups of ferns, sori are on adult sporophytes, they are
sporangiophores that contain a cluster of sporangia.
- Origin of fern megaphyll and sporangia position: dichotomously branching
system(sporangia at the tips of branches) straightening of main axis and planation
of reduced lateral fertile branch system ( planation: branch system is now in a plane
as opposed to 3D) webbing gives a leaf-like blade with marginal sporangia.
Megaphyll efficient gas exchange and photosynthesis ( high SA) , key reason ferns
are still around.
- Annulus: pod of spores, cell cack in annulus is moist, evaporates as it gets older
causing it to break open, outer walls are thin, once annulus breaks open there is
further evaporation to catapult the spores out.
- Tree Ferns: Growth is entirely by apical meristem( no vascular cambium, stems
cannot get any thicker ) , Arboresecent forms have gone extinct within all the
seedless vascular plant groups with the exception of ferns, ferns are the only group
that hasn’t lost their trees.
- Fern Allies( club mosses, etc) Largest group , they have their own
- Lycopodium (club moss)
- Characteristics: rhizomes with true roots, dichotomous branches with microphylls ,
variation of the protosteles, most photosynthesis occurs in microphylls but can occur
in stem, homosporous bisexual gametophyte, sporangia on upper surface of leaf-like
sporophyll arranged loosely in a spiral arrangement on a stroblilus at the end of the
branch, sporophyll=microphyll with sporangium
- Interpretation of Sporangium : stalked sporangium above leaf-like outgrowth
sporangium moved to auxiliary position, vascular extension into microphyll
sporangium moved onto adaxial surface of microphyll. Advantages include reduced
desiccation of sporangium, improved more by close packing of sporophylls on a
strobilus and less conspicuous to consumers.
- Arborescent Lycopodiophyta ( tree like): Lepidodendron ( dominant tree), up too 20m
tall, flourished during carboniferous period, only herbaceous speices are still present.
- Selaginella: Heterosporous : different spores produce separate male and female
gametophytes , prevents inbreeding as different sexes are on different
- Gametophytes: Very reduced with no morphological similarity to the sporophyte as in
psilotum, develop endosporally i.e within the confines of the spore wall, megagametophyte also develops while the megaspore is still within the
megasporangium, gametophyte spends it entire life in the ( mega an micro) spore
wall. Flagellated sperm still have to swim to find archegonia
Lecture 5: Evolution of the Seed Plants ( Spermatophytes)
- Appeared in Devonian, exisited throughout the carboniferous (400-300mya),
intermediated between early vascular plants and later gymnosperms, large
gymnosperm like axix with secondary thickening from a vascular cambium, Hence
they were first true “trees” but they produced spores not seeds, they could increase
the girth of the bottom of the tree to support its upward growth.
- Sperm is in a vulnerable stage , but seed plants take care of this, seeded plants
caused the extinction of other less evolved plants by being more successful and
obtaining all the nutrients, gametes produced from gametophytes on different male
and female sporophytes, this allowed for more diversity as it promoted sexual
- In seed plants the entire male gametophyte reaches the ovule, no long need
flagellated sperm to travel through water. Megagametophyte produces eggs and
nourishes the new embryo when it develops.
- Evolution solved the problem of gametes in the seed plants through sporangium
(houses for vulnerable gametes), diploid sporophyte plant produce sporangium
( where fertilization occurs).
- The Seed Habit
- Comparison with Petidophytes: Seedless Vascular: 1 kind of sporophyte (one kinda
of spore), they produce tons of spores (cheap), most of them die out but they only
need one spore to fertilize and spread genetics, exosporal= develops outside the
spore wall. Selaginella: only produces 4 spores, retained within the megaspore wall
(beginnigns of seeded plants), dehiscent= splits open, sporophyte is dominant.
Spermatophytes: rest of the megaspores abort, one remaining megaspore develops
into female gametophyte housed within the megasporangium, sporangium does not
split open, gametophyte spends entire life immersed in the tissue of the sporophyte.
- Two major developments: i) Heterosporyand retention of reduced endosporal female
gametophyte and subsequent embryo within an indehiscent sporangium. ii)
integumentation of megasporagium: the tissue that wraps the gametophyte, provides
protection and nutrition to the developing cell. The seed is the fertilized
ovule( containing the zygote or developing embryo) and the integument becomes the
seed coat. - Interpretation of the integument: The extinct plants look just like ferns, there could be
some relationship, could be the first seed plant to produce integemented
sporangium, dichotomous branching system with fertile and sterile branches
reduction to a single functional megasporangium surroned by sterile b