Lecture 5: Control Structures Computer Programming Control Structure Lecture No. 5.
Lecture #5
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Transcript of Lecture #5
Lecture #5
Plant Diversity I: Non-vascular plants
&Seedless Vascular plants
• 1.2 billion years ago (BYA) – appearance of cyanobacteria on land• 500 million years ago (MYA) – appearance of plants, fungi and animals• more than 290,000 known plant species today• plants inhabit all but the harshest environments
– such as some mountaintops, deserts areas and polar regions• many plants have returned to their aquatic “roots”
– e.g. some species of sea grasses• most present-day plants are terrestrial• presence of plants has enabled other life forms to survive on land
– through their production of O2
Plants and Algae• evolution of plants proposed from algae
– closest relatives are located with the clade Charaophycea
– these share a common ancestor with the clade Chlorophyta – include the green algae
– similarities with algae: • multicellular • photosynthetic autotrophs• cell walls with cellulose• chlorophylls a and b
(Opisthokonta) (Viridiplantae)
Rho
doph
yta
Pla
nts
Chl
orop
hyte
s
Cha
roph
ycea
ns
Red
alg
ae
Met
azoa
ns
Fung
i
Cho
anof
lage
llate
s
Archaeplastida
Ani
mal
ia
Chl
orop
hyta
Fung
i
Pla
ntae
Cha
roph
yta
Unikonta
Ancestral eukaryote
4 key traits of plants– four key traits of plants (and charophyceans)
• provided by not only morphologic evidence but genetic evidence• 1. rose-shaped complexes for cellulose synthesis – both charophyceans
and land plants have rosette cellulose-synthesizing complexes • 2. peroxisome enzymes – peroxisomes have enzymes that help minimize
the loss of organic production as a result of photorespiration
Rosettes
4 key traits of plants– four key traits of plants (and charophyceans)
• 3. flagellated sperm structure – similar to the charophyceans• 4. formation of a phragmoplast = group of microtubules that forms
between the daughter nuclei of the dividing plant cell during mitosis
Adaptations by Land plants• advantages of a terrestrial life:
– stronger exposure to sunlight for photosynthesis– atmosphere offered more CO2 for photosynthesis– soil rich in nutrients– initially relatively few herbivores
• movement onto land would require protection of the zygote from drying out– development of layer of durable polymer called sporopellenin – prevents
exposed zygote from dessication• movement onto land resulted in the development of specific
adaptations– facilitated survival and reproduction on land– e.g. development of a structural system to withstand the forces of gravity– e.g. changes adapting to the relative scarcity of water
• these adaptations have defined the plant kingdom
Adaptations by Land plants• what adaptations are unique to plants?• depends on how you draw the boundary separating plants from algae• some traits are related to terrestrial life
– for the earliest land plants – mycorrhizal associations with fungi for nutrient absorption
– epidermis with a waxy covering called a cuticle– production of secondary compounds that are products of secondary
metabolic pathways• primary metabolic paths produce lipids, carbohydrates, amino acids – not
unique to plants– secondary paths produce compounds such as:
• tannins, terpenes and alkaloids (defense against herbivores and parasites)• phenolics (flavonoids – absorb UV radiation, deter attacks by pathogenic
microbes)
Viridiplantae
Streptophyta
Plantae
Red algae Chlorophytes Charophyceans Embryophytes
Ancestral alga
• Kingdom Plantae contains the plants called embryophytes – plants the develop from embryos
• however, current debate advises some changes – 2 options:– Kingdom Streptophytae – Embryophytes (land plates) + Charophyceans OR– Kingdom Viridiplantae – Embryophytes + Charophyceans + Chlorophytes
• botanists do not use the term phyla when classifying the plant kingdom – use divisions
• currently accepted organization: development of two lineages or divisions: non-vascular and vascular (390 MYA)
• called the Bryophyta (non-vascular) and Tracheophyta (vascular)
Hey guys! How about confusing the issue?
** plants can be divided into 2major categories1. non-vascular2. vascular – subdivided into 2 more categories:
a. seedlessb. seed
KISS: Keep it simple stupid
** plants can be divided into 2 major categories1. non-vascular2. vascular – subdivided into 2 more categories:
a. seedlessb. seed
Land plants: 4 characteristics
• 4 key derived traits found in plants:– 1. alternation of generations & multicellular,
dependent embryos– 2. walled spores produced in sporangia– 3. multicellular gametangia– 4. apical meristems
Mitosis
Spores
Mitosis
Mitosis
Zygote
Gametes
Haploid multicellularorganism (gametophyte)
Diploid multicellularorganism (sporophyte)
MEIOSIS FERTILIZATION
Land plants: 4 characteristics– 1. alternation of generations: alternation between multicellular haploid and
diploid stages in a life cycle• seen also in some chlorophytans (algae) – but not in the charophyceans• these generations must be multicellular!!• haploid stage = gametophyte (haploid) • diploid stage = sporophyte (diploid)• the sporophyte is the mature plant produces haploid spores via meiosis• mitotic division of the haploid spore produces a multicellular gametophyte
which is still haploid!!
Mitosis
Spores
Mitosis
Mitosis
Zygote
Gametes
Haploid multicellularorganism (gametophyte)
Diploid multicellularorganism (sporophyte)
MEIOSIS FERTILIZATION
-sporophytes – multicellular, diploid, produce haploid spores via meiosis-gametophytes – multicellular, haploid, produce haploid gametes via mitosis
Land plants: 4 characteristics– 1. alternation of generations: alternation between multicellular haploid and
diploid stages in a life cycle• the gametophyte is the reproductive part of the plant - produces haploid
gametes by mitosis• gametes fuse via syngamy/fertilization to produce the zygote• zygote grows via mitosis to develop a new sporophyte• in non-vascular plants (like ferns) – the sporophyte and gametophyte have
distinct phenotypic appearances – but they are forms of the same species• in vascular plants – the gametophyte is microscopic
• 1. Alternation of generations and multicellular dependent embryos cont….– in a life cycle with alternation of
generations – the multicellular embryos develop from zygotes are retained within the female gametophyte
– maternal tissue provides nutrients– plants with embryos are called
embryophytes– embryo receives nutrition during
development from placental transfer cells
Multicellular,Dependent Embryos
Maternaltissue
Embryo
2 µm 10 µm
Wallingrowths
Placentaltransfercell (blue line)
Land plants: 4 characteristics
Walled SporesProduced in SporangiaLongitudinal section ofSphagnum sporangium (LM)
Spores
Sporangium
SporophyteGametophyte
Sporophyte and sporangiumof Sphagnum (a moss)
– 2. walled spores in sporangia• within the diploid sporophyte are multicellular organs called sporangia
(singular = sporangium) – production of haploid spores via meiosis• within a sporangium are diploid cells called sporocytes or spore mother
cells – undergo meiosis to generate the haploid spores of the sporangium
• the spores are protected by sporopellinin – key adaptation to terrestrial life
Land plants: 4 characteristics– 3. multicellular gametogangia
• the haploid gametophyte undergoes production of haploid gametes within multicellular gametogania (singular = gametoganium)
• the production of gametes is through mitotic division • female gametogania = archegonium - produces a single egg• male gametogania = antheridium – produces many flagellated sperm
Multicellular femaleGametangia
Archegonia and antheridiaof Marchantia (a liverwort)
Male gametophyte Antheridiumwith sperm
Female gametophyte
Archegoniumwith egg
Multicellular Male Gametangia
ApicalMeristemof shoot
Developingleaves
Shoot Root
– 4. apical meristems• light and CO2 are available above ground, water and minerals are
found mainly in the soil• must be a way of collecting these components• plants do this by growing in length – through the production of stems
and roots• these grow from stem cell-like tissues in the plant called meristems
Land plants: characteristics
ApicalMeristemof shoot
Developingleaves
Shoot Root
– 4. apical meristems• apical meristem – localized regions of cell division located at the tips of shoots
and roots• e.g. shoot apical meristem – cells divide by mitosis and cytokinesis to produce
progenitor cells for the rest of the stem• e.g. root apical meristem• progenitor cells from the meristem are the source for the tissues of the stem and
root
Land plants: characteristics
Plant Diversification• plant fossils dating back to 475 MYA• one major way to distinguish groups of plants is to classify them as: vascular & non-
vascular– vascular tissue – extensive system formed by cells joined into tubes– conduct water and nutrients– those without these tubes – non-vascular plants
• bryophytes: term used to refer to all non-vascular plants– do not form a monophyletic group or a single clade– known popularly as the mosses, liverworts and hornworts– is a debate as to how they are related to each other– don’t possess the advanced adaptations of vascular plants (e.g. roots & leaves)– they do share many characteristic with vascular plants – see the slide on 4 plant
characteristics• vascular plants: clade that includes 93% of all surviving plant species
– categorized into smaller clades:• 1. lycophytes – club mosses• 2. pteryophytes – ferns• 3. gymnosperms• 4. angiosperms
Ancestralgreen alga
Origin of land plants(about 475 mya)
Origin of vascular plants(about 420 mya)
Origin of seed plants(about 360 mya)
Land plants
Vascular plants
Seed plantsSeedless vascular plantsBryophytes
Live
rwor
ts
Hor
nwor
ts
Mos
ses
Lyco
phyt
es
Pter
ophy
tes
Gym
no-
sper
ms
Ang
io-
sper
ms
Cha
roph
ycea
ns
Non-vascular plants
• commonly known as the bryophytes– even though Bryophyta is one of the 3 phyla in
this group• three phyla:
– 1. Phylum Hepatophyta: liverworts• gametophytes are flattened into a thalloid
or a leafy shape• e.g. Marchantia
– 2. Phylum Anthocerophyta – hornworts• sporophyte can grow quite tall –
sporangium along the length– 3. Phylum Bryophyta – mosses
Marchantia polymorpha = liverwort
Plagiochila deltoidea = liverwort
Non-vascular plants
• two plant forms in the bryophyte life cycle– 1. Gametophyte– 2. Sporophyte
• sporophyte – bears spore-producing structures called sporangia (singular = sporangium)
• gametophyte – bears gamete-producing structures called gametangia (singular = gametangium)
• two kinds of gametangia– 1. Archegonium (female) – makes an egg– 2. Antheridium (male) – makes sperm
• moss life cycle is dominated by the gametophyte stage
Malegametophyte
“Bud” Spores develop intothreadlike protonemata.
Protonemata“Bud”
The haploid protonemata produce “buds” that grow into gametophytes.
Raindrop
Sperm
Antheridia
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.
Egg
Haploid (n)Diploid (2n)
Key
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.
Archegonia
Rhizoid
Femalegametophyte
GametophoreSpores
Sporangium
Peristome
MEIOSIS
Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.
FERTILIZATION(within archegonium)
Archegonium
Zygote
Embryo
Calyptra
Youngsporophyte
Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
The diploid zygote develops into a sporophyte embryo within the archegonium.
Capsule(sporangium)
Seta
Foot
Maturesporophytes
Capsule withperistome (SEM)
Femalegametophytes
Life Cycle of a Moss
http://www.sumanasinc.com/webcontent/animations/content/moss.html
Seedless Vascular Plants• bryophytes prominent during the first 100 million years of
plant evolution– but they are not very tall– rarely over 20 cm in height
• those plants that could achieve heights would have better access to sunlight, better spore dispersal
• height would mean the need for a transport system for water and nutrients
• would also need a structural support system• ferns are example of the evolution of plants that began to
develop height and a vascular system• fossils of present day vascular plants date back 425 MYA
Seedless Vascular Plants• 4 major characteristics of vascular plants:
– 1. dominant phase in the alternation of generations life cycle is the sporophyte
• the opposite case with bryophytes• e.g. ferns – the leafy plant is the sporophyte• the sporophyte becomes the larger and more complex stage of the life
cycle • dramatic reduction in gametophyte stage – may be under the soil• sporophyte no longer dependent on the gametophyte for nutrition
Seedless Vascular Plants• 4 major characteristics of vascular plants:
– 2. development of vascular tissues – xylem and phloem• xylem – conduction of water and minerals
– new cell population = tracheids – so vascular plants are often referred to as tracheophytes– water conducting cells contain a phenolic polymer – lignin–
• phloem – conduction of sugars and other nutrients– living cells– arranged into tubes for the distribution of sugars, amino acids and other
organic products
Seedless Vascular Plants• 4 major characteristics:
– 3. development of sporophylls: modified leaves that bear sporangia• two types: microphyll and megaphyll• e.g. in ferns – megaphylls with clusters of sporangia called sori• e.g. in lycophytes and gymnosperms – microphylls that form cone-like strobili
– most seedless vascular plants are homosporous – one type of sporangium that produces one type of spore
• this spore produces a bisexual gametophyte egg and sperm– heterosporous species has two types of sporangia that develop into two types of spores
• megasporangium - megaspore female gametophyte (egg)
• microsporangium - microspore male gametophyte (sperm) sperm
Seedless Vascular Plants• 4 major characteristics of vascular plants:
– 4. development of roots and leaves• rather than rhizoids – the sporophytes of vascular plants have evolved roots• roots – organs for the anchorage of the plant & absorption of water and nutrients
• leaves – organs for the increase of vascular surface area to capture more solar energy– megaphylls are larger and have a highly branched vascular system (of veins)
running through them» greater photosynthetic capacity
– microphylls are spine-like» supplied by a single, unbranched vein» appeared to have evolved first
Seedless Vascular plants• two divisions: Division Lycophyta and Division Pterophyta• ferns, horsetails and whisk ferns• the Pterophytes used to be divided by botanists into separate phyla:
• Phylum Sphenophyta – horsetails• Phylum Psilophyta – whisk ferns and relatives• Phylum Pterophyta – ferns
Equisetum – horsetail fern Psilotum – whisk fern
Phylum Lycophyta• club mosses, spike mosses and quillworts• 1200 species today• NOT true mosses since they have vascular tissue• most ancient line of vascular plants• modern lycophytes grow on tropical trees as
epiphytes – BUT they are NOT parasites
Diphasiastrum tristachyum, a club moss
Strobili(clusters ofsporangia)
epiphytic ferns
Phylum Lycophyta• microphyll line of evolution
– distinct line of evolution that came out of the first land plants– development of leaves from clusters of sporangia– earliest lycophytes formed primitive leaves = enations (now called
microphylls)– evolution of true roots – increased the size of the sporophyte– sporangia became clustered into compact cones or strobili– many species evolved heterospory
Phylum Pterophyta
• megaphyll line of evolution – development of leaves from a branching system of stems– seen in all seed vascular plants, ferns and arthrophytes (horsetails)– telome theory: main stem with dichotomously branching lateral stems– the lateral branches developed subdivisions – all on one plant– the last lateral branches = telomes– during evolution - tissue grew in between (webbing) – the telomes acquired spore-forming ability
telomes
Spore
Sperm
Antheridium
Egg
Haploid (n)Diploid (2n)
Key
Younggametophyte
Sorus
Sporangium
MEIOSIS
FERTILIZATION
Archegonium
ZygoteNewsporophyte
Maturesporophyte
Sporangium
Gametophyte
Fiddlehead
Fern Life Cycle
• in the sporophyte – presence of multiple sporangia clustered into a sorus (sori = plural)
• spores released from the sori and germination into a bisexual gametophyte• bisexual gametophyte develops male and female gametogania
– male antheridium – for sperm production– female archegonium - for egg development
• sperm are released and swim to the egg within the archegonium – fertilization and development into a diploid zygote
http://www.youtube.com/watch?v=9c9Zi3WFVRc
Spore
Sperm
Antheridium
Egg
Haploid (n)Diploid (2n)
Key
Younggametophyte
Sorus
Sporangium
MEIOSIS
FERTILIZATION
Archegonium
ZygoteNewsporophyte
Maturesporophyte
Sporangium
Gametophyte
Fiddlehead
Fern Life Cycle
• the zygote develops into a new diploid sporophyte – emerges from the gametophyte
• growth of the sporophyte produces fronds or megaphylls– young, developing frond is called the fiddlehead
• gametophyte disappears• fronds develop sporangia for the production of spores (via meiosis)• almost all fern species are homosporous
– produce one kind of spore bisexual gametophyte
• heterosporous fern species have megasporangium and microsporangium on the sporophyte – production of distinct spores for male and female gametophytes