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Biological Systems Module 4 (Plants (week 10) (Resource Acquisition &…
Biological Systems Module 4
Plants (week 9)
Plant Diversity
5 features
(differentiating from algae + reflecting adaptation)
5. Apical Meristems
allow plants to grow high above ground (CO2, light) and below ground (water, mineral nutrients)
specialised tissue at growing tips where rapid cell division occurs
Cells produced by apical meristem then differentiate into outer epidermis or other internal tissues
Protection
of gametes, zygotes, spores
2. Embryophytes
multicellular, dependent embyos
grow protected inside parent plant
4. Tough and protected spores
sporopollenin
makes walls more resistant to drying
sporangium
protective specialised organ where spores are produced
3. Gametangia
specialised organ for gamete production (sex organs)
Antheridium
(male)
Archegonium
(female)
1. Alternation of generations
switch between phases
sporophyte
multicellular diploid
gametophyte
multicellular haploid
Origin and Phylogeny of Land Plants
1.2 BYA
500 MYA
Now
290000 living species
small plants, fungi, animals emerged on land
Cyanobacteria appeared
Moving onto land
Advantages
More CO2 in air than water
Soil rich in mineral nutrients
bright sunlight, unfiltered by water
Less competition + predators
Disadvantages/Challenges
Scarcity of water
Lack of structural support against gravity
Closely related to green algae
classified as embryophytes by textbook
Plant Phyla
Non-vascular Plants
(Bryophytes)
(470MYA)
Mosses
Giant moss
Hornworts
Liverworts
Vascular Plants
(have vascular tissue)
(425 MYA)
Seedless vascular plants
Lycophytes
spike mosses
quilworts
club mosses
Monilophytes
ferns
horsetails
whisk ferns
Seed Plants
(flowering plants) (
360 MYA)
Gymnosperms
Angiosperms
Plant Classification
Kingdom: Plantae (land plants)
Plant characteristics
photosynthetic organisms
that have adapted to life on land
most live in terrestrial habitats
some returned to aquatic habitats e.g. seagrass
eukaryotes
cell walls
photosynthetic autotrophs
source of energy for metabolism = sunlight
fix CO2 to create organic compounds
live in terrestrial habitats (except extreme/harsh environments)
2 distinct forms
Nonvascular Plants (bryophytes)
Characteristics
primative land plants
simple
structure
need abundance of water/
moist
environments
lack specialised conductive tissues/no conducting system
usually quite
small
(some big)
3 Phyla
liverworts
(phylum Hepatophyta)
9000 species
usually small <2 cm
found in humid envrionments
hornworts
(phylum Anthocerophyta)
100 species
most small, grow in humid places
some larger, grow on trees
mosses
(phylum Bryophyta)
*note bryophytE= ALL nonvascular, bryophytA = ONLY mosses
15000 species
"carpet" is mostly
gametophytes
(dominant life stage)
Sporophytes are elongated, visible to the naked eye
Life Cycle
dominant gametophyte (haploid) stage
Spore
gametophyte
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(protonema + gametophore, anchored by rhizoid)
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Ecological Significance
colonise bare soil and rocks
help retain nitrogen
important role in creating niches for other organisms to live
peat bogs sore a lot of soil carbon (30%) yet only cover 3% of land surface
Higher temperatures causes peat moss to dry and decompose, releasing CO2
small herbaceous (nonwoody) plants
Life Cycle
(all 3 phyla)
gametophytes
larger and longer-living than sporophytes
sporophytes typically present only part of time
spore germinates into gametophytes
composed of
protonema
and gamete-producing
gametophore
rhizoids
anchor gametophytes to is constrained by lack of vascular tissues
the height of gametophyte is constrained by lack of vascular tissues
mature gametophytes produce
flagellated sperm
in antheridium and
egg
in archegonium
sperm swims through film of water to reach and fertilise egg
byophyte sporophyte
grow out of archegonium
smallest simplist sporophyte of all extant plant groups
Consists of
Seta
"stalk"
Sporangium
"capsule"
Foot
Each sporophyte releases enormous number of spores
1 moss capsule can generate over 5 million spores
Vascular Plants
Seedless vascular plants
2 Phyla
Phylum Monilophyta
(monilophytes)
e.g.
whisk ferns
horsetails
ferns
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most widespread seedless vascular plants (12000 species)
Phylum Lycophyta
(lycophytes)
e.g. (although not mosses)
quillworts
club mosses
spike mosses
most are herbaceous (small and not woody) now
In Carboniferous Period (359-299) there were 40m high trees
Ecological Importance
ancestors of lycophytes, horsetails, ferns grew tall in Devonian (419-359 MYA) and Carboniferous (359-299 MYA), forming
first forests
increased growth and photosynthesis removed from CO2, may have contributed to global cooling (at end of Carboniferous period)
decaying of these plants have become coal, which is being burnt and contributing to global warming
Life Cycle
still undergo alternation of generation
sporophyte phase greatly reduced
Characteristics
dominant sporophyte phase
transport in specialised
vascular tissues
xylem
dead tube-shaped cells "tracheids"
carries
water and minerals
up from roots
cell wall strengthened by
lignin
providing support and enabling greater height
phloem
living cells
distribute sugar, amino acids, organic products
Evolutionary advantage
structural support + ability to carry water and nutrients above ground
allows plants to grow taller
outcompete shorter plants for sunlight
disperse spores further (due to height)
well-developed
roots
and
leaves
Leaves
primary photosynthetic organ of vascular plants
greatly increases SA of vascular plants
can capture more sunlight energy for photosynthesis
Roots
anchors plant (like rhizoids)
absorbs water and nutrients form soil
Seed plants
Evolutionary innovation
gametophytes miniaturisation
dominant sporophyte phase
gametophyte dependent on sporophyte tissue for nutrition
heterospory
produces 2 kinds of spores
megaspore
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microspore
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Specialised structures to protect gametophyte
megaspore encased in
ovule
(protective and food layers)
megaspore gives rise to female gametophyte which stays sheltered in
ovule
when fertilised, ovule becomes
seed
microspore encased in pollen wall
contains sporopollenin (resistant to drying)
called
"pollen grain"
microspore gives rise to male gametophyte sheltered in pollen grain
Seeds and pollen grains
diploid sporophyte produces haploid spore (meiosis)
megaspore -> egg (within ovule)
microspore -> sperm (within pollen grain, generally without flagella)
only pollen grain leaves parent plant
pollination
pollen grain reaches and enters pollen tube of ovule
fertilisation
pollen nucleus reaches egg and and fuses -> seed
Internal fertilisation and protection of embryonic sporophyte (seed) distinguishes these plants -> adaptation to dry spells
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New sporophyte grows out of the seed
No independent gametophyte organism
1. Unfertilised ovule
2. fertilised ovule
3. gymnosperm seed
Phylogeny
2 sister clades
Gymnosperms
"gymno" = bare, naked "sperm" = seed
seeds exposed
dominant flora in Mesozoic (245-65 MYA)
4 extant phyla
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3 key features
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Life cycle
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Diversity
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Angiosperms
"angeion" = vessel, container "sperm" = seed
seeds contained in fruit
dominant flora in Cenozioc (40 MYA) particularly since late Eocene
1 phylum
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account for over 99.5% of all "higher plants" (seed plants) species
Key features
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Life Cycle
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Diversity
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Success
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Differences
wood structure
different pollen
gymnosperms lack flowers
number of phyla
Anatomy
Morphological development
reflects evolution
draw resources
above ground
CO2, light
below ground
water, minerals
2 systems
root system
below ground
shoot system
above ground
stems + leaves
vascular system distributes all the essential materials
3 plant tissue systems
Vascular
components
2 vascular tissues
phloem
transports
sugars
(products of photosynthesis) from leaves to where needed/stored (e.g. roots, site of growth, developing leaves, fruits etc.
alive cells
pores on sidewalls to connect cytoplasm with neighbouring cells
sieve tube
ends of phloem cells join to other cells
sieve plate
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transports sugars by active streaming of cytoplasm
companion cells
control activity
supporting cell
mature cells have no nucleus, associate with these cells
xylem
transports
water + dissolved
minerals
up from roots to shoots
dead (functioning) cell
water conductors (inc. dissolved minerals)
thick mutli-layered cell walls (strengthened with cellulose + lignin)
main cell type
tracheid
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vessel elements
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functions
carries out
long-distance transport
of materials between roots and shoots
components that conduct water, minerals, food (roots/shoots)
Ground
anything not vascular/dermal
woody part of plant
bulk of plant
functions
filler
storage
photosynthesis
support
short-distance transport
components
3 types of cells
Collenchyma
help support young parts of plant shoot
elongated cells, thicker cell wall, in strands/cylinders
provide flexible support without restricting growth
pliable but strong (cellulose + pectin)
alive, lose strength when dead
Sclerenchyma
support plant
thick cell wall, rich in lignin (extremely rigid like skeleton)
cannot elongate, occur in plants no longer growing
form sheets/strands in stems of plant, scattered amount other cells
many dead, thick cell wall remains as "skeleton" to support the organ (nonedible part)
Parenchyma
provide main soft tissue of stems, leaves, roots, petals
thin walls, massed together, perform several functions
photosynthesis in leaves
store starch in stem/roots
form basic structure for other cells
important for healing (first cells to grow during wound repair)
alive, fresh, cease functioning once dead
Dermal
components
epidermis
surface of plant covered in continuous layer of tightly packed cells
stem and leaves
protect against water loss
cuticle
special waxy coating (watertight surface)
roots
(water/mineral uptake)
leaves
stomata
increase gas exchange
composed of
2 guard cells
opens to let CO2 in, O2 out, H2O out
close when hot and dry to minimise H2O loss
functions
epidermis is barrier against disease-causing pathogens
enhance water and mineral uptake
prevent water loss
gas exchange
protective covering of plant (outside)
3 basic plant organs
Leaves
components
flattened blade
stalk/petiole
joins lead to node of stem
Types of leaves
complex
divided into
leaflets
(each may have own stalk)
simple
undivided blade
different
e.g. spines on cacti
veins
arrangement
eudicots
branching veins
monocots
parallel veins
functions
main photosynthetic organ of most vascular plants
intercept light (flat)
gas exchange (thin and flat)
dissipate heat by transpiration
leaf droppings
deciduous species
drop leaves all at one time in year
remain leafless for part of year
evergreen species
drop leaves at all times of year
not all at once
variations
spines
e.g. cacti spines
storage leaves
leaves store food
tendrils
forms coil to bring plant closer to supporter
carnivorous leaves
leaves produce exudate to attract and ensnare insects and dissolve insect with enzymes and absorb nutrients through leaf surface
Stems
components
plant organ bearing leaves and buds
alternating system of
nodes
points at which leaves are attached
internodes
stem segments between nodes
apical bud
shoot tip where where most growth in young shoot occurs
auxiliary bud
structure that has potential to form lateral shoot/branch
apical dominance allows maintain dormancy in most auxiliary buds
sends chemicals to prevent other buds from growing too quickly
functions
elongate and orient shoot
maximise photosynthesis in leaves
allow growth/height
elevate reproductive structures
maximise dispersal
green stems also perform limited amount of
photosynthesis
variations
stolons
horizontal shoots that grow alone surface aka "runners"
tubers
e.g. potatoes, enlarged ends of rhizomes/stolons specialised for food storage
rhizomes
horizontal shoot that grows below surface, vertical shoots emerge from axillary buds
Roots
components
most eudicots/gymnosperms
taproot system
taproot
primary root
1st root to emerge from germinating seed
lateral roots
branch roots
arise from taproot
increase SA/absorption
most monocots
fibrous root system
primary root dies early on
adventitious roots
small roots arise from stems or leaves
lateral roots
roots arise from adventitious roots
good for preventing soil erosion
most plants
tips of elongating roots
absorption occurs
many
tiny root hairs
(increase SA)
mycorrhizal associations
mutualistic relationship with fungi
dramatically increases SA
plant -> sugar, fungi -> nutrients
some plants
specialised roots
prop roots
"strangling" aerial roots
storage roots
buttress roots
pneumatophores
like snorkels for gas exchange
functions
anchors
plant
absorbs
minerals
+
water
stores
carbohydrates
+ other
reserves
Plants (week 10)
Resource Acquisition & Transport in Vascular Plants
short range transport
cell-to-cell transport at tissue level
3 routes
Symplastic
via cytosol of cell
requires entry into 1 cell, then moves via plasmodesmata
transmembrane
between cells across cell membrane (repeated crossing)
enter and exit back and forth
Apoplastic
external to cell membrane
everything outside cell membrane within cell wall
Controlled by
selective cell membrane permeability
active and passive transport
H+ gradient
membrane potential established through pumping H+ by proton pumps
energy of H+ gradients used to co transport other solutes by active transport e.g. sucrose
Water
absorption or loss occurs via osmosis
diffusion of free water across channels in plasma membrane called aquaporin channels
water potential
determines likelihood of water movement
units: megapascals (MPa)
sum of
solute potential
and
pressure potential
solute potential is proportional to solute concentration (always negative e.g. more concentrated, more negative)
pressure potential is physical pressure (push/pull) of solution
water moves from
high to lower
water potential
Turgor pressure
pressure put on cell wall by protoplast (living part of cell i.e. everything in cell membrane) from swelling caused by water
affected by amount of water already inside of cell
Turgid
when cell taken up maximum amount of water, cell wall exerts pressure back on protoplast
Flaccid
equilibrium between water uptake and loss
Plasmolysed
when cell has lost so much water, plasma membrane is no longer connected to cell wall
Effect of turgor loss
hyperosmotic
walled cell with greater solute concentration than surroundings
becomes turgid i.e. very firm
nonwoody tissue pushes against each other
stiffening of tissues
iso/hypo-osmotic
flaccid
turgor loss
causes wilting
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water and nutrient uptake in roots
water and dissolved minerals enter root via root hair
apoplastic route
passive diffusion into hydrophilic cell wall
water moves along exterior to plasma membrane
symplastic route
active uptake into cells
passes through endoderm
reaches vascular cylinder
Casparian strip
prevents passage via cell wall (apoplastic)
forces to pass through cell membrane at least once before reaching vascular system
keeps many toxic substances out
long distance transport
transport of sap in xylem and phloem in vascular system at "whole" plant level
occurs by
bulk flow
in pipe systems
in tracheids (and vessel elements) of
xylem
for water and nutrients
dead cell
no cytoplasm
only cell wall -> "pipes"
in seive-tube elements of
phloem
for sugars and organic compounds
almost devoid of organelles -> "pipes"
companion cells
Phloem
pushing phloem sap
pressure-flow hypothesis
in angiosperms, phloem sap flows in sieve-tube elements
contains up to 30% sucrose + amino acids, hormones, minerals
minerals contribute to pushing of sap
flows from site of sugar production to sugar use/storage
sugar source -> sugar sink
e.g. growing roots, stems, fruit
moves by
active transport
(positive pressure) bulk flow
runs in both directions
transports
chemical messengers (hormones)
integral for synchronising processes in plants
viruses
macromolecules e.g. proteins, RNA
small organic molecules e.g. sugars, amino acids
systemic transport (throughout the body)
critical to integrate all functions of the plant
Xylem
pulling xylem sap
cohesion tension hypothesis
depends on
transpiration
at leaves
physical cohesion
of water molecules
water molecules lost by
evaporation
at stomata
water loss induces
negative pressure potential
(due : to high surface tension of water)
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water regulation (via stomata)
rate of transpiration regulated by stomata
stomata
generally on underside of leaf
regulates CO2, O2 gas exchange
usually open during day when carbon dioxide is required for photosynthesis
generally closed at night to stop loss of water
exceptions: C3/C4/CAM adaptations
evolution
algal plant ancestors
no complex vascular system
ocean provided buoyancy and ample water
bryophytes (first land plants)
lacked vascular systems
require intimate contact with water
moist environments
vascular plants
conducting tissues
allow true tissue differentiation
roots absorb water and minerals from soil and distribute to rest of plant via vascular tissue
shoot system harvests sun energy and atmospheric CO2 for photosynthesis
favourable adaptations (benefits and costs)
taller plants
requires more anchorage
leaves with larger surface area
more evaporation
more need for water
outcompetes other plants for light, water, nutrients
multicellular, branching roots
more efficient long distance transport system between roots to leaves
Soil & Plant Nutrients
Soil
Texture
soil horizons
(stratified into layers)
B horizon
contains less organic matter and is less weathered
C horizon
composed of partially broken-down rocks
A horizon
"topsoil"
consists of
living organisms
mineral particles
humus
(decaying organic material)
very important
Determinants of texture
size of inorganic soil particles
affect soil characteristics
soil is usually a mix of sand, clay and silt
loams
most fertile topsoils
contain equal amounts of sand, silt, clay
good balance between aeration, drainage and water storage capacity
sand
largest particles (0.5-2mm)
larger spaces b/w particulaes
well oxygenated
does not retain water
good for giving drainage
clay soil
small particles (<0.002mm)
particles tightly packed
poor oxygen
good water retention
negatively charged
high attraction to polar water
silt
in between
0.002-0.05 mm
Water in soil
soil solution consists off
water and dissolved minerals in pores between soil particles
after heavy rainfall
water drains from large spaces in soil
small spaces retain water because it is attracted to negatively charged surfaces of clay and other particles
film of loosely bound water is available to plants
Components
contains living, complex ecosystem
living organisms play important rile in soil layers
Composition
inorganic (mineral)
clay particles are
anions
some nutrients are anions e,g. phosphate H2PO4^-, nitrate NO3^-, sulphate SO4^2-
cannot bind to soil particles and are lost by
leaching
when water percolates soil
cations e.g. Ca2+, K_, Mg2+
adhere to negatively charged soil particles
prevents them from leaching out
may not be available to plants to uptake due to binding to soil
cation exchange
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organic
humus
dead organic material from fallen leaves, dead organisms, faeces, organic material from bacteria, fungi
builds crumbly soil that retains water but still porous
increases soil's capacity to exchange cations and serves as reservoir of mineral nutrients
topsoil contains
bacteria, fungi, algae, other protists, insects, earthworms, nematodes, plant roots
helo to decompose organic material and mix the soil
full of life
insects, soil fungi, earthworms, soil protozoans, nematodes, pseudoscorpion, slug, termite, cockroach, beatle, ant, millipede, cicada nymph, slater etc.
important for recycling nutrients
Australian soil
heavily leached
low levels of nutrients
land use
farming and grazing have worsened soil conditions
influences structure, nutrient, status, salinity of soils
significant environmental impact
grazing and tilling broke up delicate mat of algae and lichen that held topsoil together
not much A or B horizon
not much humus in soils
14 different classes of soils in Australia
most common soils in Qld
vertosols
abundant clay texture
floodplains
shrink and crack when dry
expand when wet
kandosols
rich in quartz
little texture
weak B horizon
abundant clay texture
erosion
thousands of acres of farmland lost to water/wind erosion every year
causes loss of nutrients
salinisation
due to replacement of deep-rooted native plants with shallow-rooted crops
low water table
less evaporation
salt comes up and accumulates
loss of nutrients
loss of wildlife
Soil Conservation
Solutions to damaged soil
salinsation
drip irrigation
requires less water and reduces salinsation
fertilisation
soil can be depleted of nutrients as plants are harvested
fertilisation replaced mineral nutrients that have been lost
commercial fertilisers have N, P, K
excess can cause leaching and cause algal blooms (eutrophication)
organic fertilisers
composed of manure, fishmeal, compost
release N, P, K slowly as they decompose
better for environment
erosion
topsoil lost to water and wind erosion
causes loss of nutrients
reduced by
planting trees
windbreaker
root stabilisation
terracing hillside crops
cultivating in a contour pattern
no-till agriculture
growing crops year to year w/o disturbing soil through tillage
completely eliminates soil erosion
soil management by fertilisation and other practices helped establish modern societies
allowed settlement
irrigation
requires high volumes of water
drains water resources
75% of global freshwater used for agriculture
agriculture = 62% of water consumption
can lead to
land subsidence
primary source of irrigation water = aquifers
underground water reserves
depletion of aquifers causes land subsidence
sinking/settling of land
can lead to
salinisation
concentration of salts in soil as water evaporates
soil pH
affects cation exchange and chemical form of minerals
cations are more available in slightly acidic soil as H+ displace mineral cations from clay
availability of different minerals varies with pH
e.g. pH 8 plants can absorb calcium but not iron
Nutrient needs
obtained by plants mostly through upper layers of soil
for growth and reproduction, plants need
water
from the ground
air
CO2
Oxygen
Nitrogen (N-fixing symbiont)
soil
minerals and nutrients
macronutrients
essential elements needed in LARGE quantities
major components of organic compounds that form plant structure
C, H, O, N, S
nitrogen
nitrogen contributes most to plant growth/crop yield
required for proteins, nucleic acids, chlorophyll, other important organic compounds
inorganic catalysts
needed to facilitate biochemical reactions (enzymes, coenzymes)
e.g. Ca2+, K+, Mg2+
micronutrients
essential elements needed in SMALL quantities
e.g. chlorine, iron, manganese, boron, zinc, copper, nickel, molybdenum
often act as cofactors
nonprotein helpers in enzymatic reactions
Deficiency Symptoms
depend on mineral's function
macronutrient deficiency more common
e.g. wilting, yellowing of leaves etc.
Soil benefits
nutrient absorption
anchorage and stability
enables tall growth
withstand wind, storms etc. w/o falling
mutualistic symbionts
bacteria and fungi
mineral nutrients
fixed nitrogen
some fungi
mychorrizal associations
increase SA
greater absorption of nutrients (water and minerals)
Mutualistic relationships
relationship between plants and microorganisms
plants provide photosynthetic products for energy and as a carbon source
microorganism provides mineral nutrients and fixed nitrogen
fungi and plant
mycorrhizae
mutualistic associations of fungi and roots
fungus gains stead supply of sugar from host plant
increases SA for water uptake and mineral absorption
mycorrhizal fungi secrete growth factors
stimulates root growth and branching
bacteria in root nodules
help legumes by fixing nitrogen
bacteria gain place to live and food (sugars)
Plant Growth & Development
Organisation of tissues in roots, stems, leaves
Roots
Structure
Cortex
ground tissue (mostly parenchyma cells)
air space between cells
allows easy flow of water/nutrients
vascular cylinders
solid core of xylem and phloem
surrounded by
root endodermis
layer of cell between ground tissue
forms a barrier to regulate passage of substrates from soil to vascular tissue
Root epidermis
absorptive portion of root (not waxy cuticle)
single layer of cells
includes root hairs (70-90% of SA)
increases water uptake
Root cap
dome shaped cell mass
Protects root/apical meristems as it pushes through soil
Organisation of tissues
different arrangement of vascular tissues
eudicots
(and conifers)
star shape xylem
monocots
ring of xylem alternating in phloem
Stems
structure
Epidermis
waxy cuticle
single layer
ground tissues
mostly parenchyma
some collenchyma for support in growing tips
schlerenchyma in older tissue
vascular tissue
runs length of stem in groups (
vascular bundles)
bundles converge into cylinder of root
have primary xylem and phloem
xylem is closer to centre of stem
near soil surface
Organisation of tissues
different arrangement of vascular tissues
eudicots
(and conifers)
vascular bundles form ring around stem
organised
monocots
distributed throughout ground tissue
spaced out randomly
Leaf
Structure
dermal
epidermal cell
upper epidermis
guard cells
lower epidermis
ground
palisade mesophyll
spongy mesopyll
bundle-sheath cell
vascular
xylem
phloem
vein
Function
2 types of plant growth
primary
extends/elongates the tips of shoot and roots (
lengthwise
)
apical meristems
produce
primary tissues
2. ground meristem
ground tissue
3. procambium
vascular tissue
1. protoderm
dermal tissue
early differentiating tissues
rapidly dividing tissues which is the origin of all tissues
initially 2 meristems in embryo (roots/shoots)
all meristems at the end of roots/branches
replaces epidermis
axillary bud meristem
contains primary phloem and xylem
Occurs in
annual plants
most monocots
woody plants (only recently formed part of plant is primary growth)
Growth in roots
root tip covered by
root cap
protects apical meristem as root pushes through soil
growth occurs just behind the root tip
three zones of cells
zone of
elongation
where new cells elongate (up to 10x length)
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zone of
differentiation
aka maturation
cells complete differentiation becoming distinct cell types/tissues
zone of
cell division
stem cells and immediate products
Lateral growth in roots
if resource rich pocket detected in surrounding soil
stimulates branching of roots (busts/rips out)
pushes through outer tissues until emerge from established root
lateral roots arise from stem cells on edge of vascular cylinder
develop into lateral roots (secondary)
Growth in shoots
apical meristem in shot protected by leaves of apical bud
apical meristem gives rise to
protoderm
dermal
ground meristem
ground tissue
procambium
vascular tissue
structurally different but same differentiation
leaf primordial has all makings of leaves
Lateral growth in shoots
axillary buds have meristems
apical dominance
axillary meristems chemically suppressed by plant hormone released by nearby apical meristem
prevents excessive branching
apical bud chemically asserts dominance
if apical meristem removed (or far enough)
axillary bud breaks dormancy and develops into lateral shot/branch
secondary
thickens
parts produced in previous years (becoming more robust)
lateral meristems
2 types
cork cambium
produces touch, thick covering of waxy cells (bark)
adds secondary dermal tissue
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bark protects tree
periderm
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bark
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vascular cambium
adds
secondary xylem
(wood)
inside
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increases vascular flow and suppor for shoots
produces
phloem
(secondary tissue)
outside
vascular and cork cambium are "cylinders" of dividing cells (one cell thick) within root/stem
occur in plants with secondary growth
Occurs in
gymnosperms
any eudicots
unusual in monocots
stems and roots of woody plants (in sites other than tips of roots/stems)
appears in angiosperms
most trees
adding diameter to stems/branches on annual/continual basis
Meristematic origins
indeterminate growth
growth occurs throughout a plant's life
plant has embryonic, developing and mature organs all at the same time
Growth occurs from
meristems
undifferentiated tissues
similar to stem cells, which gives rise to different tissue types
Life span
Annuals
complete life cycle in <1 year
germination -> flowering -> seed production -> death)
e.g. wildflowers, staple food crops (wheat, rice, legumes)
Don't need secondary growth
Biennials
2 growing seasons to complete life cycle
e.g. carrot, turnip
flowers often produced in second growing season
Perennials
live many years
don't die of old age
death usually caused by disease or environmental trauma (fire, drought)
e.g. trees, grasses
relationship with primary growth
in woody plants primary and secondary growth occurs simultaneously
primary
adds leaves
lengthens stems and roots
comes from apical meristem
secondary
increases diameter in older regions of stems and roots
older tissues
meristematic potential
Summary of primary and secondary growth
apical meristem of stem
primary meristems
protoderm
procambium
ground meristem
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primary phloem
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primary xylem
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vascular cambium
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epidermis
primary tissues
lateral meristems
secondary tissues
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Plants (week 11)
Plant-Animal Interactions
Types of Interactions
mutualistic (+/+)
ants and
Acacia
(ants serve as bodyguards, clear out nearby plants)
edible seeds eaten (and defecated) by animals
pollination (plants get pollinated, animals get nectar)
commensal (+/0)
animals
bird nesting, shelter
plants
seed hitch-hiking on animals (esp. fur ones)
antagonistic (+/-)
animals
direct consumption of plant for food
plants
carnivorous plants, bee orchid (trick bees by visual/chemical mimicry (female pheromone) into mating with flower
Relationship to pollinator
pollination
pollen (male gamete) is transferred to female reproductive organ of plant -> fertilisation
gymnosperms rely on abiotic dispersal e.g. wind (affected by chance and high % of loss)
angiosperms rely on animals to transfer pollen from anther of 1 flower to stimga of other flower
animal pollinators
65% of flowering plants use insects e.g. bees, flies, moths, butterflies
bees
attracted to bright colours (yellow, blue)
80% of commercial crops pollinated by bees
see UV radiation -> many flowers have UV markings/nectar guides
honey
foraging bee stores nectar in special stomach
returns to hives and passes by mouth to indoor bee
stored into specialised storage cells (honeycomb)
moisture content decreased by wind fanning/evaporation
once thickened, honey capped with beeswax
pollen mixed in to make bee bread, fed to larvae
CCD (colony collapse disorder)
since mid-200s
neonicotinoid insecticides
chemical stress, reduce reproduction and life span
parasites more likely to affect stressed individuals
colonies with inexperienced young males less likely to thrive
flies
flowers-reddish, fleshy, odour like rotten meat
flies lay eggs which day after they hatch due to no food
limited benefit for flies (flies may harvest chemical scents, which are used for male pheromone reproduction)
moths and butterflies
detect odours
flowers-sweet fragrance and colourful (white, yellow)
other pollinators are birds, mammals
birds
low sense of smell
flowers- large, bright red/yellow, little odour
flowers product highly sugary nectar (to meet energy requirements of birds)
mammals
bats, non-flying mammals
flowers- light-coloured, aromatic to attract nocturnal pollinators
reward is
nectar
specialised sugar-rich liquid produced in nectarines (specialised glands)
floral nectarines
produced in flowers to reward pollinators
extrafloral nectarines
produced elsewhere (e.g.base of leaves) to reward bodyguards (e.g. ants, wasps)
Co-evolution
natural selection favours deviation in floral structure that increase likelihood of pollination by pollinator
large diversity in insects is linked to large diversity in floral morphology and physiology of angiosperms
e.g. Madagascar orchid and hawk moth
Plant Defences
Threats
herbivorous animals
parasitic fungi
bacteria
viruses
Types of Defences
Chemical
plants produce toxic chemicals/poisons
nicotine (toxic to insects)
Digoxin (used for heart med)
toxic alkaaloids (morphine, strychnine, coniine (hemlcok))
phytoecdysteroids
chemicals that mimic moulting hormones
interfere with insect moulting
clover disease
chemicals in clover mimic phytoestrogen
potent animal female hormone
causes infertility in sheep
volatile alarm chemicals
released when injured
alert nearby plants of danger
attract carnivorous insects (bodyguards)
attract insectivorous birds
attract ants
to serve as standing army against herbivores
by providing food
Biological
biological warfare
silencing RNA
silence RNA of pathogens using small interfering RNA molecules
target genes for growth/development and survival
holds potential for crop protection
mimicry
look uninviting
appear partially eaten
appear to have eggs (dissuading egg laying insects)
mimic carnivorous insect
immune system
Physical
first line of defense
macroscopic level
waxy cuticle
epidermis
periderm
large spines or thorns
large herbivores
fine hair spine ("trichomes")
herbivorous insects
some trichomes produce toxic chemicals cocktails (e.g. azadirachtin, pyrethrum)
barriers can be breached (damage from grazing herbivores)
microbes can also gain entry at open stomata
microscopic level
tough cells (plant cell wall, sclerenchyma cells)
difficult to eat
silica used to create "plant stones" ("plytoliths")
really difficult to eat (reduces growth rate of herbivorous insects, abrades teeth)
Behavioural responses
wild tobacco
response to herbivory
releases nicotine (neurotoxicant) when fed upon
some caterpillars immune
plant releases volatile chemical messenger attracting insect mercenaries that eat caterpillars
evil lollipop
sugar attracts caterpillars, which causes them to smell, attracting predators
to many caterpillars still
change flowering time
bloom during the day instead of at night
Typical immune. response
2 types
Effector-triggered immunity
some bacteria have effectors (chemicals) to suppress PAMP response
hypersensitive response
kills plant tissue at site of infection
systematic acquired resistance (call to arms)
infection site produces
alarm chemical
(salicylic acid from methyl salicylate), which induces plant wide expression of
defense genes
PAMP-triggered immunity
"pathogen associated molecular pattern"
based on detection of non-plant molecules
plant detects alien molecule -> produce broad-spectrum antimicrobial chemicals with fungicidal/bactericidal properties
Plant Behaviour
Behaviour (definition)
Examples
Plants
Detection of
photoreceptors (detect light)
mechanical stimulation (wind, herbivory, physical environment e.g. support structures)
physical environment (gravity, temperature, soil water salt, CO2)
gravity
shoots grow upwards, roots grow downwards even int eh absence of light because plants can detect gravity
statoliths
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chemical receptors (nutrients, scents e.g. dodder vine can detect tomato smell)
respond with growth
moves in response to environmental information
stem and leaves towards the sun
foraging roots towards nutrients in the ground
root elongation slows down and root hairs spread out in areas of high nutrients
slow, so we generally don't see it but slow down
Animals
respond with movements
reactions are faster
the way that an organism responds to an external stimulus
Plant Hormones
regulate virtually all aspects of growth and development
plant hormones can have different effects in different tissues and the development stage of the plant
multiple hormones often interact to control growth and development
Signal transduction
reception
transduction
Response
Examples
Auxin
chemical messenger produced mainly by shoot, involved in
cell elongation (increases cell size)
stem elongation
enhances apical dominance
formation of lateral and adventitious roots
regulates development of fruit
phototropism (response to light)
gravitropism (response to gravity)
synthetic auxins
useful in vegetative propagation of plants by cutting (stimulates formation of adventitious roots)
monocots can rapidly degrade auxins but eudicots cannot (application of synthetic auxins (e.g. herbicide 2, 4D) kills eudicots by hormonal overdose)
Cytokinins
chemical messenger produced mainly in roots
cell division (thus works in concert with auxin for elongation)
antagonises the apical dominance action of auxin
Giberellins
involved in stem elongation
with auxin, involved in fruit development
use synthetic gibberellin sprays to make fruit bigger
when combined with water, triggers seed germination
Ethylene (gas)
tip of growing seedling meets obstacle, ethylene is produced "triple response" (enables the shoot avoid obstacle)
slows stem elongation
thickens/strengthens stem
curvature (causes the stem to grow horizontally)
responsible for
lead abscission (loss of leaves from deciduous trees)
fruit ripening (initiates enzymatic breakdown of cell wall and conversion of acids and starches to sugars to make the fruit sweet attract animals
commonly used in commercial fruit production
senescence (programmed cell death)
All living organisms must be able to
organise biological molecules on higher level
access and use energy
grow
reproduce
respond to environment
Response to Light
light
important factor for photosynthesis
triggers key events in plant development/photomorphogenesis
allows plants to measure the passage of days/seasons
plants use changing of day length (
photoperiod
) over a year to adapt to different seasons
e.g. to avoid producing leaves in winter (for deciduous trees)
photoperiod is critical for determining when
flowering
occurs
ensure flowers are produced when the right pollinators are present
long-day plants
spinach, lettuce, irises
flower only when photoperiod is more than 14h i.e. spring/summer
short-day plants
chrysanthenums, soybeans
flower only when the photoperiod is less than a specific number of hours i.e. in autumn/winter
measure is highly accurate
controlled by length of darkness rather than day length
plants detect
presence/absence of light
direction
intensity
wavelength (particularly red and blue)
blue light receptors
blue light initiates range of responses
phototropism
(growth towards light)
light-induced
opening of stomata
light-induced slowing of elongation of juvenile shoot (
hypocotyl
) after is breaks ground
red light receptors
red light measures light quality and competition
far red
(740nm
NOT absorbed
by overhanging leaves) to
red
(660nm
absorbed
by overhanging leaves)
phytochrome change shape depending on the presence of red, far red or no light
responses to red light
seed germination
seeds have limited food reserves, many seeds germinate only if light environment and other conditions are optimal e.g. death of a shading tree
shade avoidance
stimulates branching, inhibits vertical growth
setting of
internal clock
biological clocks
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flowering
environmental stresses
biotic
living e.g. herbivores
abiotic
non-living e.g. water, temperature
water stress
drought
water needed for photosynthesis
water deficit
stomata closes
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other responses include
grass roll into tubelike shape to reduce exposure to dry air
shed leaves
consequences of response
reduced photosythesis
enables plant to survive
flooding
flooded soils have no air space
less O2 available for cell resp.
adapted specialised aerial roots (e.g. mangroves)
some produce ethylene in response to flooding, which kills some cells in the root cortex, creating an air tube (=snorkel)
salt stresses
2 salt impacts
excess soil sodium decreases water potential of the soil, thus causing a deficit in net movement of water to the plant
sodium is toxic to plants at high concentrations
some plants can produce organic compounds to counteract these negative effects (to a certain extent)
temperature stresses
heat
heat denatures proteins
transpiration cools down plants (via evaporative cooling)
plants close stomata in dry conditions to stop cooling -> synthesize heat-shock proteins which acts as scaffolds around proteins to help maintain their shape
cold
plants in cold climates also secrete extra sugar to protects against frost
decreases membrane fluidity, alternating transport across the cell membrane -> plants increase proportion of
unsaturated fat
in membrane when exposed to low temps (which helps maintain fluidity)
mechanical stimulation
plants respond to touch
plants that are touched grow more slowly
vines coil rapidly around support, to climb upwards towards a forest canopy
most plant responses are mediated by
hormones
(chemical messengers of the endocrine system), but a few are similar to an action potential in the nervous system e.g. rapid leaf folding in response to touch in
Mimosa pudica
Plant Intelligence
define intelligence
"sensory perception, information processing, learning, memory, choice, optimisation of resource sequestration with minimal outlay, self-recognition, and foresight by predictive modellling"
"a capacity for problem solving in recurrent and novel situations"
plants may not have a brain, but they exhibit behaviour, and even intelligence
plants communicate actively with other lifeforms
other plants
competition
push and shove towards sun
release toxins and conduct chemical warfare underground
compete for sunlight and nutrients
collaborate
reduce root growth when near siblings to reduce competition
in forests, trees connected underground by huge mycorrhizal network
trees can share carbon with fungi and each other
recognise relatives (via chemical signatures)
animals (e.g. plants attacked by herbivorous insects release "help" chemicals that attract carnivorous insects)
Plants (week 12)
Principles of Ecology
Factors
Biotic
(living)
different species and interactions
resources (necessary for survival, reduced when used)
Abiotic
(non-living)
climate (temperature, precipitation, sunlight)
geochemistry (soil, salinity, nutrients, pH)
determine types of ecosystems that are possible (i.e. based on rain, nutrient availability)
species distributions
dispersal
natural range expansion and adaptive radiation
anthropogenic (caused by humans) e.g. species transplant
biotic
presence of other species e.g. predators, herbivores
abiotic
temperature, fire, water, oxygen, salinity, sunlight, rocks, soil
Types of species interaction
Antagonistic (+/-)
predation
(predator kills/eats prey)
herbivory
(herbivore eats parts of plant/alga)
Parasitism
(parasite gains nourishment form host, which is harmed in process e.g. wasp laying eggs)
Mutualistic (+/+)
beneficial to both organisms (N-fixing bacteria and plant root, cellulose digestion in termite gut, photosynthetic algae in coral)
Competitive (-/-)
different species compete for resources that limit survival
Amensalism (0/-)
no effect on initiator, negative effect on recipient
Commensalism (+/0)
positive effect on initiator, no effect on recipient
Energy flow
all energy comes from sunlight (photosynthesis)
deforestation reduces planetary assimilation of energy
production efficiency
energy lost with each step of food chain
Biomes
Terrestrial
(mostly determined by
rainfall
and
temp
)
high rainfall (forest)
tropical rainforest
(always hot, high rain)
tropical dry forest
(always hot, season high rain)
temperate forest
(variable temp, seasonal high rain)
northern coniferous forest
(cold, season high rain)
moderate rainfall (grassland)
savanna
(always warm, season mod. rain)
chaparral/shrubland
(vary temp, season mod rain)
temperate grassland
(vary temp, season rain)
tundra
(cold, season rain)
low rainfall (desert)
Aquatic
(mostly determined by
salinity
-fresh v marine,
light
(photic zone at top, aphotic zone below),
water
(pelagic zone)/
sediment
(benthic zone)
brackish
estuaries
saltwater
intertidal zones
ocean pelagic zone
coral reefs
marine benthic zone
freshwater
lakes
wetlands
streams and rivers
biosphere
global ecosystem
Factors which determine biome
Climate
precipitation
sunlight
wind
temperature
Global air circulation
intense solar radiation at equator creates air circulation cells (wet at 0 and 60 degrees, dry at 30 and 90 degrees)
axial tilt
seasons
wind
ocena currents
geography
rainfall
Ecology
Definition: study of how organisms interact with members of same species (population ecology), members of different species (community ecology) and with their environment
Hierarchy
1. Individual
(organism born, grows, dies)
2. Population
(group of organisms in same species in same area)
3, Community
(different populations of species living in same area, may/may not interact)
4. Ecosystem
(combination of community of species (biotic) and abiotic environment
Human Impact
Direct
habitat degradation
deforestation, soil erosion, desertification
due to agriculture, industry, construction e.g. Murray-Darlin Basin
species transplatt
introduction of invasive species
e.g. cane toad, rabbit, fox, camel, myna, mosquitofish, trout, black-striped mussel, weeds in Aus
over-harvesting
e.g. fishing
Indirect
pollution
toxic antropogenic polutants
e.g pesticides (intentional)
e.g. PCBs, dioxins, heavy metals etc. (unintentional)
gross pollutants
plastics (leach toxic compounds into ocean gyres, slow break down, animal ingestion, toxic pills-bioaccumulators)
disruption of geochemical element cycles
N, P, C
Nitrogen
nitrogen is limiting nutrient for plant growth
intensive use of N in form of ammonia in fertilisers increase reactive nitrogen
eutrophication
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Carbon
carbon removed from reservoirs and released into atmosphere (deforestation, fossil fuel burning)
destruction of forest habitats
increased CO2 in atmosphere
changing relative abundancy
Climate Change
Consequences
melting ice caps and glaciers
sea level rise
increase heat in atmosphere
more energy
more intense weather events
shifting biomes
must adapt to change
ocean acidification
More CO2 in water, more H+ ions
big impact on survival of shell forming organisms and marine animals that regulate pH
Causes
human activities (fossil fuel, industry, agriculture)
release GHG (CO2, CH4, N2O), increasing GH effect
global rise in temperature, ocean acdification
Implications on human population growth
temperature predictions- 1/5th of humanity will be at risk by 2100 - deadly humidity levels that human body cannot handle
exponential growth over past centuries (aided by technology and medicine in industrial revolution, plagues, wars etc. only minimally influenced)
estimated to top 8 bill. by 2025 or sooner
growth rate (r) = birth rate - death rate
if b > d, r increases
if r < d, r decreases
growth is not sustainable
Thomas MaltusPaul Ehrlich
population limited by food availability
limited by food shortages, irreparable environmental damage
carrying capacity (K)
capacity of environment to sustain a population indefinitely without destroying that environment (logistic model)
collapse of civilisations
more humans=more environmental damage (pollution, habitat destruction, GHG)
2 main factors that predict sustainability/collapse of societies
ecological strain
depletion of natural resources, climate change
social strain
external (hostile neighbours/ trade partners)
internal (social inequalities)
Gini coefficient/index
measure of wealth inequality
0= perfect equality
100= max. inequality
Steps to avoid civilisation collapse
(address social and environmental issues)
reduce social inequalities
tackle climate change now
reconnect humans with nature (growing urbanisation)
manage human development to minimise/eliminate negative environmental impact
leadership
