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(Plants (week 10)) - Coggle Diagram
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 support 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
many 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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