enriched bio Flashcards
outcome of bonsai experiment
fertilization did not increase the growth rate of the small trees
they didnt exhibit a dwarf phenotype due to nutrient deprivation
might be the small root structure
explain the two worlds land plants live in
above ground = shoot systems acquire sunlight and co2
below ground = root systems acquire water and minerals
what did algal ancestors of plants absorb
water, minerals and co2 from the water they lived in
what did earliest land plants have
nonvascular plants that grew photosynthetic shoots above the shallow water
leafless shoots had waxy cuticles and few stomata = allowed them to avoid excess water loss and permits some exchange of co2 and o2
early land plants anchoring and absorbing functions were assumed by
base of the stem or by threadlike rhizoids
land plants evolved and increased in number lead to
competition for light water and nutrients
evolution of vascular tissues like xylem and phloem lead to
made possible the development of extensive roots and shoots systems that carry out long distance transport
what does xylem do
transports water and minerals from roots to shoots
what does phloem do
transports products of photosynthesis from where they are made or stores to where they need to be
describe the plants that had an advantage in absorbing light
taller plants with broad flat appendages
describe the plants that need more water
increased surface area (broad, flat appendages) lead to more evaporation
describe the plants that require more anchorage
larger shoots
what did greater shoot heights do
further separated the top of photosynthetic shoots from the nonphotosynthetic parts below ground
what did natural selection favour
plants capable of efficient long distance transport of water minerals and products of photosynthesis
what do the adaptations have to do
compromise between enhancing photosynthesis and minimizing water loss
diversity in plants is due to
differences in branching patterns, dimensions, shapes, and orientations of the shoot’s two components
name the shoots two components
stems and leaves
what does shoot architecture facilitate
light capture for photosynthesis
what do stems do
supporting structures for leaves
conduits for the transport of water and nutrients
name the two architectural features affecting light capture
branching pattern and length of stems
describe tall plants
thick stems, greater vascular flow, stronger mechanical support
describe vines
rely on other objects to support their stem
describe woody plants
stems become thicker through secondary growth
branching enables
plants to harvest sunlight
for photosynthesis more effectively
why is there variation in branching patterns
a finite amount of energy to devote to shoot growth
most of that energy goes into branching, there is less
available for growing tall
risk of being shaded by taller plants increases
what do shoot architectures optimize
ability to absorb light
what do variations in leaf size and structure cause
much of the outward diversity in plant form
where are species with largest leaves found
tropical rain forests
where are species with smallest leaves found
dry or very cold environments
arrangement of leaves on stems is called
phyllotaxy
describe phyllotaxy
genetically determined and programmed by the shoot apical meristem and is specific to each species
describe different 3 types of phyllotaxy
one leaf per node (alternate, or spiral, phyllotaxy)
two leaves per node (opposite phyllotaxy)
more leaves per node (whorled phyllotaxy)
describe phyllotaxy of angiosperms
alternate phyllotaxy
leaves arranged in an ascending spiral around the stem
successive leaf emerging 137.5° (angle minimizes shading of lower leaves)
plant features that…
reduce self-shading increase light capture
measurement for light capture
leaf area index
ratio of the total upper leaf surface of a single plant or an entire crop divided by the surface area
of the land on which the plant or crop grows
values up to 7 are common for mature crops
consequence of adding more leaves increasing shading of lower leaves to the point that they respire more than photosynthesize
nonproductive leaves or branches undergo programmed cell death and are eventually shed, a process called self- pruning
leaf orientation affects what
light capture
name the 2 leaf orientations
horizontal
vertical
leaf orientations in low light conditions
horizontal leaves capture sunlight much more effectively than vertical leaves
leaf orientations in high light conditions
horizontal orientation exposes upper leaves to overly intense light, injuring leaves and reducing photosynthesis
Vertical light rays are essentially parallel to the leaf surfaces, so no leaf receives too much light, and light penetrates more deeply to the lower leaves
how do the roots of many plants respond to low nitrate pockets
extending straight through the pockets instead of branching within them
how do the roots of many plants respond to rich nitrate pockets
often branch extensively there
synthesizing more proteins involved in nitrate transport and assimilation
Efficient absorption of limited nutrients is enhanced by
reduced competition within the root system of a plant
what are the evolution of mutualistic associations between roots and fungi called
mycorrhizae
describe mycorrhizae
Mycorrhizal hyphae provide the fungus and plant roots with an enormous surface area for absorbing water and minerals (phosphate)
name the 2 major pathways of transport
apoplast
symplast
describe apoplast
consists of everything external to the plasma membranes of living cells and includes cell walls, extracellular spaces, and the interior of dead cells such as vessel elements and tracheids
describes symplast
consists of the entire mass of cytosol of all the living cells in a plant, as well as the plasmodesmata, the cytoplasmic channels that interconnect them
name the 3 routes for transport within a plant tissue or organ
apoplastic
symplastic
transmembrane routes
describe apoplastic route
water and solutes move along the continuum of cell walls and extracellular spaces (like the way water moves through a sponge)
describe symplastic route
water and solutes move along the continuum of cytosol
route requires substances to cross a plasma membrane when they first enter the plant substances can move from cell to cell via plasmodesmata.
describe transmembrane route
water and solutes move out of one cell across the cell wall and into the neighbouring cells
requires repeated crossings of plasma membranes as substances exit one cell and enter the next
selective permeability of the plasma membrane controls
short-distance movement of substances into and out of cells
what types of transport do plants have
active and passive
what are plant cell membranes equipped with
same general types of pumps and proteins
channel proteins, carrier proteins, and cotransporters
difference between basic transport in animal and plant cells
unlike animal cells, hydrogen ions (H+) rather than sodium ions (Na+) play the primary role in basic transport in plant cells
what is membrane potential in plants
the voltage across the membrane is established mainly through the pumping of H+ by proton pumps
describe cotransport with H+
plant cells use the energy in the H+ gradient and membrane potential to drive the active transport of many different solutes
cotransport with H+ is responsible for absorption of neutral solutes
an H+/sucrose cotransporter couples movement of sucrose against its concentration gradient with movement of H+ down its electrochemical gradient
facilitates movement of ions (uptake of nitrate (NO3−) by root cells)
describe ion channels
only certain ions to pass
most channels are gated (opening or closing
in response to stimuli)
Ion channels are involved in producing electrical signals
absorption or loss of water. by a cell occurs by
osmosis
regions of high water potential to lower water potential
dependant on solute concentration
what is water potential
physical property that predicts the direction in which water will flow
water’s capacity to perform work when it moves from a region of higher water potential to a region of lower water potential
water potential formula
measured in pressure = megapascal
abbreviated psi
psi = psi p (pressure potential, directly proportional to molarity) + psi s (solute potential, osmotic potential)
psi of pure water in an open container
0 MPa
what is one Mpa =
10 times 101.3 kPa
internal pressure of a living plant cell due to the osmotic uptake of water is approximately
O.5 MPa
effect on water potential by an increase in solutes
negative effect
solute potential = always negative
describe pressure
solution is being withdrawn by a syringe = negative pressure; being expelled from a syringe = positive pressure water in living cells = positive pressure due to the osmotic uptake of water. the protoplast (the living part of the cell) presses against the cell wall = turgor pressure.
what does turgor pressure do
critical for plant function
helps maintain the stiffness of plant tissues
the driving force for cell elongation
water in hollow nonliving xylem cells (tracheids and vessel element)
negative pressure
what is wilting
effects of turgor loss
result of cell losing water
what does difference in water potential determine
direction of water movement across membranes
how dow water molecules move
diffuse across the phospholipid bilayer
what is aquaporins
the transport proteins that facilitate the transport of water molecules across membranes
channels are highly dynamic
what is the name of long distance transport
bulk flow
the movement of liquid in response to a pressure gradient
higher to lower pressure
where does bulk flow occur
tracheids and vessel elements of the xylem and within the sieve-tube elements of the phloem
what is efficient bulk flow due to
absence or reduction of cytoplasm
perforation plates at the ends of vessel elements
porous sieve plates connecting sieve-tube elements
where does absorption of water and minerals occur
root hair epidermal cells near the tips of roots
describe absorption of water and minerals by root epidermal cells
The root hairs absorb the soil solution (water molecules and dissolved mineral ions)
soil solution is drawn into the hydrophilic walls of epidermal cells and moves along the cell walls and the extracellular spaces into the root cortex enhances the exposure of the cells of the cortex to the soil solution = much greater membrane surface area for absorption
active transport enables roots to accumulate essential minerals
what must the water and minerals pass from before being transported to rest of plant
xylem of vascular cylinder or stele
what does the endodermis do in terms of transport
last checkpoint for the selective passage of minerals from the cortex into the vascular cylinder
describe transport through endodermis and symplast
minerals already in the symplast when they reach the endodermis continue through the plasmodesmata of endodermal cells and pass into the vascular cylinder
describe transport through endodermis and apoplast
encounter a dead end, blocks their passage into the vascular cylinder.
barrier is the Casparian strip water and minerals cannot cross the endodermis and enter the vascular cylinder via the apoplast
what must minerals and water passively moving through apoplast do
cross the selectively permeable plasma membrane of an endodermal cell before they can enter the vascular cylinder
the endodermis transports needed minerals from the soil into the xylem and keeps many unneeded or toxic substances out
prevents solutes that have accumulated in the xylem from leaking back into the soil solution
what is the last segment in the soil-to-xylem pathway
passage of water and minerals into the tracheids and vessel elements of the xylem
what is xylem sap
the water and dissolved minerals in the xylem
where does xylem sap get transport
to the veins that branch throughout each leaf
what does transporting xylem sap involve
loss of an astonishing amount of water by transpiration
when do plants wilt
when transpired water is NOT replaced by water transported up from the roots
what happens at night when there is almost no transpiration
root cells continue actively pumping mineral ions into the xylem
Casparian strip prevents the ions from leaking back out into the cortex and soil
resulting accumulation of minerals lowers the water potential within the vascular cylinder
water flows in from the root cortex, generating root pressure, a push of xylem sap.
what is guttation
more water to enter the leaves than is transpired
the exudation of water droplets that can be seen in the morning on the tips or edges of some plant leaves
what is dew
condensed atmospheric moisture
xylem sap is…
not pushed from below by root pressure but is pulled up
describe cohesion tension hypothesis
transpiration provides the pull for the ascent of xylem sap
the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots
xylem sap is under negative pressure or tension
what is transpirational pull
Stomata on a leaf’s surface lead to a maze of internal air spaces that expose the mesophyll cells to he CO2 they need for photosynthesis
air in these spaces is saturated with water vapour the air outside the leaf is drier so water vapour in the air spaces of a leaf diffuses down its water potential gradient and exits the leaf via the stomata
loss of water vapour by diffusion and evaporation that we call transpiration
what develops at the surface of mesophyll cell walls in the leaf
negative pressure potential that causes water to move up through the xylem
what does cell wall act as
very thin capillary network
what does water adhere to
the cellulose microfibrils and other hydrophilic components of the cell wall
what happens because of the high surface tension of water
curvature of the interface induces a tension, or negative pressure potential, in the water
more water evaporates = curvature of the air-water interface increases and the pressure of the water becomes more negative
water molecules from the more hydrated parts of the leaf are then pulled toward this area, reducing the tension
pulling forces are transferred to the xylem because each water molecule is cohesively bound by hydrogen bonds
the negative water potential of leaves provides the..
“pull” in transpirational pull
Consequence of climate change
increasing amount
of water vapour in the atmosphere = decreases the air’s water potential
With a smaller difference between the water potentials of the air spaces and the atmosphere
transpirational pull, and therefore xylem sap transport, will diminish = insufficient water delivered to meet the photosynthetic demands of the leaves
what does decreased xylem transport produce
deficiencies in essential nutrients required for the synthesis of biological molecules and growth
what is adhesion
attractive force between water molecules and other polar substances
strong attraction between water molecules and the cellulose molecules in the xylem cell walls
what is cohesion
attractive force between molecules of the same substance
water has an unusually high cohesive force bc hydrogen bonds
waters cohesive force within xylem has…
tensile strength equivalent to that of a steel wire of similar diameter
cohesion of water makes it possible to
pull a column of xylem sap from above without the water molecules separating
describe pulling of xylem sap
Water molecules exiting the xylem in the leaf tug on adjacent water molecules, and this pull is relayed, down the entire column of water in the xylem
the strong adhesion of water molecules to the hydrophilic walls of xylem cells helps offset the downward force of gravity
what is cavitation
the formation of a water vapour pocket
common in wide vessel elements
can occur during drought stress or when xylem sap freezes in winter
air bubbles resulting from cavitation expand and block water channels of the xylem (hydraulic failure)
Interruption of xylem sap by cavitation
not always permanent
chain of water molecules can detour around the air bubbles through pits between adjacent tracheids or vessel elements
what adds a layer of new xylem each year
secondary growth
what is the function of older secondary xylem
no longer transport water
provides support
how is bulk flow different from diffusion
driven by differences in pressure potential not solute potential
flow does not occur across plasma membranes of living cells instead = hollow dead cells
way faster
moves whole solution together
plant expends no energy to lift xylem sap by bulk flow
absorption of sunlight drives most of transpiration
what is translocation
transport of the products of photosynthesis
carried out by the phloem
what are sieve-tube elements
In angiosperms, the specialized cells that are conduits for translocation
what are inbetween sieve tube element cells
sieve plates, structures that allow the flow of sap along the sieve tube
what is phloem sap
aqueous solution that flows through sieve tubes
made of sugar
contains amino acids, hormones and minerals
how does phloem sap move
phloem sap moves from sites of sugar production to sites of sugar use or storage
What is a sugar source
plant oran that is a net producer of sugar by photosynthesis or by breakdown of starch
what is a sugar sink
organ that is a net consumer or depository of sugar
growing roots, buds, stems, fruits
what is a storage organ
tuber or a bulb
may be a source or a sink, depending on the season stockpiling carbohydrates in the summer = sugar sink
breaking dormancy in the spring = sugar source (starch is broken down to sugar, which is carried to the growing shoot tips)
where do sinks receive sugar from
Nearest sugar sources
direction of transport for each sieve tube depends on
locations of the sugar source and sugar sink that are connected by that tube
describe route through the sieve tube elements
sugar is loaded into them
sugar is unloaded at sink end of tube
process varies by species and organ
concentration of free sugar in sink is always lower than in the sieve tube because unloaded sugar is consumed during growth and metabolism of the cells of the sink or converted to insoluble polymers like starch
result of sugar gradient concentration =
sugar molecules move by facilitated diffusion from phloem to sink tissues and water follows by osmosis
Consequences of loss of phloem function
sugar transport becomes severely compromised and the end result is typically death of the tree within 5 years of infection
how does phloem sap move through sieve tubes of angiosperms
by bulk flow driven by positive pressure = pressure flow
describe pressure flow process
1=sugars are loaded into the phloem sap by source cells
2=movement of solutes lowers water potential of phloem sap in region, causes water to enter nearby cells and xylem, resulting increase in water pressure forces phloem sap to move along tubes
3=at sink cells, sugars are unloaded
4=increases water potential and causes water to leave phloem sap and enter neighbouring cells and xylem vessels, xylem recycles the way from sink to source
what do sinks vary in
energy demands and capacity to unload sugars
what is self thinning
more sinks than can be supported by sources
plant might abort some flowers, seeds, or fruits
true or false
transport needs of a plant cell typically change during its development
true
what does water stress activate
signal transduction pathways that greatly alter the membrane transport proteins governing the overall transport of water and minerals
what is symplast responsible for
dynamic changes in plant transport processes
what are plasmodesmata
highly dynamic components of the symplast
can change in permeability and number
open or close rapidly in response to changes in turgor pressure, cytosolic Ca2+ levels, or cytosolic pH
form during cytokinesis or much later
what can plasmodesmata do when a leaf matures from sink to source
either close or are eliminated, causing phloem unloading to cease
what do plant viruses produce
viral movement proteins that cause plasmodesmata to dilate, enabling viral RNA to pass between cells
plant cells themselves regulate plasmodesmata as part of a communication network
Viruses subvert this network by mimicking the cell’s regulators of plasmodesmata
what are symplastic domains
high degree of cytosolic interconnectedness exists only within certain groups of cells and tissues
informational molecules, such as proteins and RNAs, coordinate development between cells within each symplastic domain
phloems transport is
systemic
transports macromolecules lile proteins and various types of RNA
electrical signalling in phloem
dynamic feature
stimulus in one part of a plant can trigger an electrical signal in the phloem that affects another part, where it may elicit a change gene transcription, respiration, photosynthesis, phloem unloading, or hormonal levels
the phloem can serve a nerve-like function
what increases rate of photosynthesis and also increases water loss by stomata
large surface areas and high surface-to-volume ratios
what limits water loss
waxy cuticle
guard cells control the diameter of the stoma by changing shape
amount of water lost by leaf depends on
number of stomata and the average size of their pores.
stomatal density of a leaf is controlled by
genetic and environmental control
what leads to increased density
high light exposures and low CO2 levels during leaf development
in angiosperms cell wall of guard cells is
uneven in thickness, and the cellulose microfibrils are oriented in a direction that causes the guard cells to bow outward when turgid
when cells loose water the guard cells
become less bowed and pore closes
changes in turgor pressure in guard cells come from
reversible absorption and loss of K+
Stomatal closing results from
loss of K+ from guard cells to neighbouring cells, which leads to an osmotic loss of water
what do aquaporins do
help regulate the osmotic swelling and shrinking of guard cells
stomata during day and night
stomata are open during the day and mostly closed at night
stomatal opening at dawn
light, CO2 depletion, and an internal “clock” in guard cellds
explain how stomata open with light
stimulates guard cells to accumulate K+ and become turgid triggered by blue light receptors stimulates proton pumps
explain how stomata open with CO2 depletion
CO2 concentrations decrease during the day, the stomata progressively open if sufficient water is supplied to the leaf
explain how stomata open internal clock
Cycles with intervals of approximately 24 hours are called circadian rhythms
what causes stomata to close during day
Environmental stresses, such as drought, high tempera- ture, and wind
plant has a water deficiency
guard cells may lose turgor and close stomata
hormone called abscisic acid (ABA) leaves
reduces wilting but also restricts CO2 absorption
how do plants respond to mild drought stress
rapidly closing stomata
how do plants respond to prolonged drought stress
leaves can become severely wilted and irreversibly injured
Transpiration also results in…
evaporative cooling
lower a leaf’s temperature by 10°C compared with the surrounding air
cooling prevents the leaf from reaching temperatures that could denature enzymes involved in photosynthesis and other metabolic processes
what is a major determinant of plant productivity
water availability
plants adapted to arid
xerophytes
adaptations of xerophytes
unusual physiological or morphological adaptations
stems of many xerophytes are fleshy, they store water for use during long dry periods
crassulacean acid metabolism (CAM), a specialized form of photosynthesis - takes place in CO2 at night = he stomata can remain closed during the day
