Bio9 Flashcards
91 What is the vein
composed of, and
describe their
functions.
xylem and phloem.
Xylem is in charge of water transport in the plant,
while phloem is in charge of transport of sugar
(glucose) inside the plant.
9.1 Describe and
explain the process
of transport of
water (capillary
action) in plants.
The cohesive property of water and adhesive
property of water and evaporation generate
tension forces in leaf cell walls. The low pressure
generated from the force of adhesion between
water and cell walls in the leaf is strong enough
to suck water out of the xvlem.
**water flows from high pressure to low pressure
The low pressure generates a pulling force
transmitted through the water in the xylem vessels
down and to the ends of the xylem roots to
create a transpiration-pull to move water
upwards against the force of gravity.
9.1 What factors
allow the xylem
vessels to transport
under tension.
The cohesive property of water, as water
molecules are polar and partial negative charge
on the oxygen atom attracts the hydrogen atom
in a neighboring water molecule.
Thickened walls of xylem vessels and the
structure of lignin constructre is present to allow
the xylem to withstand very low pressures without
collapsing.
91 How do roots
absorb water and
mineral ions present
from the soil?
Explain the
processes
- Osmosis: Active uptake of mineral ions results in
a higher concentration of minerals in plants than
in the surrounding soil. Water moves from low
solute to high solute concentration. - A mutualistic relationship with fungal hyphae:
fungus are grown on surface of even cells of the
roots. They grow out into the soil and absorb
mineral ions and supply it to the roots. - Active transport (cations and anions): minerals
are larger than water molecules.
a. minerals bound to soil particles
b. Example of 3 nutrients (minerals): phosphate,
nitrate, magnesium. Iron, calcium, potassium,
sodium, etc.
C. Minerals dissolve in water
d. Mass flow causes movement of minerals and
with movement of water through soil
e. Minerals diffuse down a concentration gradient
towards roots (as the mineral concentration next
to the roots is continuously decreasing)
f. Minerals enter the plant through roots
g. By active transport, ATP
h. Root hairs increase SA
i. Hypha of (mutualistic fungi) may enhance water
movement of selected ions into roots/increase SA
j. Root hairs have many mitochondria
k. Export of H+ ions create electrochemical
gradient/displaces ions bound to soil
L. That causes positive mineral ions to diffuse into
root cells
m. Negative mineral ions cross member linked to
H+ions moving down (H+) gradient
9.1 Skill: Drawing the
structure of primary
xylem vessels in
sections of stems
based on
microscope images.
When drawing the structure of primary xylem
vessels, it is important to remember the following
features:
- Vessel elements should be drawn as a
continuous tube (tracheids will consist of
interlinking tapered cells)
-The remnants of the fused end wall can be
represented as indents (these forms perforated
end plates)
-The xylem wall should contain gaps (pits), which
enable the exchange of water molecules
Lignin can be represented by either a spiral
(coiled) or annular (rings) arrangement
9.1 Application:
Describe simple
models of water
transport, inclusive
of evaporation,
adhesion and
cohesion.
Capillary Tubing:
-water can flow along narrow spaces in
opposition to external forces like gravity
(capillary action)
-due to a combination of surface tension
(cohesive forces) and adhesion with the walls of
the tube surface
-thinner the tube or the less dense the fluid, the
higher the liquid will rise
Filter Paper:
-filter paper (or blotting paper) will absorb water
due to both adhesive and cohesive properties
-when placed perpendicular to a water source,
the water will hence rise up along the length of
the paper
-comparable to the movement of water up a
xylem (the paper and the xylem wall are both
composed of cellulose)
Porous Pots:
-semi-permeable containers that allow for the
free passage of certain small materials through
pores
-loss of water from the pot is similar to the
evaporative water loss that occurs in the leaves of
plants
-porous pot is attached by an airtight seal to a
tube, the water loss creates a negative pressure
that draws more liquid
9.1 Skill: Design of
an experiment to
test hypotheses
about the effect of
temperature or
humidity on
transpiration rates.
-Experiments can be designed using potometers
Temperature:
-use heat lamp to vary the temperature
-use infrared thermometer to measure leaf
temperature
in very high temperatures the stomata may close
Humidity:
-use a transparent plastic bag to enclose the
leafy shoot
-use mist sprayer to raise humidity inside the
bag
-use dessicant bag and silica gel to lower
humidity
-use electronic hygrometer to measure the
relative humidity
Wind speed:
-use electric fan to generate air movement
-velocity can be varied by changing the distance
of the fan or the rate of rotation
-Use anemometer to measure the speed of fan
moving across the plant leaves
High velocities can cause stomata to close
9.1 What causes the
hydrogen to bond,
and what makes it
strong?
His 1+ and O is 2-. Individually the bond of H2O is
weak, but when a water molecule and bind to four
other water molecules, all the bonding makes it
strong.
9.1 What is
produced to force
closure of the
stomata?
The hormone abscisic acid
9.1 Why don’t xylem
cells contain any
cytoplasm?
It is a dead cell. It grows into size, and remains
dead to provide larger lumen making water
transport more efficient.
9.2 Application:
Structure-function
relationships of
phloem sieve tubes.
What are phloem
sieve tubes
primarily composed
of and what are
their individual
functions?
Phloems are living cells unlike xylem, and they
together make up the vascular bundle.
-have reduced quantities of cytoplasm and no
nucleus to maximize transport
-living because membrane helps to maintain the
sucrose and organic molecule concentration that
has been established by active transport.
-rigid cell walls of sieve tube cell: allow for the
establishment of the pressure necessary to
achieve the flow of phloem in the sieve tube cell.
-sieve plates: perforated walls that separates
individual sieve tube cells; helps connect sieve
tubes at transverse ends
-the perforated walls in combination with the
reduced cytoplasm means that the resistance to
the flow of phloem sap will be lower.
-companion cells: contains organelles to help
support the function of sieve tubes, as it has
minimal organelles and less cytoplasm; it contains
a lot of mitochondria to support the energy used
of sieve tube cells
-lumen: the space in the sieve tube cells to enable
transport of sugars
-plasmodesmata: connects cytoplasm of sieve
tube membrane and companion cells
9.2 Describe the
process of
translocation in
phloem.
Plants differ in the mechanism for phloem loading.
Original
六
Apoplastic route:
-sucrose: mesophyll cells -> through cell walls ->
cell walls of companion cells -> sieve cells ->
sucrose transport protein then actively transports
the sugar in.
-a concentration gradient of sucrose is
established by active transport
-hydrogen ions are actively transported out of the
companion cell from surrounding tissues using
ATP as an energy source
-build-up of hydrogen ions then flows down its
concentration gradient through a co-transport
protein.
-the energy released is used to carry sucrose into
the companion cell-sieve tube complex.
Symplastic route:
-companion cells load sucrose into phloem by
allowing
materials to pass into the sieve tube via
interconnecting plasmodesmata
Transport of surcrose:
-high concentrations of solutes in the phloem at
the source lead to water uptake by osmosis.
-hydrostatic high pressure due to increase of water moves phloem sap downward.
-incompressibility of water allows transport along
hydrostatic pressure (pressure in liquid) gradients
-phloem sap moves downward into sink cell.
-companion cells unload organic molecules into
sink, and sucrose is stored
9.2 Skill: Analysis of
data from
experiments
measuring phloem
transport rates
using aphid stylets
and radioactively-
labelled carbon
dioxide. Describe
how translocation
rate is measured in
this experiment.
-aphids consume phloem sap as the main
component of their diet.
-CO2 in the bag is radioactive labelled, which
functions as an indicator to see how far the
phloem sap has travelled.
-experimenters feed Aphids at certain distances
(20cm, 40cm, etc), and severe their stylets.
-if the aphid is anaesthetised and the stylet
severed, phloem will continue to flow out of the
stylet and both the rate of flow and the
composition of the sap can be analysed.
-the phloem sap that comes out are then
analyzed for the presence of radioactive labelled
sugars.
-the closer the stylet is to the sink, the slower the
rate at which the phloem sap will come out.
The rate of translocation can then be calculated
based on the time taken for the radioisotope to
be detected at different positions. (distance (cm)/
time (hr)) which the rate is cm/hour.
-release radiation from CO2 that can be detected
either using film or radiation detectors.
9.3 What are the
undifferentiated
cells in plants and in
what ways does it
allow growth?
Undifferentiated cells in the meristems of plants
allow indeterminate growth (it keeps growing).
There are apical (primary growth) and lateral
meristems (secondary growth).
Apical Meristems:
Found at the terminal bud of the stem and the
root tip. It has indiscriminate growth (add length
and size).
Auxiliary buds are inactive meristems: when the
plant flowers or produces a new shoot, the
hormonal inhibitor is removed and the meristem
becomes active.
Lateral Meristems:
Its growth results in extra (secondary) xylem
growth in a ring inside the cambium. Cork
cambium produces cord, which we know as bark.
Secondary phloem also grows.
9.3 Describe the
process of mitosis in
meristematic cells
and its function.
Mitosis and cell division in the shoot apex provide
cells needed for extension of the stem and
development of leaves.
When a meristematic cell divides, it replicates
more small meristematic cells AND differentiates
into a specialized cell of the plant body required
for growth.
The products of this meristematic cell division
produce cells for plant growth while maintaining
the meristematic tissue necessary for future and
ongoing growth.
9.3 What is the
name of the plant
hormone, and what
are its functions in
plants?
Auxin controls growth and cell division within the
shoot apex
Auxin is produced and plant shoots grow and
respond to the environment by tropisms
9.3 How do plants
grow depending on
the environmental
conditions?
Describe the
process
-auxin is produced by cells in the apical meristem.
-direction of light is detected at the tip of the
shoot by pigments called phototropins.
-phototropins stimulated by the absorption of
light regulate the transport of auxin.
-auxin efflux pumps can set up concentration
gradients of auxin in plant tissue, and elongates a
side of the plant for it to bend towards sunlight.
The location of auxin efflux pumps determines the direction of transport.
-when a shoot is exposed to light from above,
auxin efflux pumps are located at the base of the
cells in the shoot apex.
-auxin is transported downwards from the
meristem, and has an equal distribution in the cells
below the meristem.
-cells elongate and the shoot grows straight
upwards, symmetric growth.
-auxin is moved to the opposite side (shady side)
of the growing shoot by PIN3 proteins.
-auxin (IAA) activates H proton (H+) pump of
shoot cells furthest from light source.
-H+ pump moves H+ ions from the cytoplasm to
the cell wall, which causes a decrease in pH level.
-A decrease in pH breaks hydrogen bonds in the
cellulose of the cell walls of cells away from the
light.
-cellulose fibers loosen and allows cell to expand as turgor pressure inside the
cell pushes against the cell wall; as a result, that part of the stem elongates
which turns to light.
-auxin causes a rapid increase in the expression of genes coding for the proton
pump and cell wall loosening proteins.
9.3 How can auxin
influence cell
growth rates?
Auxin influences cell growth rates by changing
the pattern of gene expression, and influencing
the pH level.
In plant shoots, auxin promotes cell elongation.
In plant roots, auxin inhibits cell elongation.
1. An auxin-receptor complex is formed when
auxin binds with receptors in the transcriptional
repressor cells.
2. Auxin-receptor complex binds with repressor
of DNA (that codes for growth-stimulating genes)
3. The binding with the repressor breaks down of
the repressor, which growth stimulating genes are
transcribed, and causes growth.
4. Growth in which the expression of these genes
causes secretion of hydrogen ions into cell walls,
allowing cell expansion.
9.4 Describe how
flowers are grown
out of plants in
order for plants to
reproduce.
Flowering involves a change in gene expression in
the shoot apex. Light plays a role in the
production of either inhibitors or activators of
genes that control flowering.
1. When proper phototropic conditions are
perceived by the leaf, the companion cells
induces florigen that moves through the phloem
into the shoot apex.
2. Florigen causes changes in gene expression in
shoot apex, which activates transcription of floral
meristem genes, resulting in flower initiation.
3. Shoot apical meristem produces flowers
instead of leaves.
9.4 Describe how
plants response to
the length of light
and dark periods.
The switch to flowering is a response to the
length of light and dark periods in many plants.
1. Plants respond to periods of darkness using a
leaf pigment called phytochrome. This pigment
can exist in two inter-convertible forms - inactive
Pr and active Pfr.
2. Pr converts to Pfr when there is red light of
(660nm).
3. Pfr converts to Pr when there is a far red lig ht
of (730nm)
4. With that being said, darkness (far red light of
730nm) causes the very slow conversion of Pfr to
Pr.
5. In SDP, Pfr acts as an inhibitor to the genes
which bring about flowering. So when there is
long nights, the inhibitor is removed
(interconverted into Pr), which promotes growth.
6. In LDP, Pfr the remaining Pfr at the end of a
short night stimulates the plant to flower by acting
as a promoter to genes which bring about
flowering.
9.4 Application:
What methods are
used to induce
short-day plants to
flower out of
season? Provide an
example.
Chrysanthemums, for example, is a SDP.
1. To keep the plant in a vegetative state, growers
can stimulate the plant with a flash of light to stop
the process of interconversion into Pr.
2. Growers can keep the hours of darkness less
than critical night length.
3. Growers can cover an opaque clack cloth on
plant for around 12 hrs a day to ensure critical
night length.
*Flowering is stimulated by long nights rather than
short days.
9.4 What
relationship does
plant have with the
pollinators, and
what are the
benefits?
Most flowering plants use mutualistic relationships
with pollinators in sexual reproduction. Pollen can
be transferred by wind or water, but is commonly
transferred by animals (called pollinators).
Some examples of pollinators include birds, bats
and insects (including bees and butterflies)
Bees gain food in the form of nectar when they
carry out pollination of many flowering plants.
Both honey bee and plant are helped by this
association.
9.4 What are the
stages to plant
reproduction?
Success in plant reproduction depends on
pollination, fertilization and seed dispersal.
Pollination:
-transfer of pollen grains from an anther (male
plant structure) to a stigma (female plant
structure)
-many plants possess both male and female
structures (monoecious) and can potentially self-
pollinate
-from an evolutionary perspective, cross-
pollination is preferable as it improves genetic
diversity
Fertilisation:
-fusion of a male gamete nuclei with a female
gamete nuclei to form a zygote
-in plants, the male gamete is stored in the pollen
grain and the female gamete is found in the ovule
Seed dispersal:
-fertilisation of gametes results in the formation of
a seed, which moves away from the parental plant
-this seed dispersal reduces competition for
resources between the germinating seed and the
parental plant
-there are a variety of seed dispersal mechanisms,
including wind, water, fruits and animals
-seed structure will vary depending on the mechanism of dispersal employed by the plant
9.4 Skill: Drawing of
half-views of
animal-pollinated
flowers. List out the
structures in animal
pollinated flowers
and briefly
mentions its
functions.
Stamen (male part):
-anther: pollen producing organ
-filament: supports anther (makes it accessible to
pollinators)
Carpel (female part)
-stigma: sticky, receptive tip of the pistil that is
responsible for catching the pollen; contains
nectar
-style: tube-shaped connection between the
stigma and ovule; elevates stigma
-ovary (with ovule inside): structure that contains
the female reproductive cells; will develop into
seed after fertilization.
-petal: attract pollinators
-sepal: outer covering which protects the flower
when in bud.
-receptacle: stalk of the flower
9.4 Skill: Drawing
internal structure of
seeds. List out the
structures of the
seed and its
functions.
-testa (outer layer)
-cotydelon: contain the nutrients of the bean
seed.
-plumule (embryonic shoot)
-radicle (embryonic root):
-micropyle: allows for the passage of water;
where the seed was attached to the parent plant
9.4 Skill: Design of
experiments to test
hypotheses about
factors affecting
germination.
Aim: The aim is to find the relationship between
the pH level (5,6,7,8,9) and the length of Vigna
radiata roots after 5 days of growth.
Method: The level of pH will be controlled by
using vinegar for acid concentrations and baking
soda for base concentrations, and solution will be
tested by pH strip.
Control Variables:
-under room temperature (same temperature)
-under same environment (same 02 level)
-will be placed in a cupboard (no light)
-will be given the same amount of solution (50 mL
each time)
-will be qiven water on the same time each day
9.1 Draw a labelled
diagram showing
the tissues present
in a dicot leaf.
upper and lower epidermis;
• palisade mesophyll under upper epidermis
• 3 to 1
• 2 of leaf thickness;
• spongy mesophyll/layer in lower half of leaf;
• vein showing separate areas of xylem above
phloem;
• stoma/stomata labelled in (lower) epidermis;
• two guard cells; (at least one must be labelled
for mark)
9.1 Explain the
functions of the
different tissues of
the leaf.
cuticle (produced by epidermis) prevents water
lOSS
• epidermis protects cells inside the leaf
• stomata (in epidermis) for gas exchange
• palisade parenchyma / mesophyll / layer for
photosynthesis
• spongy parenchyma / mesophyll / layer for
photosynthesis
• air spaces for diffusion of 02 / CO2 / gases
• spongy mesophyll for gas exchange /
absorption of CO2
• xylem transports water / mineral salts / ions to
the leaves
• phloem transports products of photosynthesis /
sugars (to flowers / new leaves / stem / roots /
fruit)
• stomata allow transpiration (which helps transport of mineral nutrients)
• quard cells open and close stomata
• guard cells close stomata to reduce
transpiration
9.1 Outline the
adaptations of plant
roots for absorption
of mineral ions from
the soil.
mineral ions are absorbed by active transport;
• large surface area;
• branching (increases surface area);
• root hairs:
• root hair cells have carrier protein/ion pumps (in
their plasma membrane);
• (many) mitochondria in root (hair) cells;
• to provide ATP for active transport;
• connections with fungi in the soil/fungal hyphae;
9.1 Describe the
process of mineral
ion uptake into
roots.
• absorbed by root hairs / through epidermis
• root hairs increase the surface area for
absorption
• uses active transport / uses ATP / uses energy
• Use of proteins / pumps to move ions across
membrane
• against concentration gradient / diffusion
gradients into cell / root
• can enter cell wall space / be drawn through
cell walls / apoplastic pathway
• selective / only specific ions absorbed
9.4 Explain the
conditions needed
for seed
germination.
• water needed
• water causes swelling which bursts the testa /
seed coat / water softens the testa / seed coat
• water mobilises soluble food reserves /
enzymes / medium for metabolic processes
• water rehydrates cells / tissues
• water transports hydrolysed food reserves
• water transports growth promoters / hormones
• water dilutes / washes out growth inhibitors
• oxygen needed
• oxygen required for (aerobic) respiration
• which provides ATP for metabolic activity
• warmth increases enzyme activity (reject
enzymes denatured)
• fire breaks down inhibitors
• chilling breaks down inhibitors
• light breaks down inhibitors / stimulates
germination in some species
• degradation of testa makes it more permeable
to water / gases
9.1 Define
transpiration.
Transpiration is the loss of water vapour from the
stems and leaves of plants.
9.1 Explain gas
exchange that
occurs through leaf
stomata.
-the leaf is adapted for gas exchange and to
absorb sunlight
- for photosynthesis, mesophvil cells in the leaf
require carbon dioxide and water
-oxygen must be lost
-carbon dioxide must enter
-they pass into and out of the leaf via stomata
(typically in the lower eperdermis) by diffusion /
down the concentration gradient;
-gases/02/CO2 move through air spaces in the
spongy (mesophyll);
-CO2 dissolves in moisture in (mesophyll) cell
walls;
-photosynthesis maintains concentration
gradients/high O2 and low CO2 in the leaf;
Stomata are pores on the underside of the leaf
which facilitate gas exchange (needed for
photosynthesis)
-quard cells open stomata for gas exchange
-allow water vapour within the air spaces in the
spongy mesophyll to diffuse out of the leaf
-the air spaces in the mesophyll contain very
humid air due to the evaporation of water from
the mesophyll cells
• Transpiration is the inevitable consequence of gas exchange in the leaf
9.1 Explain
structures and
mechanisms
involved in the flow
of water from roots
to leaves.
• Plants transport water from the roots to the
leaves to replace losses from transpiration
Water entering roots:
-active transport of solutes from soil into roots:
-draws water by osmosis
-carried through xylem vessels;
Water being sucked up:
-water is lost from the leaves of the plant when it
is converted into vapor (evaporation) and
diffuses from the stomata
-some of the light energy absorbed by leaves is
converted into heat, which evaporates water
within the spongy mesophyll
-vapour diffuses out of the leaf via stomata, and
-new water is absorbed from the soil by the roots;
creating a negative pressure gradient within the
leaf
• The adhesive property of water and evaporation
generate tension forces in leaf cell walls
-water pulled up due to capillary action/
cohesion/adhesion;
-adhesion of water to the inside of the xvlem
helps move water up;
-cohesion of water to itself enhances water movement up the xylem
-water diffuses into air spaces (in spongy
mesophyll) of leaves;
-continuous column of molecules/transpiration
stream:
-negative pressure creates a tension force in leaf
cell walls which draws water from the xylem
(transpiration pull)
-the water is pulled from the xylem under tension
due to the adhesive attraction between water and
the leaf cell walls
-water will flow, via the xylem, along the pressure
gradient to replace the water lost from leaves
(transpiration stream)
-guard cells control the rate of transpiration pull/
evaporation;
Structure:
-root hairs provide a large surface area for water
uptake;
-xvlem is thin in structure; allows water to flow
along narrow spaces in opposition to external
forces like gravity (capillary action)
-cellulose wall with rings of lignin give strength to
resist (low) pressure;
9.1 Explain the
regulation of water
loss in plants.
*this question is out
of our syllabus
The amount of water lost from the leaves
(transpiration rate) is regulated by the opening
and closing of stomata
-guard cells flank the stomata and can occlude
the opening by becoming increasingly flaccid in
response to cellular signals
-when a plant begins to wilt from water stress,
dehydrated mesophyll cells release the plant
hormone abscisic acid (ABA)
-abscisic acid triggers the efflux of potassium
from guard cells, decreasing water pressure
within the cells (lose turgor)
-a loss of turgor makes the stomatal pore close,
as the quard cells become flaccid and block the
opening
-transpiration rates will be higher when stomatal
pores are open than when they are closed
-stomatal pores are responsible for gas exchange
in the leaf and hence levels of photosynthesis will
affect transpiration
-other factors that will affect transpiration rates
include humidity, temperature, light intensity and
wind
91 Describe
structure of xvlem.
-has a continuous tube (tracheids will consist of
interlinking tapered cells)
-remnants of the fused end wall can be
represented as indents (these forms perforated
end plates)
The xylem wall should contain gaps (pits), which
enable the exchange of water molecules
Lignin can be represented by either a spiral
(coiled) or annular (rings) arrangement
The structure of xylem vessels allows them to
transport water inside plants very efficiently.)
-long continuous tubes, allows them to transport
water over long distances with little obstruction
to the movement of water.
-walls are thickened with cellulose and lignin (a
waterproof polymer with high tensile strength)
-in the first xylem vessels formed (primary xylem),
the lignin is deposited in rings or spiral; allow the
cells to elongate in the growing tips of the plant.
-in regions that are no longer growing, more
lignin is deposited, forming very rigid vessels.
-lignin reinforces the vessels so they will not
collapse when transporting water under tension.
-pits (non-lignified regions) in the side walls of
xylem vessels allow water and mineral ions to
enter and exit the vessels.
9.1 Explain how
xylem is able to
maintain rigidity
even under low
pressure or
mechanical
disturbance.
The xylem is a specialised structure that functions
to facilitate the movement of water throughout
the plant
-thickened cellulose + reinforced by lignin
-walls are thickened, and the thickenings are
impregnated with a polymer called lignin;
strengthens the walls, so that they can withstand
very low pressures without collapsing.
-pressure inside xylem vessels is usually much
lower than atmospheric pressure but the rigid
structure prevents the xylem vessels from
collapsing.
-xylem vessels are formed from fles of cells,
arranged end-to-end, forms a continuous tube;
resulting in a faster rate of water transfer
It is a tube composed of dead cells that are
hollow (no protoplasm) to allow for the free
movement of water
2 types of lignin:
-annular vessels: the lignin forms a pattern of
circular rings at equal distances from each other
-spiral vessels: the lignin is present in the form of
a helix or coil
9.1 Outline polarity
of water molecule.
-water molecules are polar and can form a tvoe
of intermolecular association called a hydrogen
bond
-partial negative charge on the oxygen atom in
one water molecule attracts the hydrogen atom in
a neighboring water molecule.
9.1 Define cohesion.
Cohesion is the force of attraction between two
particles of the same substance (e.g. between two
water molecules)
9.1 Explain the
decrease in
pressure and
transpiration-pull
that results from
evaporation of
water from the leaf.
• transpiration is water loss (from plant) by
evaporation;
• flow of water through xylem from roots to
leaves is the transpiration stream;
-due to their dipolarity, water molecules are
attracted to hydrophilic surfaces of other
materials. -adhesion between water molecules
and the cellulose cell walls of leaf mesophyll
cells.
• evaporation from spongy mesophyll cells due to
heat generated from photosynthesis;
• replaced by osmosis from the xylem;
• (diffusion of water vapor) through stomata
because the low pressure is enough to suck water
out;
• water lost replaced from xylem / clear diagram showing movement of water from xylem through
cell(s) (walls) to air space;
• water pulled out of xylem creates suction/low
pressure/tension; transpiration pull results;
• water molecules stick together/are cohesive;
• due to hydrogen bonding/polarity of water
molecules;
• xylem vessels are thin (hollow) tubes;
-cellulose cell wall is made of many cellulose
fibers and has a porous structure which water can
move through by capillary action
• adhesion between water and xylem due to
polarity of water molecules;
• creates continuous column/transpiration stream:
The combination of evaporation and adhesion
between water and cellulose creates a tension
force which moves water via the xylem from the
roots to the leaves.
9.1 Outline why
roots are
hypertonic relative
to the soil.
-pumping of mineral ions into root hair cell
creates a higher solute concentration in the roots
than in the soil
-greater solute concentration = roots are
hypertonic relative to the soil
91 Outline the role
of active transport
in maintaining root
tonicity.
-root hair cells have a range of protein pumps
embedded in their plasma membranes
-protein pumps transport ions against their
concentration gradient into root hair cells.
-roots need a supply of oxygen to make ATP by
aerobic respiration for active transport.
9.1 Describe how
water enters roots
from the soil and
transported
throughout the
plant.
a. active transport of solutes from soil into roots;
b. draws water by osmosis
c. root hairs provide a large surface area for
water uptake:
d. carried through xylem vessels;
e. transpiration is the loss of water (vapour) from
leaves and stems / stomata;
f. (transpiration) creates suction/pull/negative
pressure;
g. cellulose wall with rings of lignin give strength
to resist (low) pressure;
h. water pulled up due to capillary action/
cohesion/adhesion;
i. continuous column of molecules/ transpiration
stream;
91 Compare the
symplastic and
apoplastic
pathways of water
transport through
the root.
Once inside the root, water will move towards the
xylem either via the cytoplasm (symplastic) or via
the cell wall (apoplastic)
Symplastic pathway:
-water moves continuously through the cytoplasm
of cells (connected via plasmodesmata)
Apoplastic pathway:
-water cannot cross the Casparian strip and is
transferred to the cytoplasm of the endodermis
-water and minerals flow in an upward direction
via the apoplast to the xylem in the root.
9.1 Define
xerophyte and
halophytic.
xerophyte: a plant that is adapted to grow in very
dry conditions, such as deserts
halophyte: a plant that is adapted to grow in
saline solutions
9.1 Application:
Outline strategies
used by xerophytes
and halophytes to
reduce water loss.
Xerophytes:
-blooms in a certain season
-less stomata
-deeper roots
-rolled leaves or spines, waxy cuticles, hair like
cells on leaves
-have spines (reduced leaves) so there is less
surface area for water loss
-example of xerophytes are CAM plants (crassulacean acid metabolism).
-alternative photosynthesis: CO2 is absorbed at
nigh and stored as C4 compound, and used in the
day when there is sunlight to perform
photosynthesis/ or stomata take in CO2 a lot
faster in the day
-have water storage cells in the stem so the stems
become swollen with water
-have a columnar structure (vertical branches)
which means less surface area is exposed during
the midday sun
Halophytes:
-becomes succulent (store water, dilute slat
concentrations)
-salt gland (secrete salt)
-vacuoles (compartmentalize NaCl, preventing
toxicity)
-sunken stomata & developed cuticle, shedding of leaves (stem takes over photosynthesis)
91 Describe the use
of a potometer to
measure
transpiration rates.
A potometer is a device that is used to estimate
transpiration rates by measuring the rate of water
loss / uptake
-plant is affixed to the potometer, transpiration
can be indirectly identified by the movement of
water
-water movement can be assessed as a change in
meniscus level or by the movement of an air
bubble towards the plant
-initial starting position of the meniscus or air
bubble can be adjusted by introducing additional
water from a reservoir
*not all water is lost to transpiration
-a small amount of water (~2%) is used in
photosynthesis and to maintain the viable turgidity
of plant cells
9.1 Explain the
factors that can
affect transpiration
in a typical
terrestrial plant.
(transpiration is) loss of water vapour from the
leaves/stomata (and stems) of plants;
temperature, humidity, light (intensity) and wind all
affect transpiration;
high temperatures increase evaporation rate of
water/transpiration;
d. more transpiration/water loss as temperature
rises/with more heat;
e. faster diffusion / more kinetic energy (of water
molecules);
f. faster evaporation (due to more latent heat
available);
(accept converse)high humidity lowers the rate of
water evaporation/transpiration;
b. air spaces inside leaf are saturated/nearly
saturated (with water vapour);
C. smaller concentration gradient with higher
atmospheric humidity;
(accept converse)air currents/wind increase water
evaporation/transpiration;
g. more transpiration/water loss as wind (speed)
increases;
h. humid air/ water vapour blown away from the
leaf;
I. increasing the concentration gradient (of water vapour);
j. more transpiration/water loss in the light;
(accept converse)high light (intensity)/sunlight
(usually) increases photosynthesis/water
evaporation through the stomata/transpiration;
stomata open to allow gaseous exchange/entry
of CO2;
abscisic acid stimulates closing of stomata;guard
cells open/close the stomata;
vapour);
j. more transpiration/ water loss in the light;
(accept converse)high light (intensity)/sunlight
9.1 State a similarity
and a difference
between
transpiration
models and
transpiration in
plant tissues.
Blotting/filter paper:
-no evaporation in model
-paper towel has no tube
-Xylem has lignin to keep its structure but the
paper towel does not
Porous pots:
-the pores in the model can’t open and close
-there are no pores in the xylem
D
Capillary tubing:
-no evaporation in the tube
-size differes
9.2 Define
translocation,
phloem sap, source
and sink.
Translocation: transport of organic solutes in a
plant
Phloem sap: the substance in which organic
compounds are transported from sources to sinks
Source: a site where organic compounds are
loaded into the phloem
Sink: a site where compounds are unloaded from
the phloem
9.2 List example
source and sink
tissues.
Sources:
-mature leaves
Sinks:
-roots
-tubers
-developing fruits
-immature leaves
9.2 Explain why
phloem transport
can be bidirectional.
Phloem transport is bidirectional because sucrose
gets accumulated in the phloem tissue and
absorbs water creating a high turgor pressure.
Hence the water flows from regions of high
turgor pressure to low turgor pressure and the
direction can be upwards or downwards from the
leaves based on the gradient.
9.2 Outline why
pressure in the
phloem increases
due to the
movement of water
into the phloem.
-build up of sucrose and other carbohvdrates
draws water into the companion cells through
osmosis.
-rigid cell walls combined with the
incompressibility of water result in a build-up of
pressure.
-water will flow from this area of high pressure to
an area of low pressure.
-at the sink end, sucrose is withdrawn from the
phloem and either utilized as an energy source
for such processes as growth or converted to
starch.
-the loss of solute causes a reduction in osmotic
pressure and the water that carried the solute to
the sink is then drawn back in to the transpiration
stream in the xylem.
9.2
is the
most prevalent
solute in phloem
sap.
Sucrose is the most prevalent solute in phloem
sap.
9.2 Outline why
sucrose is used for
phloem transport,
as opposed to
glucose.
Sucrose is not as readily available for plant tissues
to metabolize directly in respiration and therefore
makes a good transport form of carbohydrate as
it will not be metabolized during transport.
9.2
Phloem becomes
to xylem
due to the active
transport of sucrose
into the phloem.
Phloem becomes hypertonic to xylem due to the
active transport of sucrose into the phloem.
Water moves into the phloem by osmosis.
Water moves into
the phloem by
Phloem becomes hypertonic to xylem due to the
active transport of sucrose into the phloem.
Water moves into the phloem by osmosis.
9.2 State the
functions of
phloem.
-loading of carbohydrates at a source
-transport of carbohydrates through the plant
-unloading of carbohydrates at a sink.
9.2 Outline the
structure and
function of
companion cells.
-sieve tube cell and its companion cell share the
same parent cell, so they are closely associated
-companion cells perform many of the genetic
and metabolic functions of the sieve tube cell and
maintain the viability of the sieve tube cell.
-abundant mitochondria in the companion cell
support active transport of sucrose.
-infolding plasma membrane increases the
phloem loading capacity using the apoplastic
route.
-accumulation of sucrose in the sieve tube
element-companion cell pair requires the presence of active transport proteins or enzyme
activity in the companion cells to produce
oligosaccharides.
92 State two ways
xylem cells can be
identified in cross
sections of stem
and root.
-xylem cells are generally larger than phloem
cells. (within one vascular bundle)
-phloem cells tend to be closer to the outside of
the plant in stems and roots.
9.3 Define
indeterminate
growth and
totipotent.
indeterminate growth: plant growth in which the
main stem continues to elongate indefinitely
without being limited
totipotent: a cell that has the capacity to form an
entire organism.
9.3 Most plants
have
growth and have
cells.
Most plants have indeterminate growth and have
totipotent cells.
9.3 Define meristem.
A group of undifferentiated cells which have the
ability to continually divide by mitosis.
9.3 Compare apical
and lateral
meristems.
Apical meristems:
-found at the terminal bud of the stems
-shoot in flowering plants
-cause the plant to increase in length, primary
growth.
-occur at the apices (tips) of the root.
Lateral meristems:
-located in the cambium
-cause the plant to increase in girth, secondary
growth
-results in extra (secondary) xylem growth in a
ring inside the cambium
9.3 Outline role of
mitosis in the
growth of stem and
leaves while
maintaining a
meristem.
-cells in meristems are small and go through the
cell cycle repeatedly to produce more cells, by
mitosis and cytokinesis.
-new cells absorb nutrients and water and so
increase in volume and mass.
-the root apical meristem is responsible for the
growth of the root.
-the shoot apical meristem throws off the cells
that are needed for the growth of the stem and
also produces the groups of cells that grow and develop into leaves and flowers.
-with each division, one cell remains in the
meristem while the other increases in size and
differentiates as it is pushed away from the
meristem region.
9.3 State the
generic function of
plant hormones.
A hormone is a chemical message that is
produced and released in one part of an
organism to have an effect in another part of the
organism.
9.3 Outline the role
of auxin in apical
dominance.
Auxin has a role in stimulating growth at the shoot
apex, inhibiting lateral shoot growth which is
apical dominance
-production of auxins additionally prevents
growth in lateral (axillary) buds, a condition known as apical dominance
-ensures that a plant will use its energy to grow
up towards the light in order to outcompete other
plants
-as the distance between the terminal bud and
axillary bud increases, the inhibition of the axillary
bud by auxin diminishes
Different species of plants will show different
levels of apical dominance
9.3 State two
external factors that
control the growth
of roots and stems.
Light and gravity
9.3 Define tropism,
phototropism and
gravitropism.
Tropism: a response that is determined by the
direction of the stimulus
Phototropism: the growth of shoots towards light
(positive tropism)
Gravitropism: the growth of shoots away from
gravity (negative tropism)
9.3 Explain how
auxin
concentrations
allow for
gravitropism in the
root.
-the upward growth of shoots and the downward
growth of roots occurs in response to gravity.
-if a root is placed on its side, gravity causes
cellular organelles called statoliths to accumulate
on the lower side of cells.
-leads to the distribution of PIN3 transporter
proteins that direct auxin transport to the bottom
of the cells.
-high concentrations of auxin inhibit root cell
elongation so the top cells elongate at a higher
rate than the bottom cells causing the root to
bend downward.
9.3 Auxin influences
cell growth rates by
Auxin influences cell growth rates by changing
gene expression.
9.3 Define
micropropagation.
Micropropagation is the propagation of plants
from a very small sample of tissue, generating
clones.
9.3 Outline how
changing auxin and
cytokinin ratios can
lead to
development of
roots or shoots
from the same
explant tissue.
Micropropagation is carried out in sterile
conditions.
(1) a small sample tissue is excised from the plant
tissue and is sterilised.
(2) it is placed onto nutrient agar containing equal
concentrations of auxin and cytokinin.
-promotes cell division and a mass of
undifferentiated cells (callus) is formed
(3) the callus can be split and each part allowed
to grow.
(4) the callus is then transferred onto nutrient agar
containing more cytokinin than auxin to promote
shoot development.
(5) the shoots are then transferred onto nutrient
agar containing more auxin than cytokinin to
promote root development.
(6) plantlets formed are transferred into soil.
9.3 Outline three
roles of
micropropagation
of plant species
1) new plants can be produced in large numbers
from small amounts of starting material.
(2) virus free plants can be produced. The high
auxin concentration, high rate of cell division and
lack of vascular tissue all have a negative affect
on virus presence.
(3) orchids and other rare species can be
produced in large numbers. Many exotic plants
(with a high market value) are available for the
horticultural industry.
93 Outline role of
microarrays in
understanding role
of plant hormones.
Microarrays allow researchers to detect gene
expression. If a gene is being expressed, then
when the tissue is tested on the microarray, it will
cause fluorescence
9.4 Compare the
vegetative and
reproductive
phases of the
angiospermatophyt
a life cycle.
Vegetative state:
-when a seed germinates, a young plant is formed
that grows roots, stems and leave
-can last for weeks, months or vears, until a
trigger causes the plant to change into the
reproductive phase and produce flowers.
the change from the vegetative to the
reproductive phase happens when meristems in
the shoot start to produce parts of flowers
instead of leaves.
9 4 Flowers are
produced
Flowers are produced from a shoot apical
meristem.
9.4 State two
abiotic factors that
may trigger
flowering.
temperature
day length
9.4 Outline the
process by which
changes in gene
expression trigger
flowering.
-light plays a role in the production of either
inhibitors or activators of genes that control
flowering.
中衣
-in long-day plants, the active form of the
pigment phytochrome leads to the transcription
of a flowering time (FT gene).
-the FT mRNA is then transported in the phloem
to the shoot apical meristem where it is translated
into FT protein.
-the FT protein binds to a transcription factor. This
interaction leads to the activation of many
flowering genes which transform the leaf-
producing apical meristem into a reproductive
meristem.
9.4 State the role of
the pigment
phytochrome.
Leaves use the pigment phytochrome to measure
the length of dark periods.
9.4 Describe role of
phytochrome in
controlling
flowering in long
and short day
plants.
-lonq-day plants: large enough amounts of PFR
remain at the end of short nights to bind to the
receptor, which then promotes transcription of
genes needed for flowering.
-short-day plants: the receptor inhibits the
transcription of the genes needed for flowering
when PFR binds to it. -at the end of long nights,
very little PFR remains, so the inhibition fails and
the plant flowers.
9.4 Define
pollination,
fertilization and
seed dispersal.
Pollination: pollen carried from anther of one
flower to stigma of another
Fertilization: the pollen grain germinates to
produce a pollen tube that carries down the two
male nuclei
Seed dispersal: he scattering of seeds using other
animals or mother nature (wind) to scatter the
seeds
9.4 State the
changes to the
ovule and ovary
that result from
fertilization.
The fertilized ovule develops into a seed and the
ovary develops into a fruit.
9.4 Define
mutualism.
Both species involved in the relationship benefit
from it
9.4 State the
function of the
different parts of
the seed.
Testa - an outer seed coat that protects the
embryonic plant
Micropyle - a small pore in the outer covering of
the seed, that allows for the passage of water
Cotyledon - contains the food stores for the seed
and forms the embryonic leaves
Plumule - the embryonic shoot (also called the
epicotyl)
Radicle - the embryonic root
9.4 Define
germination.
the process by which an organism grows from a
seed or a spore.
9.4 Outline the role
of gibberellin
during germination.
-a metabolic process that occurs at the start of
germination is synthesis of gibberellin, a plant
hormone.
-several genes have to be expressed to produce
the various enzymes of the metabolic pathway
leading to gibberellin.
-this hormone stimulates mitosis and cell division
in the embryo.
-in starchy seeds it also stimulates the production
of amylase.
-this enzyme is needed to break down starch in
the food reserves into maltose
9.4 Write five
factors that could
affect germination.
Seed too old - not viable anymore.
Soil temperature too high or too low.
Seeds needed light for germination but were
sown below the soil surface.
Soil waterlogged and anaerobic, so seedlings
died of ethanol poisoning.
Soil was too dry and the seeds remained
dehydrated.
9.4 Contrast
traditional
conservation efforts
with newer
strategies of
conservation.
Plants and pollinators have evolved together,
which is coevolution and depend on each other
for survival. The importance of mutualistic
relationships has changed how the protection of
species is viewed. It is not enough to protect only
one species if a species they depend on is not
also protected. The current view is to protect
entire ecosystems.
9.4 Outline the
metabolic
processes that
occur in starchy
seeds during
germination.
Remember, up to TWO “quality of construction”
marks per essay.
a. water absorbed by the seed / seed rehydrated;
b. water activates metabolism;
c. gibberellin synthesized/produced/secreted;
d. gibberellin stimulates the production of
amylase;
e. amylase digests/hydrolyses starch (in
cotvledon) to maltose;
f. maltose converted/hydrolysed to glucose (by
maltase):
g. glucose used in aerobic respiration;
h. glucose used in synthesis/production of
cellulose;
