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
