Bio9

Question 1

91 What is the vein
composed of, and
describe their
functions.

Answer 1

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.

Question 2

9.1 Describe and
explain the process
of transport of
water (capillary
action) in plants.

Answer 2

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.

Question 3

9.1 What factors
allow the xylem
vessels to transport
under tension.

Answer 3

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.

Question 4

91 How do roots
absorb water and
mineral ions present
from the soil?
Explain the
processes

Answer 4

1. 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.
2. 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.
3. 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

Question 5

9.1 Skill: Drawing the
structure of primary
xylem vessels in
sections of stems
based on
microscope images.

Answer 5

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

Question 6

9.1 Application:
Describe simple
models of water
transport, inclusive
of evaporation,
adhesion and
cohesion.

Answer 6

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

Question 7

9.1 Skill: Design of
an experiment to
test hypotheses
about the effect of
temperature or
humidity on
transpiration rates.

Answer 7

-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

Question 8

9.1 What causes the
hydrogen to bond,
and what makes it
strong?

Answer 8

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.

Question 9

9.1 What is
produced to force
closure of the
stomata?

Answer 9

The hormone abscisic acid

Question 10

9.1 Why don’t xylem
cells contain any
cytoplasm?

Answer 10

It is a dead cell. It grows into size, and remains
dead to provide larger lumen making water
transport more efficient.

Question 11

9.2 Application:
Structure-function
relationships of
phloem sieve tubes.
What are phloem
sieve tubes
primarily composed
of and what are
their individual
functions?

Answer 11

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

Question 12

9.2 Describe the
process of
translocation in
phloem.

Answer 12

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

Question 13

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.

Answer 13

-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.

Question 14

9.3 What are the
undifferentiated
cells in plants and in
what ways does it
allow growth?

Answer 14

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.

Question 15

9.3 Describe the
process of mitosis in
meristematic cells
and its function.

Answer 15

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.

Question 16

9.3 What is the
name of the plant
hormone, and what
are its functions in
plants?

Answer 16

Auxin controls growth and cell division within the
shoot apex
Auxin is produced and plant shoots grow and
respond to the environment by tropisms

Question 17

9.3 How do plants
grow depending on
the environmental
conditions?
Describe the
process

Answer 17

-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.

Question 18

9.3 How can auxin
influence cell
growth rates?

Answer 18

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.

Question 19

9.4 Describe how
flowers are grown
out of plants in
order for plants to
reproduce.

Answer 19

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.

Question 20

9.4 Describe how
plants response to
the length of light
and dark periods.

Answer 20

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.

Question 21

9.4 Application:
What methods are
used to induce
short-day plants to
flower out of
season? Provide an
example.

Answer 21

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.

Question 22

9.4 What
relationship does
plant have with the
pollinators, and
what are the
benefits?

Answer 22

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.

Question 23

9.4 What are the
stages to plant
reproduction?

Answer 23

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

Question 24

9.4 Skill: Drawing of
half-views of
animal-pollinated
flowers. List out the
structures in animal
pollinated flowers
and briefly
mentions its
functions.

Answer 24

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

Question 25

9.4 Skill: Drawing internal structure of seeds. List out the structures of the seed and its functions.

Answer 25

-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

Question 26

9.4 Skill: Design of experiments to test hypotheses about factors affecting germination.

Answer 26

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

Question 27

9.1 Draw a labelled diagram showing the tissues present in a dicot leaf.

Answer 27

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)

Question 28

9.1 Explain the functions of the different tissues of the leaf.

Answer 28

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

Question 29

9.1 Outline the adaptations of plant roots for absorption of mineral ions from the soil.

Answer 29

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;

Question 30

9.1 Describe the process of mineral ion uptake into roots.

Answer 30

• 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

Question 31

9.4 Explain the conditions needed for seed germination.

Answer 31

• 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

Question 32

9.1 Define transpiration.

Answer 32

Transpiration is the loss of water vapour from the stems and leaves of plants.

Question 33

9.1 Explain gas exchange that occurs through leaf stomata.

Answer 33

-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

Question 34

9.1 Explain structures and mechanisms involved in the flow of water from roots to leaves.

Answer 34

• 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;

Question 35

9.1 Explain the regulation of water loss in plants. *this question is out of our syllabus

Answer 35

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

Question 36

91 Describe structure of xvlem.

Answer 36

-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.

Question 37

9.1 Explain how xylem is able to maintain rigidity even under low pressure or mechanical disturbance.

Answer 37

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

Question 38

9.1 Outline polarity of water molecule.

Answer 38

-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.

Question 39

9.1 Define cohesion.

Answer 39

Cohesion is the force of attraction between two particles of the same substance (e.g. between two water molecules)

Question 40

9.1 Explain the decrease in pressure and transpiration-pull that results from evaporation of water from the leaf.

Answer 40

• 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.

Question 41

9.1 Outline why roots are hypertonic relative to the soil.

Answer 41

-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

Question 42

91 Outline the role of active transport in maintaining root tonicity.

Answer 42

-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.

Question 43

9.1 Describe how water enters roots from the soil and transported throughout the plant.

Answer 43

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;

Question 44

91 Compare the symplastic and apoplastic pathways of water transport through the root.

Answer 44

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.

Question 45

9.1 Define xerophyte and halophytic.

Answer 45

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

Question 46

9.1 Application: Outline strategies used by xerophytes and halophytes to reduce water loss.

Answer 46

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)

Question 47

91 Describe the use of a potometer to measure transpiration rates.

Answer 47

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

Question 48

9.1 Explain the factors that can affect transpiration in a typical terrestrial plant.

Answer 48

(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

Question 49

9.1 State a similarity and a difference between transpiration models and transpiration in plant tissues.

Answer 49

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

Question 50

9.2 Define translocation, phloem sap, source and sink.

Answer 50

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

Question 51

9.2 List example source and sink tissues.

Answer 51

Sources: -mature leaves Sinks: -roots -tubers -developing fruits -immature leaves

Question 52

9.2 Explain why phloem transport can be bidirectional.

Answer 52

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.

Question 53

9.2 Outline why pressure in the phloem increases due to the movement of water into the phloem.

Answer 53

-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.

Question 54

9.2 is the most prevalent solute in phloem sap.

Answer 54

Sucrose is the most prevalent solute in phloem sap.

Question 55

9.2 Outline why sucrose is used for phloem transport, as opposed to glucose.

Answer 55

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.

Question 56

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

Answer 56

Phloem becomes hypertonic to xylem due to the active transport of sucrose into the phloem. Water moves into the phloem by osmosis.

Question 57

9.2 State the functions of phloem.

Answer 57

-loading of carbohydrates at a source -transport of carbohydrates through the plant -unloading of carbohydrates at a sink.

Question 58

9.2 Outline the structure and function of companion cells.

Answer 58

-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.

Question 59

92 State two ways xylem cells can be identified in cross sections of stem and root.

Answer 59

-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.

Question 60

9.3 Define indeterminate growth and totipotent.

Answer 60

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.

Question 61

9.3 Most plants have growth and have cells.

Answer 61

Most plants have indeterminate growth and have totipotent cells.

Question 62

9.3 Define meristem.

Answer 62

A group of undifferentiated cells which have the ability to continually divide by mitosis.

Question 63

9.3 Compare apical and lateral meristems.

Answer 63

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

Question 64

9.3 Outline role of mitosis in the growth of stem and leaves while maintaining a meristem.

Answer 64

-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.

Question 65

9.3 State the generic function of plant hormones.

Answer 65

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.

Question 66

9.3 Outline the role of auxin in apical dominance.

Answer 66

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

Question 67

9.3 State two external factors that control the growth of roots and stems.

Answer 67

Light and gravity

Question 68

9.3 Define tropism, phototropism and gravitropism.

Answer 68

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)

Question 69

9.3 Explain how auxin concentrations allow for gravitropism in the root.

Answer 69

-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.

Question 70

9.3 Auxin influences cell growth rates by

Answer 70

Auxin influences cell growth rates by changing gene expression.

Question 71

9.3 Define micropropagation.

Answer 71

Micropropagation is the propagation of plants from a very small sample of tissue, generating clones.

Question 72

9.3 Outline how changing auxin and cytokinin ratios can lead to development of roots or shoots from the same explant tissue.

Answer 72

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.

Question 73

9.3 Outline three roles of micropropagation of plant species

Answer 73

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.

Question 74

93 Outline role of microarrays in understanding role of plant hormones.

Answer 74

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

Question 75

9.4 Compare the vegetative and reproductive phases of the angiospermatophyt a life cycle.

Answer 75

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.

Question 76

9 4 Flowers are produced

Answer 76

Flowers are produced from a shoot apical meristem.

Question 77

9.4 State two abiotic factors that may trigger flowering.

Answer 77

temperature day length

Question 78

9.4 Outline the process by which changes in gene expression trigger flowering.

Answer 78

-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.

Question 79

9.4 State the role of the pigment phytochrome.

Answer 79

Leaves use the pigment phytochrome to measure the length of dark periods.

Question 80

9.4 Describe role of phytochrome in controlling flowering in long and short day plants.

Answer 80

-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.

Question 81

9.4 Define pollination, fertilization and seed dispersal.

Answer 81

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

Question 82

9.4 State the changes to the ovule and ovary that result from fertilization.

Answer 82

The fertilized ovule develops into a seed and the ovary develops into a fruit.

Question 83

9.4 Define mutualism.

Answer 83

Both species involved in the relationship benefit from it

Question 84

9.4 State the function of the different parts of the seed.

Answer 84

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

Question 85

9.4 Define germination.

Answer 85

the process by which an organism grows from a seed or a spore.

Question 86

9.4 Outline the role of gibberellin during germination.

Answer 86

-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

Question 87

9.4 Write five factors that could affect germination.

Answer 87

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.

Question 88

9.4 Contrast traditional conservation efforts with newer strategies of conservation.

Answer 88

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.

Question 89

9.4 Outline the metabolic processes that occur in starchy seeds during germination.

Answer 89

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;