9 plant biology Flashcards
why is palisade mesophyll located on the upper surface of the leaf
it’s the site of photosynthesis so needs to absorb light
why is spongy mesophyll on the lower surface of the mesophyll
main site of gas exchange so near stomata
why are stomata on the underside of the leaf
prevents obstruction otmaintain an open channel for gas exchange
why is the top of a leaf covered in a thick waxy cuticle
prevents water absorbtion which would affect transpiration
where are vascualr bundles located and why
located centrally to allow for optimal access by all leaf cells
label a plant from the inside out
pith
cortex
epidermis
fucntion of epidermis
waterproof, protect the stem and control gas exchange
what does the cortex and pith do
transport and storae of materials within the stem
what is the cambrium
centrally located, circular layer of undifferentiated cells responsible for lateral growth of the stem
describe the location of the xylem and phloem
xylem located to interior side of bundle and phloem on exterior
where are the vascular bundles located and why
in bundles near the outer edge of the stem to resist compression and bending
functions/adaptations of root hair cells
increase available surface area
central region called the stele and is surrounded by an endodermis with a casparian strip (controls water transport)
what does the pericycle/cambium provide
strength to the root and is also responsible for the development of lateral roots
what converts water in the leaves to vapour
light energy
where does water vapour evaporate from
from leaf to air from stomata
how is a difference in pressure created within the plant
new water absorbed from the soil by the roots, creating a difference in pressure between the leaves (low) and roots (high)
where does water flow in a plant
along pressure gradient to replace the water lost from leaves along xylem. this is called the transpiration stream
as photosynthetic gas exchange requires stomata to be open, transpiration will be affected by the level of…
photosynthesis
how does water get from the roots to the leaves
via the xylem.
function of roots
uptake of water and minerals
cross structure of leaf labelled from outside in
cuticle upper epidermis palisade cells containing chloroplasts spongy mesophyll containing air spaces and the vascular bundles lower epidermis stomata and guard cells
what does the mesophyll layer contain
palisade cells
spongy mesophyll
by what processes does water travel up the xylem
cohesion by hydrogen bonding
how does water travel from the soil into the root cells
osmosis.
due to a high solute concentration inside the cytoplasm, established by active transport of mineral ions
what transmits the pulling force from one water molecule to the next
cohesion of water molecules due to hydrogen bonding
why are cell surfaces moist
water is adhesive to the hydrophilic cellulose in the cell walls
what does water adhering to cellulose allow for
carbon dioxide to dissolve and diffuse into the cytoplasm, and excess oxygen to dissolve out
what is the symplast pathway
osmosis via centre of cells
what is the apoplast pathway
diffuses along cell wall boundaries
what contains the casparian strip
endodermis
apoplast pathway
Involves the cell walls (spaces between cellulose fibres allow water to pass easily)
Water diffuses from the soil to the endodermis where the waterproof Casparian strip prevents further progress through the apoplast pathway
At the Casparian strip water must pass through the selective membrane (by osmosis down a water potential gradient) into the symplast pathway if it is to get into the xylem vessels. This prevents harmful molecules such as toxins or viruses entering the xylem vessels and being transported around the plant because the membrane would not let these molecules past.
symplast pathway
Involves the cytoplasm and vacuoles.
To move into the symplast pathway water must pass through a membrane by osmosis due to a lower water potential in the cytoplasm than the soil water. Water potential in the root hair cells is reduced by the active transport of mineral ions into them from the soil
In the symplast pathway water diffuses along a water potential through pores between cells of the cortex called plasmodesmata
what is the transport system called which moves substances around the plant in special tissue
vascular tissue
what does the xylem transport
water and soluble minerals upwards
what does the phloem transport
transports sugars upwards and downwards
what cells are around the vascular bundle
the endodermis
what is inside the endodermis
a layer of meristem cells called the pericycle
where are the vascular bundles found
near the outer edge of the stem.
xylem inside
phloem outside
what is in between the xylem and phloem vessels
the cambium
LABEL PAGE ON ONENOTE CALLED
- XYLEM AND PHLOEM NTOES
what do the fibres in the xylem do
support the plant and living parenchyma cells
what do xylem walls have
lignin
what does lignin do
make the xylem cell walls waterproog and this causes the cells to die, so their contents and end walls decompose laving a hollow tube of dead cells. the lignin strengthens the tube and prevents the vessel from collapsing
adv of the xylem vessels being narrow
water column doesnt break easily, and capillary action can be effecive
what does lignin being depositied in spiral circles or broken rings allow
the xylem to stretch as the plant grows and enables the stem or branch to bend
what does the phloem consist of
sieve tube elements and companion cells
why are seive tube cells not cells
dont have much cytoplasm and no nucleus
why is sucrose used instead of glucose
glucose would all be respired if that is waht the plant stored
what is the sucrose dissolved in
water to form sap
how does sap flow through the phloem
it contains cross walls at intervals, perforated by many pores to allow the sap to flow. hence the cross walls are called sieve plates and the tubes sieve tubes.
describe companion cells
small cells with large nucleus and dense cytoplasm. large numbers of mitochonfria.
what do companion cells do
carry out the metabolic processes using atp energy, such as loading the sucrose in the tubes
what is translocation
movement of organic compounds from sources to sinks
what is the source
where the organic compounds are synthesised (photosyntehtic tissue like leaves)
what is the sink
where the compounds are delivered to for use or storage (roots, fruit, seeds, tubers)
what are sugars principally transported as
sucrose (disaccharide) as it is soluble but metabolically inert
why do sieve elements have thick and rigid cell walls
to withstand the hydrostatic pressures which facilitate flow
how do companion cells increase SA:vol
infolding plasma membrane for more material exchange
where are transport proteins in the companion cells
in the plasma membrane
why can sieve elements not sustain independendent metabolic activiy without the support of a companion cell
sieve element cells have no nuclei and fewer organelles to maximise flow rate
what are plasmodesmata
narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them
what do plasmodesmata mediate
symplastic exchange of metabolites
which of the plant vessels ahve larger cavities
xylem
monocotyledon
flowering plant with an embryo that bears a single cotyledon (seed leaf)
dicotyledon
flowering plant with an embryo that bears two cotyledons (seed leaves)
differences in monocotyledons and dicotyledons in xylem and phloem arrangement in roots
in monocotyledons, the stele is large and vessels form a large circle around the central pith
xylem more internal, phloem more external.
in dicotyledons, the stele is very small and the xylem is located centrally with the phloem surrounding it. xylems may form x like shape, while phloem situated in surrounding gaps
where are monocotyledons in stems
vascular bundles found in a scattered arrangement throughout the stem
where are dicotyledons in stems
arranged in a circle around the centre of the stem (pith). phloem and xylem separated by the cambium
how are organic compounds actively loaded into phloem sieve tubes by companion cells
materials can pass into the sieve tube via interconnecting plasmodesmata (symplastic loading)
alternatively materials can be pumped across the intervening cell wall by membrane proteins (apoplastic loading)
describe the active transport process of glucose entering phloem sieve tubes
Hydrogen ions (H+) are actively transported out of phloem cells by proton pumps (involves the hydrolysis of ATP)
The concentration of hydrogen ions consequently builds up outside of the cell, creating a proton gradient
Hydrogen ions passively diffuse back into the phloem cell via a co-transport protein, which requires sucrose movement
This results in a build up of sucrose within the phloem sieve tube for subsequent transport from the source
incompressibility of water allows transport along…
hydrostatic pressure gradients
what makes sap solution hypertonic in the source
active transport of solutes into the phloem by companion cells
what does increase in hydrostatic pressure cause
forces the phloem sap to move towards areas of lower pressure (mass flow) so the phloem transports solutes away from the source and towards the sink
at the sink, how does the sap solution become hypotonic
solutes within the phloem unloaded by companion cells and transported into sinks (roots, fruits, seeds etc)
as the sink sap is hypotonic, what happens
the water is drawn out of the phloem and into the xylem by osmosis, so hydrostatic pressure at the sink is always lower than hydrostatic pressure at the source, so phloem sap should move from the source towards the sink
xerophytes
plants that hae adapted to live in conditions where liquid water is difficult to obtain.
adaptations of xerophytes
thick/waxy cuticle on leaf or stem fewer stomata stomata in sunken pits fine hairs along underside of leaf CAM physiology reduced air spaces in leaf mesophyll few/small leaves curled or rolled leaves water storage tissue deep highly branched roots
adaptation of thick waxy cuticle
Reduces non-stomatal transpiration rate because the cuticle is hydrophobic and creates a barrier to prevent water loss.
adaptation of fewer stomata
Reduces transpiration rate by having fewer openings in the leaf.
adaptation of stomata in sunken pits
Reduces transpiration rate by allowing moisture (humidity) to build up near stomata.
adaptation of fine hairs along underside of leaf
Reduces transpiration rate by retaining a layer of moisture near the stomata.
adaptation of CAM physiology
Reduces transpiration rate enormously because stomata close during the day. Stomata open at night to collect and store carbon dioxide, when darkness and cooler temperatures reduce evaporation. During the day, pre-collected carbon dioxide allows photosynthesis to occur without water loss.
adaptation of reeduced air spaces in leaf mesophyll
Reduces transpiration rate due to reduced surface area for evaporation.
adaptation of few small elaves
Reduces transpiration rate because there is reduced surface area for light to strike and water to evaporate.
adaptation of curled or rolled leaves
Reduces transpiration rate because there is reduced surface area for water loss and there can be production of humid areas by the stomata.
adaptation of water storage tissue
Increased water storage when water is available. Succulent plants have tissues in stems or leaves adapted to store large amounts of water; other plants store water in tubers.
adaptation of deep highly branced roots
Increased ability to take up water because deep roots may reach a lower water table beyond the dry soil. Branched roots provide increased surface area for water absorption.
halophytes
plants that have adapted to grow in areas with high salinity, such as along an ocean shoreline or in certain swamps and marshes
adaptations of halophytes
salt storage in vacuoles high conc of organic solutes salt storage glands in leaf leaf abscission for some leaves selectively permeable membrane in root cells xerophytic adaptations
adaptation of salt storage in vacuoles
Compartmentalises salt in vacuoles, thus protecting cellular organelles and enzymes from damage by high salt concentration.
adaptation of high conc of organic solutes
Increases osmolarity by having a high concentration of sugars and other solutes, thus water can still enter by osmosis.
adaptation of salt storage glands in leaf
Accumulates salt in a limited area by filling the salt glands until they release salt crystals onto the leaf surface where they will fall off or be dissolved in rain.
adaptation of leaf abscission for some leaves
Removes salt by breaking off leaves with toxic levels of salt and letting them fall from the plant.
adaptation of selectively permeable membrane in root cells
Excludes salt by having no ion channels to allow passage of Na + and Cl - , and/or has active transport pumps to remove the ions.
adaptation of halophytes by having xerophytic adaptations
Conserves water by having few stomata, water storage tissue, thick cuticle and other adaptations listed in Table 1 .
internal factors affecting rate of transpiration
Root to shoot ratio
Surface area of leaves
Number of stomata per unit leaf area
Leaf structure, for example, the presence of hair or thick waxy cuticle.
external factors affecting rate of transpiration
Light Wind Temperature Humidity Water availability.
how does light effect rate of transpiration
Stomata are closed in the dark, but as light intensity increases stomata open and allow water vapour to escape from the air spaces of the leaves. Therefore, bright sunlight increases the rate of transpiration. Photons also provide energy for evaporation .
how does wind effect rate of transpiration
In low wind conditions, the air underneath leaf becomes increasingly humid. This reduces the water vapour concentration gradient from the leaf’s air spaces to the outside air, and so reduces the rate of transpiration. As wind speed increases, the humid air is blown away more quickly and is replaced by drier air, which increases the rate of transpiration due to the increased concentration gradient for water vapour. However, if the wind speed reaches a critical level, the stomata may close to reduce the rate of transpiration.
how does temperature effect rate of transpiration
Higher temperatures provide more energy for evaporation of water from the cell walls and decrease the humidity of the external atmosphere. However, if the temperature gets too high for enzymes to function efficiently, the stomata may close and the transpiration rate may fall.
how does humidity effect rate of transpiration
Humidity refers to the percentage of water vapour present in the atmosphere. When the air surrounding a leaf is dry (low humidity), the concentration gradient for diffusion of water vapour from the air spaces within the leaf to the outside is steep and transpiration occurs quickly.
where is growth in a plant concentrated
in the meristem at the tip of the roots and shoots
what happens to the cells at the very tip (apex) as new cells are fomed
remain meristematic.
what are the areas called when the cells at the apex remain meristematic as the plant grows
apical meristems
what is indeterminate growth
rapid growth when young and slower growth when adult
what are the stem cells in the meristem
undifferented cells
what does the root cap do
protect the meristem and shed cells
half of the cells produced in the meristem remain..
undifferentiated while the other half specialises and contributes to growth and development
what do the cells produced by the shoot apical meristem develeop
leaves buds and any other above ground structures
what does the procambium give rise to
the xylem and phoem
what does the protoderm become
the epidermis
what does the ground meristem become
the cortex and mesophyll
what does the leaf primordia develop into
fully functional and differentiated leaves
what does the apical meristem create
dormant meristems in the auxillary buds, where the leaf joins the stem, that have the potential to grow into new shoots or branches
describe the route of auxin
synthesised in the apical meristem and travels down the stem.
auxin causes..
cell elongation and inhibition
what does auxin inhibit
growth of auxiliary buds, causing the plant to grow vertically upwards to trap more light for photosynthesis. this is known as apical dominance
what happens when the shoot apex has grown far enough above an auxilary bud
the auxin concentration becomes too low to inhibit growth and the buds begin to develop
tropism def
directional growth in response to an external stimulus, such as light, gravity, touch, water, or chemicals. Plant shoots respond to their environment through tropisms.
phototropism
resposne to light
geotropism
reponse to gravvity
shoot show
positive phototropism and negative gravitropism.
roots show
positive gravitropism and negative phototropism
thigmotropism
response to touch
chemotropism
response to chemicals
hydrotropism
response to water
when is auxin produced
when light is overhead
what happens when sunlight is significantly more on one side
the auxin transporters redistribute auxin so it accumulates on the shaded side. the cells then grow faster, causing the shoot to bend towards the ligth
what does auxin do in roots
inhibit growth. auxin is affected by growth in roots.
how can auxin travel around a plant
bulk flow of the phloem and also actively moved fom cell to cell through several methods
when phototropins detect equally bright light on all sides…
auxin moves symmetrically downard, being pumped into and out of successive layers of cells through specialised protein pumps.
where do plant cells have auxin influx carriers
in their apical membranes and auxin efflux carriers in their bottom (basal) membranes
what happens when phototropins detect diference in brightness on different sides of the shoot
some auxin efflux carriers increase on the internal lateral side membrane. this causes transport of auxin to the shaded side of the plant and establishes a conc grad. the shaded side of the shoot experiences greater cell elongation, bending the stem toward the light
how does auxin stimulate cell elongation in the sem
Auxin stimulates proton pumps that use ATP to move protons (hydrogen ions, H + ) out of the cytoplasm and into the cell wall.
A higher H+ concentration in the cell wall means the cell wall becomes more acidic (a decreased pH).
The acidic pH breaks bonds between cellulose fibres in the cell wall directly by disrupting hydrogen bonding and indirectly by activating pH-dependent expansin proteins that sever cellulose connections.
The reduced number of bonds between cellulose microfibrils makes the cell wall more flexible.
Cellulose fibres can slide apart as they are pushed by turgor pressure inside the cell, thus the cell elongates as the cell wall becomes softer and more flexible.
meristematic plant cells are…
totipotent (can differentiate in to any plant tissue)
what is micropropogation
A small tissue sample is taken, usually from the shoot apical meristem, and sterilised. It is grown in a sterile medium with concentrations of auxin that promote cell growth but not differentiation. This produces a large mass of undifferentiated cells called a callus. The callus can then be broken up to create many tiny cell samples that are grown in a different medium, this one with concentrations of hormones that trigger cell differentiation and plant development.
micropropogation def
a method used to mass produce clones of a parent plant. It involves the use of tissue culture techniques for meristematic tissue or somatic cells on nutrient media under controlled sterile conditions.
benefits of micropropgation
rapid increase in numbers of plants
production of virus free indiviuals of existing varieteis
production of orchids and other rare species
what controls the opening and closing of stomata
guard cells
waht do guard cells contain
chloroplasts
how dose the spongy mesophyll enable photosynthesis
large surfacce area and moist surface necessary for gases to be exchanged
what is a competitive inhibitor
competes with the susbtrate for the same active site
what are non competitive inhibitors
competes with the substrrate but binds at a site away from the active site, altering the shape of the enyzme
why is it important to lower the conc of oxygen gas during photosyntheiss
it is a competitive inhibitor of rubisco
what dose rubisco do
involved in the fixation of CO2 in chloroplasts
where does transpiration occur
through open stomata
waht effect does transpiration have on the plant
cooling effect
gas exchange
exerts a pull to move water from the roots into the leaves
what is a CAM physiology
Reduces transpiration rate enormously because stomata close during the day. Stomata open at night to collect and store carbon dioxide, when darkness and cooler temperatures reduce evaporation. During the day, pre-collected carbon dioxide allows photosynthesis to occur without water loss.
what are the xylem walls strengthened with
lignin (binds with cellulose)
benefits of lignin
can support plants many metres tall. Lignin also allows the xylem vessels to withstand the forces involved in transpiration without collapsing. Lignin can be deposited throughout the cell walls or as rings or spirals inside the xylem vessels.
how do the celluslose in mesophyll walls enable transpiration
its hydrophilic and so water adheres to it, creating a film of water on the cells. When water vapour diffuses out of the stomata, the internal air spaces of the leaf become less humid. Water then evaporates from the moist mesophyll cell walls into the air spaces. cohesion pulls up the rest of the water
describe water’s cohesion
the attraction between the slightly negative oxygen atom in one water molecule and the slightly positive hydrogen atoms in a different water molecule creates hydrogen bonds between water molecules.
cohesion is
water molecules form weak hydrogen bonds with each other due to their polarity. This allows transpiration pull to extend, unbroken, through long columns of water in xylem vessels.
adhesion is
the polarity of water also interacts with the hydrophilic cellulose in the cell walls of the leaf. This helps create the pull that draws water out of the xylem and into the leaf cells.
the plasma membrane of the root hairs has many…
protein pumps that actively transport mineral ions from the surrounding water into the cytoplasm of the cell against the concentration gradient
Due to the high demand for ATP, root hairs have
a high rate of cellular respiration, many mitochondria, and a high demand for oxygen gas. The oxygen is dissolved from air pockets in the soil into the surrounding water and from there diffuses into the root cells.
how does water move into the plant root cells
via osmosis due to the high conc of mineral ions in the cytoplasm
internal factors affecting rate of transpiration
Root to shoot ratio
Surface area of leaves
Number of stomata per unit leaf area
Leaf structure, for example, the presence of hair or thick waxy cuticle.
external factors affecting rate of transpiration
Light
Wind
Temperature
Humidity
Water availability.
~~~
light effect on transpiration
As light intensity increases , the rate of transpiration increases.
. Stomata are closed in the dark, but as light intensity increases stomata open and allow water vapour to escape from the air spaces of the leaves. Therefore, bright sunlight increases the rate of transpiration. Photons also provide energy for evaporation .
wind effect on transpiration
As wind velocity increases , the rate of transpiration increases
. In low wind conditions, the air underneath leaf becomes increasingly humid. This reduces the water vapour concentration gradient from the leaf’s air spaces to the outside air, and so reduces the rate of transpiration. As wind speed increases, the humid air is blown away more quickly and is replaced by drier air, which increases the rate of transpiration due to the increased concentration gradient for water vapour. However, if the wind speed reaches a critical level, the stomata may close to reduce the rate of transpiration.
temperature effect on transpiration
As temperature increases, the rate of transpiration increases .
Higher temperatures provide more energy for evaporation of water from the cell walls and decrease the humidity of the external atmosphere. However, if the temperature gets too high for enzymes to function efficiently, the stomata may close and the transpiration rate may fall.
himidiity effect on transpiration
As humidity increases , the rate of transpiration decreases .
Humidity refers to the percentage of water vapour present in the atmosphere. When the air surrounding a leaf is dry (low humidity), the concentration gradient for diffusion of water vapour from the air spaces within the leaf to the outside is steep and transpiration occurs quickly.
which plants have a xylem and phloem
vascular plants
translocation in the phloem is a …
active process requiring an input of ATP.
how are sieve elements and companion cells connected by
the plasmodesmata
what does the phloem consist fo
columns of living cells called sieve tubes. each cell in a sieve tube is called a sieve element with a companion cell
what are the walls connecting sieve elements
they become perforated during development to form sieve plates
what do sieve plates contain
sieve pores
cell walls of the phloem
cellulose
why does the phloem have Reduced organelles in sieve elements
Absence of cell structures (including nucleus, cytoskeleton, golgi, ribosomes and vacuole) frees the lumen to conduct a large volume of sap
why does the phloem have companion cells
Metabolic support cells (containing all the standard organelles) provide biomolecules (e.g. enzymes) necessary to maintain life functions in the sieve elements
why does the phloem have a plasmodesmata
Openings between the sieve elements and companion cells allow communication and support from companion cells
why does the phloem have a sieve plate
Pores through the horizontal cells that join sieve elements allow sap to flow freely
why does the phloem have a cell membrane
Presence of a fully functional cell membrane in sieve elements that contains specialised protein pumps provides the structures needed to control the composition of sap
fucntion of plasmodesmata
Passageways for communication between sieve tubes and companion cells
sources:
produce more sugar than needed
sinks:
need more sugars than produced
sources def
are photosynthesising tissues and storage organs that are exporting sugars to other parts of the plant.
sinks def
organs that cannot produce (sufficient) sugars and need them for respiration or storage.
describe how something can be a sink at some stages and a source at others
while an onion is developing and growing, it is a sink beacuse it is recieving sugars for storage. later, it will release its stored carbohydrates to noursih embryonic leaves, acting as a source.
translocation
active loading of sucrose into the phloem tubes increases the solute conc in the sieve tubes.
this causes wate to move from the xylem to the sieve tubes by osmosis.
this leads to a high hydrostatic pressure at the source, so mass flow occurs, where water and solute move away from the source and towards the sink.
at the sink, companion cells unload the sugars from the sive tubes, actively or passively.
this allows water to return to xylem.
lower hydrostatic pressure allows sap to flow to the sinks, down hydrostatic pressure gradietns.
what is phloem loading
The process by which soluble carbohydrates (sugars) enter the phloem
what is the primary sugar transported by the phloem
sucrose
what causes sucrose to enter a companionc ell
active transport
movement processes in xylem vs phloem
phloem: translocation
xylem: transpiration
why does translocation occur in the phloem
Hydrostatic pressure gradients in phloem
ATP for loading sugar into phloem at source, water follows by osmosis
why does transpiration occur in the xylem
Evaporation and cohesion-tension creating transpiration pull
ATP for loading ions into roots, water follows by osmosis
materials transported in the phloem
Sucrose and other organics (other sugars, hormones, amino acids, proteins)
materials transported in the xylem
Water and dissolved minerals
direction of movement in the phloem
source to sink (bidirectional)
direction of movement in the xylem
roots to shoots (leaves)
up only
cellular structure of the phloem
Columns of living cells called sieve tube elements
cellular structure of the xylem
Columns of dead cells called xylem vessels
horizontal end walls of the phloem
Perforated walls called sieve plates allow the continuous flow of sap
horizontal end walls of the xylem
Continuous hollow tube with removed end walls allows an unbroken column of water
special features of the phloem
Connected by plasmodesmata to companion cells that support metabolic functions
special features of the xylem
Thickened cell walls consisting of lignin making strong, woody tissue
phloem is always located close to the ?? of the plant than xylem
surface
continuous growth of plants is due to
Undifferentiated cells in the meristems of plants
how is auxin transported from cell to cell
auxin influx and efflux proteins.
In micropropagation, why do cells from the callus need to be transferred to a second, different growth medium
To provide different concentrations of chemicals to trigger cell differentiation.
radicle
embryonic root
plumule
embryonic shoot
hypocotyl
a shoot above the root and below the cotelydons
cotyledons
modified leaves that store food for the embryo
testa
seed coat that protects the embryo and food stores
hilum
a scar where the seed was attatched to the ovary
micropyle
a small pore above the hilum where the pollen tube entered to allow fertilisation
sepal
a leaf like structure that encloses the bud of the flower
stigma
sticky portion at the top of the style where pollen grains land
style
the narrow elongated part between the ovary and the stigma
ovary
the organ that protects the ovules of a flower, and develops into a fruit
ovule
a structure that develops in the ovary and contains the female gamete. develops into seeds
stamen
the male reproductive organ of a flower, consisting of an anther and a filament
anther
structure which produces pollen grains
filament
a long thin structure that supports an anther
pollen
the fine dust like granules that contain the male gametes of seed plants
petal
brightly coloured structure that attracts the insects to a flower
carpel
the female reproductive organ of a flower, consisting of the stigma, style and ovary.
what is the micropyle
a small gap/hole in the inwards bending side of the seed
pollination
delivery of pollen to the stigma of a flower
most common pollinators
insects
fertilisation
fusion of th sperm and the egg to create a diploid zygote
where does fertilisation occur
in the ovule
what happens during fertilisation
pollen grain grows a tube through the style to allow the sperm to traced from the stigma to the ovule. flowers must be pollinated before the eggs can be fertilised.
three requirements of germination
water
oxygen
temperature
how is water needed during germination
For metabolic reactions to occur, the seed must first rehydrate by taking in water through imbibition (Imbibition is a special type of diffusion that takes place when water is absorbed by solids-colloids causing an increase in volume. Examples include the absorption of water by seeds and dry wood). This is a passive process, because the solutes in the seed are highly concentrated.
how is oxygen needed during germination
The embryonic plant will need a great deal of oxygen because it will have a high rate of growth and metabolism. This means a high rate of oxygen-consuming cellular respiration. The plant does not have mature leaves during germination and thus does not perform photosynthesis or produce oxygen.
how is temperature needed during germination
Different seeds have different optimal growth temperatures, but they all require temperatures that allow enzymes to function well. Temperatures that are too high can denature enzymes, while cold temperatures can slow enzyme activity substantially.
